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MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS-1963-A I 1I1 L25 111111.
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RESOLUTION TEST CHART
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I
~~~~~~~~~~~~~~~~~ Technical Bulletin No. 698
~
December 1939
UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C. RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION 1 By D,WID I.
BLUMENSTOCK, j1Ln'ior soil cOllscrvaf·ionisl, Climatic and Physl:ographic
DivisIon, Ojfice of Research, Soil Conservation Service
2
CONTENTS
Page
Significance
the precipitation factor In soU
erosion _____of. ___
The problem of analyzing pN~lpitation data.
Contrasts between local and geneml
storms_. ____ .• ___ ....... _... ______ .. __ . 4
9
Interpreting individual station records ..•.
Areas and stations selected for study... ___ _
10
Types of analyses undertaken. ____ .... _._. __
11
Data utUized and methods ofcompUation ___ _
11
Analysis of monthly and annual minfal!
amounts ..____ . ______ . _. _______ •___ • _. ___ ..
12
Ralnfall·intenslty factor. _________________ • ___
15
H ' _ • • ___
-._
• • _______ •
____ _
Rainfall duration. ____________________________
Length of periods without preclpltatlon_____ ..
Diurnal variations In mlnCall amounts __ .... _..
Regional mlnCall chamcterlstlcs and their
relation to soil erosion_._. _ ....... _._. __
Virginla-\Vest Vlrginisaren •• _... _.... _..
South-central prairie region. __ .. ,_ .... _•••
Southern Gr"st. Plains region ..... _.......
Extension oC the present mode oC inquiry to
include other areas. ____ .... ____ .... ___ .. _..
Lltemture clted_ .. ___ • ________________________
Appendix._.._________________________________
Page
18
!!O
25
26 26
26
27
2S
29
29
SIGNIFICANCE OF THE PRECIPITATION FACTOR IN SOIL EROSION
Of the erosion mechauisms, only wiud and gravity movements can
occur without the presence of water. Water ill either the liquid or
solid stn,te is involved ill such weathering proce~jses as frost heaying,
exfoliation through hydration and dehycirat,ion, and numerous chem­
ical reactions that require a solvent in order t,o take place, Stream
erosion, gullying, sheet wash, trenching, slumping, and solifluction
are a few of the numerous erosional processes that depend on water
for their operation.
It is not surprising, therefore, that of all the climatic factors that
basically influence erosion, precipitation is the most important.
Under natural conditions the precipitation, through its influence on
vegetation and soils, largely determines the effectiveness of natural
checks to erosion; and, inasmuch as precipitation is the sole source
of the water that participates in erosion, it also determines the force
with which various erosiollal mechanisms will operate. Thus the
I Submitted Cor publieation January 31, 1939.
I Tbe data on which this study is bllSed were prepared by Richmond T. Zoch. Cormerly assistant soil
conservationist, and L. Vernon Robinson, Cormerly assistant soil conservationist, Boil Conservation Service.
147950°-39-1
1
\
2
TECHNICAL RULLETIN 698, U. S. DEPT. OF AGRICULTURE
partial balance that normnliy exists bet,ween soil-forming and soil­
remo':ing forces is understandable only if the precipitation factor is
given prominent considE'mtion.
The rainfall factor !1SSll111eS even greater importance jn the study
of man-induced erosion. Exposure of the lu,nd through cultivation
find clearing permits those erosional mechanisms associated with pre­
cipitation to opera.te with greu r efficiency, and the erosion forms
produced reflect strikingly the character of the precipitation. Such
specific precipitation characteristics as rn,infali intensity, duration,
storm frequency, nnd storm area must, therefore, be studied in detail
if effective erosion-control mensures are to be adopted.
As Neal (7)3 has shown, minfnll intensity is probably more inl­
pm'tant than uny other factor in its eft'ect on run-oft' and soil erosion.
It seems to hn,e an e,en greater influence on the amount of soil loss
than on tIle amount of nm-off. Where tbe rate of precipitation is
greater than the rate of infiltration, nm-off and soil wustnge increase
with an incrense in precipitation intensity, the relationship heing
exponentiul ('I'). These relatior-lo'hips are expressed in the different
forms of erosion that rains vf various intensities produce. Investi­
gations carried out in South Carolina demonstrate thnt erosion through
gully cutting und sheet wush results from intense precipitation,
whereas g'lilly caving Hnd mass movement in genernl Ilre induced by
rnins of low to moderate iutensities (3).
Storms remaining over an area for some time may cause consider­
able run-oft', with accompnnying soil wastage, alld may result in
serious flooods even though the rainfull intensities mlly not be par­
ticularly high. The flood of March 1936 ill Pelmsylvania was pro­
duced by rainfuli that lusted 13 days; and, in. sp:Le'lf the filet that
24-hour intensities reached 4 inches at some F:.ttions, tlH> prolonged
nature of the storm was the principal factor in creating flood l'Oll­
ditions. 4 Since practicnlly ali such major ca tustl'ophes result from
prolonged ruins, it is essential to consider the duration of a !:'torm as
well as its int.ensity.
The frequency "'itb which rains occur is C1 itical with respect to
both soil-moisture ('onditions and drought huznrd. If the storm
incidence is high in any given area the moist.ure content of the soil
is likely to be high when ruin occurs and run-off muy result from even
light showers. If the int.erval between storms is great, however, the
soil will be dry and no run-oft' will result. from ruins of low intensity.
The -frequency factor also is significunt us an index of tllt' drought
hazard. Crop failure t.hrough drought necessnrily exposes cultivated
land to the erosive force of the wmd, and this clinlatic risk cmmot.,
therefore, be dissociuted from t.he general erosion problem.
Finuliy , the ureal chllr,wteristics of rainstorms ure exceedingly .im­
portant. The center of a storm ma,y be very smull. and the nature
and extent of the erosional damuge may vary considerably, the dam­
age to uny given urea depending Dn what portion of the total storm
structure h~~ppens to pass over t.hat area. The size und position of
3
Italic n umbers in parentheses refer to Literature ('Ited, p. 29.
l I'E!<!<5VLYA!<1.A DEP.\ltnIE!<T OF FORESTS .<!<D ,,',HERE, Dn'ISIO!< OF llVDROGR.<PHY. THE I'LOODS OF
MARfH 1936 I!< PE!<!<SVLVA!<IA. 121l pp., illus. Harrisburg, .Pa. 1936. [Processed.] (Prepared in coopera·
tion with the L. 8. Geological Surwy.)
RAINFALL CHARA(;TERBTICS AS RELATED TO SOIL EROSION
3
the storm is also particularly critical in relation to floods. If the
storm covers an entire wutershed the run-off will be much greater
than if only a smull portion of the drainnge basin is affected.
A. realistic and practical study of the relationships betweeu precipi­
tation and erosion necessitates the analysis of rainfall da,ta in terms
of the intensity, duration, frequency, and aren factors. Although
rainfall records are much too short to be wholly satisfactory and al­
though rain gages in tIns country are spaced much too widely, a vast
amount of material, which will greatly clarify €-!'0sion and conserYa­
tion problems, has yet to be extracted from the e;'-1sting data. In
this study an nttempt will be made to demonstrate the feasibility of
handling these data so as to yield pertinent information for estimating
erosion hazards.
THE PROBLEM OF ANALYZING PRECIPITATION DATA ~
ClimatologistS have, in the past, mainly coneerned themselves with
monthly and annual precipitation figures. "While these quantities
have proved to be useful in many ways, they actually mask the yerv
precipitation characteristics that are of critieal importanee in all
soil-erosion problems. ~<\s an examination of hydrologic literature
shows, daily and even hourly rainfall figures should be unalyzed.
For example, the fact that 10.36 inches of rainfall occurred at Dayt<>n,
Ohio, during ~Jareh 1913 does not reveal the very significant infor­
mation that 9.60 inches of this nmount occurred in 5 days, causing
serious flood tmd erosion conditions (2).
Both monthly nnd annual rninfnll amounts are a eomposite of in­
dividual stonu amounts. During 1908 the precipitation totnis
recorded nt many of the stntions in eastern and cent.rnl Oklahoma
were more than twice the mean amounts; Yf.1t, if the rainfall amounts
resulting from the tJrree storms of May 23, June 5, nnd October 20
were subtracted from the rainfall records, the annual precipitntion
would not be excessive (5, pp. 30-31).
The stoTm itself is the natural and logical unit in any consideration
of precipitation. Vnfortunately, storm patterns can be determined
only where there exists a closely spaeed network of nun gages which
are self-recording or at which simultaneous observntiOI{s are mnde
at very short intervals. However, it is possible to de,~elop a method
whereby records from indh-idual stations, taken at a point, can be
interpreted to yield generalizations that mn,y be applied to entire
areas.
Rainfall maps plotted for 15-minute and X-hour periods from
simultaneous records taken at nearlv 200 raininll stations of the
Oklahoma Climatic Research Cen~er ;md the }~-hour maps prepared
at the Muskingum Climatic Research Center have made possible a.
better understandin~ ~~ the nature of rainstorm morphology. Hence,
data obtained at inJividual stations can, be interpreted more accu­
rately (10). Two types of storms have been identified: Intense
local showers of short duration and less intense general storms of
long duration.
'In this and suct-eeding !'ection5 the meteoro,ogical interpretation of the data has been supplied by
Benjamin HoWuau of the Climatic and Physiographic Di\"ision.
4
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
CONTRASTS BETWEEN LOCAL AND GENERAL STORMS
The contrast between these two types of storms has been discussed
in other publications (3, 10). It is sufficient here to point out their
differences from the point of view of minfa.ll genesis and pattern. In
geneml, the intense local showers of short duration are c&.used by
convection in the atmosphere. TIllS convection may be produced in
several ways: Through the interaction of cold air masses with Tm
(Tropi('al Maritime) air bodies that are characterized b~Y a thermo­
dvnamic instability; through insolational heating in the lower levels
or c(,oling aloft. either of which causes superadiabatic lapse mtes in
tropical air; through orographic lifting of convectively unstable air;
or through a combination of these and other factors. The general
storms of longer duration are not dependent on the presence of un­
stable air; rather are they caused by some combination of fronts
wherein moist air is forced aloft over a denser air body and, after
reaching the condensation point, produces rainfall. However, super­
imposed on this general precipitation there may be convective showers
resulting from the lifting of unstable air.
Corresponding differences ~n rainfall pattern are displayed by these
two storm types. ConvectIOnal showers produce a more hetero­
geneous pattern within a small area than 00 general storms. Also.
convective precipitation affects a much smaller area than do general
disturbances.
The storm of March 12-13, 1937, charted at the Oklahoma Climatic
Research Center. illustrates these differences in rainfall genesis and
pattern. On the morning of March 12, 1937. a mass of Pc (polar
Continental) air occupied the entire northern Great Plains region
(fig. 1). The southern boundary of the Pc air lay oriented as a quasi­
stationary cold front through Oklahoma and Arkansas and along the
southern boundary of Tennessee. Tg (Tropical Gulf) air occupied
all of the Gulf States. In the western part of the United States,
NPp (neutralized or modified Polar Pacific) air was present, limited
by an occluded front extending from Arizona into Oregon.
The frontal positions had not changed materially on the morning
of March 13. There was, however. a very definite increase in the
intensity of the dome of Pc air centered north of North Dakota. This
clearly indicated that the polar air would push southward into the
Gulf of Mexico.
On March 12, at 6:45 p. m., central time. rain hegan to fall in parts
of Kingfisher and Logan Counties, Okla. The rainfall maps in figure
2 show the actual amounts of precipitation b.v%-hour intervals. The
rain was associated with It wave on the cold front that had retrograded
into the research area (fig. 3). The resulting thunderstorm produced
several centers of high intensity during the next few hours. One of
these centers moved across the research area (fig. 2). It is of interest
to note that although the same general meteorological conditions
affected all the area, only tlie eastern half received any rainfall.
By 1:30 a. m., 1'1arch 13, the cold front had passed to the south,
but a drizzling rain began to fall over the greater part of the area.
The rainfall intensity averaged about 0.05 inch per hour. The pre­
cipitation pattern became relatively homogeneous as compared with
RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION
5
March 12, 1937
...
30.
7 A.M. C.S-T.
March 13.1937
Npp
Modified Polar Pocific All
- C o l d Front
Pc Polar Continental Air
Tg
Tropical Gulf Air
-----Occluded Front
FIGURE I.-Synoptic weather maps of the United States, March 12-13, 1937.
6
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
LEGEND
• • •"
o
FIGURE
2.-Half-hourly precipitation for storm of March 12-13, 1937, in the
eastern part of the Oklahoma Climatic Research Center area.
RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION
FIGURE
2.-Continued.
7
8
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
-ColdFrcnI
- - - Oct:bied Front
a.-Detailed synoptic weather maps of Oklahoma and surrounding States,
March 12-13, 1937. The area covered by the 200 rain gages of the Oklahoma.
Climatic Research Center is shown by the shading in the center of the map.
FIGURE
the pattern produced during the first part of the storm. As the Pc
air pushed farther southward and colder air invaded the area, thr light,
rain changed to a light snow. The storm continued until 3:00 p. m.
During all but the last few hours the pattern remained essentially
the same as that shown in the last map of figure 2. As the storm
left the area, however, the rainfall distribution became spotty, and
the total amounts recorded became insignificant.
This sequence of rainfall maps illustrates certain contrasts between
local and general disturbances. From the point of view of the soil
9
RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION
conservationist, the fact that the st.orm types differ in areal extent,
duration, and intensity is significant. Local storms rarely produce
simultaneous precipitation over an area of more than 1,000 to 2,000
square miles (11), whereas general storms not infrequently produce
simultaneous rainfall on an area in excess of 100,000 square miles.
In addition, the latter storms are generally characterized by far
gentler intensities and by considerably longer durations.
INTERPRETING INDIVIDUAL STATION RECORDS
Figure 4 shows the cumulative rainfall for the storm of March
12-13, 1937, at stations A, B, and C shown in upper left-hand map
of the first part of figure 2. It should be noted that although A and
B are only 13 miles apnrt the rainfl1l1 curves are dissimilar because the
local storm center happened to pass directly oyer A, whereas the
9
MT
0
1
2
5
4
3
or:: =:
'8
=.o;c :"'-t
,~-\
9
10
11
MT
1
Stations: ,----,-,=4
2
3
4
5
B
6
7
~
8
9
lC
------c
FIGURE 4.-Cumulative amounts of rainfall at three selected stations CA, B, C)
for the storm of March 12-13, 1937. For location of these stations see the
upper left-hand map in the first part of figure 2.
record at B was determined only by the margin of the storm. The
curve for C is intermediate, since the storm center passed only a short
distance awav.
It. is clear" from these examples that an individual station record
does not yield direct information as to the areal characteristics of any
particular storm. The location of the recording station with reference
to the storm structure determines what any particular rainfall record
will be.
However, within a given climatic region in which the surface con­
figuration is moderately homogeneous, the particular path a storm
takes may be considered to be a random event. It follows, therefore,
that if rainfall observations are made for seyeral years at anyone point,
a Q'reat number of rainfall samples from different portions of different
st~rms will be obtained. Each additional sample at such a single
station will make it possible to obtain a closer approximation of the
147950 0 -3ll--2
10
TEOHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
rainstorm characteristics for the homogeneous region. Finally,
enough data will have been accumulated to allow the making of accu­
rate generalizations regarding such factors as storm frequency, inten­
sity, and duration. 'While such ~eneralizations do not, of course,
provide information regarding specific individual storms they do give
a necessary picture of the mean storm characteristics of the region
and the range in such characteristics as normally experienced.
AREAS AND STATIONS SELECTED FOR STUDY
In this study the three areas selected for investigation were the
southern Great Plains, the southern prairie grassland region, and
the mOlmtain-Piedmont-coastal area of West Virginia and Virginia.
FIGURE
5.-Station locations on base map showing climates of eastern United
States according to Thornthwaite's classification (8).
In the Plains region, Amarillo, Tex., Ilud Dodge City, Kans., were
chosen for analysis. Both lie in a. semiarid meso thermal climate
(fig. 5). The adjacent prairie region is represented by Wichita,
Kans., Oklahoma City, Okla., and Fort Worth and Dallas, Te..'t.
Fort Worth is situated approximately on the boundary between the
·moist and dry subhumid mesothermal climates; the other three
stations are located in a moist subhumid mesothermal climate (fig. 5).
The six Plains and prairie stations lie in what are normally three
different climates, but the surface configuration at all these stations
is essentially the same-open plains or prairie.
RAIXFALL CHARACTERIRTICS Ai; RELA'fED TO SOIL EROSION
11
The three eastern stations selected are situated in the same general
climatic province ~l1t ~ areas that are topographicall:r dissimilar. All
three Lu,ve a humId clm1ate, and all are Ileal' the mesothennal-micro­
therm",1 boundary (fig. 5). Elkins, W. Va., is located in the Appa­
lachian Plateaus, just west of the Allegheny Front; Lynchburg, Va., is
situated in the Piedmont; and Washington, D. C., is on the Atlantic
Coastal Plain.
The analysis of rainfall dnta for the six Plains and prairie stations
should reveal whether the contrast between the semiarid and subhumid
climate is, in ternlS of rainfall, simply one of rainfall amounts or
whether specific rainfall characteristics themselves are different in the
two regions. In filly case, the quantitative detennination of these
charncteristics should aid in developing erosion-prevention methods
applicable to wind erosion on the Plains and gullying and sheet wash
on the prairies. Similarly, study of the data for'the eastern stations
should not only make it possible to detennine what effect surface
configuration has on precipitation but should also accurately depict
rainfnll characteristics in this area. In all three areas the problem
is therefore twofold: To depict accurately the nature of the rainfall;
and, if possible, to elicit climatic and meteorologic generalizations,
which may then be utilized in studying the rainfall characteristics of
still other areas.
TYPES OF ANALYSES
UNDERTAK~N
Since rainfall intensity, duration, and frequency are the three ele­
ments of precipitation of most immediate and direct concern in soil
conservation, it is of practical significance to analyze rainfnll records
in these terms and to determine what differences, if a.ny, exist from
region to region. The seasona.1 variation in these components should
be emphasized because of the relationship the crop calendar bears
to erosion hazard. The time of plowing is significant because during
this period the soil is particularly suscept,ible to erosion through
sheet was11 and gullying. Similarly, inlmediately arte·r harvest, wind
and water can wor~ ",ith greater efficiency in engendering erosion
than while the land IS protected by a crop cover. If, in terms of the
agricultural regll1e, the land is exposed during periods that coincide
with those of ma)..imum climatic erosion hazard, this fact should be
re&1ized and adjustments made wherever possible.
In the analvses that were made the units used were either small
time interyals:"""'-15 or 60 minutes-or the stonn period itself. In
most analyses the data for all nine stations were subjected to the same
treatment; but in a few, the mah'rial for the three eastern stations
was handled in greater detail.
DATA UTILIZED AND METHODS OF COMPILATION
The length of record that could be used was defillitel~' limited, since
automatically recorded rnin-gnge data were necessary to provide the
detailed infonnation required. The Dallas record, 22 years in length,
was the shortest. The other stations had records in excess of 30 yea.rs.
The years covered for each of the nine stations are shown in table 1.
12
TEOHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
TABLE
Station
Period co,'·
ered
Dodge City, Kans ••• _. ____
Fort Worth, Tex .••••••.••
Oklahoma City, Okia ••.•.
Wichita, KaD5••.•• _......
Aml\rillo,Te:r. ............
1894-1935
1899-1935
1900-1935
1903-35
1903-35
I.-Length of station records
Years of
record
utiUzed
42
3i
36
33
33 Station
Washington, D. C ••••• •••.
Lynchburg, Va.' ••••••••••
Elkins, \\'. Va•••••••••••••
Dallas, Tex ................
of
Period coy· Years
record
ered
utiUzed
1905-35
1902-33
1905-35
1914-35
, For Lynchburg the 31·year record coyered the period July 1902 to June 1933, at which time
was reduced to a second-order one and the tipping·bucket gage was remo,'ed,
31
31
31
22
th~
station
Data were extracted from the triple-register sheets kept by the
United Stutes Weather Bureau (Form 1017). For the occasional
times that gages were out of order, corrections were made by inter­
polating from stick measurements; and for snow the stick measure­
ments, properly reduced, were used.
"Traces" o( precipitation were excluded from consideration unless
they occurred in an hour immediately preceded and f".)llowed by meas­
urable amounts (0.01 inch or over). Since any such included trace
may have contributed to the recorded precipitation of the hour fol­
lowing, for the purpose of calculating duration it was iuterpreted as
being equivalent to measurable precipitation,
Since dehiled areal storm maps were not available, an arbitrary
definition of "storm period" was used. For the purposes of this
study a storm period was defined as being a, period during which meas­
urable precipitation occurred during consecutive clock hours. The
meteorological concept of a storm is fundamentally related to the
conditions that cause rainfall, In many instances the same meteoro­
logical disturbance produces successive periods of precipitation thllt
are separated from one another by an hour or two; in other cases sev­
eral meteorological storms may yield a continuous rainfall record.
In any nongenetic definition, there is, therefore, an inherent bias that
cannot be eliminated. In calculating storm durations, a storm was
taken as starting at the beginning of the clock hOllr during which
precipitation was first recorded and ending at the end of the last clock
hour during which precipitation occurred. This method of deter­
mining storm figures may be open to some criticism, but it is deemed
to be sufficiently accurate for use in connection wit.h problems of soil
erosion.
ANALYSIS OF MONTHLY AND ANNUAL RAINFALL AMOUNTS
It has already been stated that monthly and aIlnual rainfall figures
mask the specific rainfall characteristics that are of practical im­
portance in soil conservation. The magnitUde of these amounts is
really determined by the number of storms that occur and the amounts
falling in these storms. Of the nine stations whose precipitation data
were analyzed, Elkins, W. Va., had the highest mean annual rainfall
for the period selected (47.9 inches), and Dodge City, Kans., had the
lowest mean annual amount (18.3 inches), There is a corresponding
difference in the storm incidence at the two stations; Elkins experi­
ences an average of 195 storms per year, and Dodge City receives
only 77.
13
RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION
Figure 6 shows the mean sea­
sonal storm frequencies for an the
stations. Fort Worth, Amarillo,
and Dodge City all experience an
average of 77 storms per year
(table 2). Yet the nnnual preci­
pitation at the three stations is
different, Fort Worth receiving
32.0 inches, on the average, as
against 20.7 for Amarillo, and 18.3
for Dodge City. This is due to the
fact that the storm amounts at
Fort Worth are higher than those
at Amarillo, and Amarillo, in turn,
usua.l1y receives more precipitntion
pel' storm than does Dodge City.
For example, over 11 percent of the
storms occurring at Fort \Vorth are
in excess of 1 inch; the cOlTespond­
ing figures for Amarillo and Dodge
City are 4.5 percent nnd 4.1 per­
cent, respectively (tnble 3).
The minfall regimes and the
meanmonthlv and annual amounts
at the various stations may til us be
ficcounted for in terms of storm
incidence and amounts. At the
three eastern stations-W ashing­
ton, Lvnehburg, and Elkins--tlie
rainfall is normnllv in excess of 36
inches annually find is well dis­
tributed throughout the year, with
a slight summer maximum (fig.
7). The storm incidence is COlTe­
spondingly high and fairly uniform
from scason to senson, a slight
maximum OCCUlTing in the sununer
(fig. 6 and table 4). With respect
to these tIll'ee stations, the,storm
frequency is highest at Elkins
(195 pel' year) find approximately
the same at Washington as at
Lynchburg (136 and 134, respec­
tively). Washington actually
receives more precipitation than
Lynchburg, however, since the
storm amounts are somewhat
higher.
In contrast to the conditions
in the eastern area, the prairie
region-represented by . Da.llas,
Fort Worth, Oklahoma Cit.y, and
Wichita-rel'eivesfrom 29.0 t033.9
inches of precipitation per year.
WASHINGTON
·, o.c.
LVNCHBURG
VA.
ELKINS
W.VA.
-
,
,
.­
,
•
~
.,
Ii
I
0
,
DALLAS
FORT WORTH
OI<LAHOMA CITy
TEX.
TEX
Of(LA
0
,
'0
!,,
·, ,
WICHITA
KANS.
·
•
·
AMARILLO
000 GE CITY TEX
f(ANS ,
•
.
c
.
6.-Mean seasonal storm fre­
at each of the nine stations
indicated. The exact years covered
for each station are sho\vri in table 1.
FIGURE
quencie~
14
TECHNICAL BULLETIN 698, U. S. DEPT. OE AGRIClTLTITRE
L1NCHBURG.
WASHINGTON, 0 C
•
II
I.
II
FIGURE
VA
El"IN'
VA
-
1.1
I
7.-Mean monthly precipitation at each of the nine stat,ions indicated.
The exact years covered for each station are shown in table 1.
with the maximum rainfall occurring dUl"illg the spriu1! iUld early sum­
mer (fig. 7). A greater number of storms is experienced tit all these
stations during the spring than at any other season. with tIm except.ion
of Wichita, for which the spring and summer incidence is the same
(fig. 6). Only Dallas, however, receh-es its maxinlUm storm alllounts
during the spring; Fort Worth and OkIu,homa City displny nutllllln
maxima with regard to storm nmoLLllts, und Wichit:l experiences
approximately the Stulle mnxinllull nmolmts ill summer anel autumn
(tnble 3).
AllUU·illo and Dodge City, located in the spmiarid Great Plnins.
Ita ve the lowest rainfall amounts of all the stations studied. a nel becaus('
of the higb mte of e,"npomtion the rainfall is frequently deficient as
fttr as agriculture is concerned. The menll mUlual precipitntioll at
both stations is llllder 21 inches, and their minfnll regimes tl1'l' charac­
terized by SUllllller maximu und winter minimu (fig. 7). Thl' SUllUllN
uUlXima are particulnrly well marked. since both storm incidence and
storm amollnts nre greater at this season than nt any othl'l'; the winter
minima are likewise distiuct, storm frequencies and amounts displaying"
.their lowest vnlues during this senson (fig. 6 and tables 3 and 4).
15
RAINFALL OHARAOTERISTICS AS RELATED TO SOIL EROSION
RAINFALL-INTENSITY FACTOR
The importance of the rainfall-intensity fact.or has been recognized
lor some time, particularly in its bearing on flood hazard. The Miami
conservancy district (6) study of rainfall in the eastern United States
and that by Yarnell (12) with reference to the entire country have pro­
vided intensitv-e~-pectancy figures for various time units that bring
out the general variations from region to region. The fact that inten­
sities "Vary greatly from season to season, however, has not been con­
siiered previously. With regard to both flood and erosion problems
this seasonal variation is of practical significance.
Of the areas studied, the eastern stations experience the highest
intensities, thm,e in the prairie region are intermediate, and the lowest
intensities occur in the semiarid Plains area. With reference to all
except one of the stations subject to scrutiny, the relationship holds
that the season of mu...ximum rainfall is also that of maximum precipita­
tion intensity. Oklahoma. City is the sole exception, for there the
spring precipitation exceeds the summer amotmt by slightly over 1
inch, whereas the maximum intensities are e~-perienced in the summer
(fig. 8).
At Washington and Lynchburg, rainfall intensities are highest
during the summer and early autumn months (table 5). The magni­
tude of the contrast in intensity from season to season at these stations
may be seen from figure 9. ~ Elkins, unlike the two other eastem
stations, experiences its highest intensities in the summer only.
Probably this is because the extremely intensive general storms that
affect the southeastern Coastal Plain ill em'l:; autumn do not pene­
trate westward into the mountainous area in which Elkins is located.
All the stations in the southern Plains and prairie region have their
ma~-imum rainfall intensities in the summer, with the absolute lllten­
sity values decreasing from enst to west and from south to north
(table 6). Winter intensities fire extremely low except at Dallas and
Fort Worth, the two stations nearest the Gulf and the source of
Tg air.
...
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=:
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O... r 100
S.-Precipitation amounts falling at specified intensities, showing seasonal
variation at the three stations indicated. The exact years coyered for each
station are shown in table 1.
­
FIGURE
16
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
4
LYNCHf,VAI
In order to obtain informa­
tion
rega'rding intensities during
I;; •
,
short time intervals the maxi­
~ mum 15-minute rainfall inten­
~ ~ ~ ~ , '.
I; sity was recorded for every storm
I· ; ....
•
,
'l': ~~ :
that occurred, and these Were
~
Sl
~
en
tered in frequency tables.
,
~%, ;;/ r:%~ b:; (See table 7 and fig. 10.) The
~
;.: results obtained corroborated
t;;
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the generalization already made
the tn.bulation of storm
/
~ ~ ~ ,~ ~~., ./,~ ~ ~~ from
amounts by seasons, namely,
WASHINGTONlD. C.
that the highest intensitie~)Occur
at the eastern stu,tions and the
lowest at the two Great Plains
stations, Amarillo and Dodge
City, The explanation of these
~
~
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c"
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be fonnd in the fact that high
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rates of rainfall are almost in­
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vnriably associated with con­
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vective storms originating in air
~,
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masses
of tropical-ma,rine origin.
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The Tm air that frequently in­
,', ~'
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~~. :? ~'/ f%:~0'"/, ~:;:; ~
cally
always has Il. higher total
~: r:?:
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moisture content than thnt, for
W V4
e..xumple, at Amarillo or Dodge
City, and is thus able to produce
a greater amount of rainfall
whenever the meteorological
or
t
forces necessary to relettse the
...
II
wn.ter vapor come into play.
::.:.
From the data pertaining to
~~:':::: ~ ~~~ If.::=: III [1~ /?:.
15-minute
ma).:imum intensities
$
F"
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it
is
possible
to calculate the
,I .. , .,.,., J
~I-iii! ::::
;.::2
seasonal
intensity-expectnncies
I ;;;:; " for this interval at anv one of
~
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i
the stations. Tllis provides a
x~
~ ;~ " f/~~ ~
needed
refinement of the method
~;
I;?
b;
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,0, Yarnell
(12) used for calculating
p~ "
%
~
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intensity-expectnncies Jor sbort­
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v~
period falls. since the seasonal
t::" '.~: z:~. ~
contrast
is thus brought out.
'/
~
:~:
~
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f
;-' '/ l~ ~
~ The intensity-expectnncy curves
for Lynchburg for the four
seasons are shown in figure 10,
LEGENll
Rote in Inc;:tles p.r Hour
the 15-rninute intensities beiJlg
~ c:::J m@@ ~ _
plotted along abcissas and the
..O)...JO jJ",20
.21.,aO
51.' 00
O"edGO
expectancy in years along ordi­
FlGUR.E 9.-Precipitation amounts falling nates.
The magnitUde of the
at specified intensities, showing monthly
variation at the threEo stations indicated. differences in e.."'tpectancy from
The exact vears covered for each station season to season may be illus­ are shown in table 1.
trated by considering'the expec­
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AMARILLO
00
100
IW
140
100
120
140
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PRECIPITATION
0
1-3
o
.40
£0
80
100
120
140
160
~ln~~1)
JO.···Expcctnncy cllr\'t~f\ for IIlnximlllJl 15-millllte RtOrlli lunountll uf rninfllIl Ilt the nine stations indicllwd. The four curves
illdit'IlW till.' \'nrintioll in CXIJI'clullcy fronl ;;e!l.~(m to season. Th(' {'Xllet }'I'ltrii {~o\'(~md for euch statioll urc shown in table 1.
FII1PIIE
o
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-1
18
TECHXlGAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
taucy of receiving 0.44 inch or more ill a I5-minute interval during
elldi of the four seasons (tabl( 7). In the summer this amount will
be received on the average four times et1,ch seasoll; in the spring it is
t.o be eA"J)ected to ocem- npproximat.ely twice every 3 years; the autumn
expectaucy is once E.wer~T 2}~ yenrs; and dm-iug t.he wlllter this amount
would be recorded on the nyemge only once every 22}f years.
With regard to 15-millute periods, in 1111 the llI'ens studied the rain­
fall intensity is highest during the summer months nnd lowest during
the winter (fig. 10).6 Certain cOlltrnsts in relati\'e positioIl appear,
however, when the autumll Ilnd spring cunes lire considered. 4~t t.he
foUl' prairie stations the spring nnc1 summer intensities /1.re of the same
general magllitude. the spring \Ttllues being only slightly less than
t,hose for the summer. At Lyuchbmg" IUld Elkins. in the eastern
area, and at Amarillo ltnd Dodge City. in the Pll1ins. there is n marked
difference between SUlllmer and spring 15-minut.e intensities, and the
tHltunm IUld spring intensity-expectancies are II ppro:-.:imn.telY t.he
same. The WashingtOll curves, while indicl1ting 11-11 appreciable
discrepnl1c~~ between HutU11ll1 and summer intensit.y figures. lH~\Ter­
theless displn,y autumn \'nIues distillcd:v greatpr than those for sprin(7.
This is to he attributed to the marked effl'C,t of intensive O'ener~1
a·utumn storms at Washingtoll.
"'
The n.bsolute ] 5-minut.e intensit.y-expectllllC~' figures corroborate
t.he genernlizatiolls made from the general intensity <,harts (fig. 10):
The Ylllues for this short-peIiod intensity as well Ils for intensities of
longer intervnls nre greatest. in the east.em area; in the wegt.em Ilren
they decrense from east to west and from sout.h to north. These
relfi,tionsbips demonstrate that where rninfall int.ensities are hiO'hest
with refere..TJ.ce to periods of sufficient length to be measured in h~urs
the shorl,-tim0 intensities will also be at a mnximum.
'
RAINFALL DURATION 7
Rainfall intensit,y and duration determine the amount of predpitn­
tion in any given storm. Two storms-one short, locnl, and produc­
ing high-intensity fnlls, the other of long duration, geneI'n}, Ilnd pro­
ducing low to moderate intensities-may yield the snme amount of
rninfn11. Since genera] storms nre usunll}Y characterized bv 10w­
intensity precipitation nnd local showers by high rntes of rainfnll,
there is n general inYeTse relntionship between rninfnllintensitv and
rninfl111 durntion.
•
It nccorclingly obtnins that wherens the stntions studied showed
illtensit~- maxima for th(' Bhort spring Ilnd summer :;:;torms, it is the
low-intensity autumn llnd winter storms that nre of the longest durll­
tioll (fig. 11). The renSOIl for this is e\-ident. C'y<,lonic stonns v..-ith
prolonged warm-front precipitation predominnt,e in full and ,\inter.
Hnd local convective 511ow('1's nre chn:rncteristic of the spring and
Slimmer seasons. These fncts are in tum explained b~T the frequencv
of iIwasions of tropical and polar air and the modification of theIr
thermodynamic properties I1S t.he sensons chnnge. As t.he SUll
disappean:. from the polar regions in Odober there occurs a southwl1rd
displacement of the poIn!' front. In tempernte latitudes this results
in a correspondingl:,- greater durntion of occupnncy of polar air. As
a '\·hi1(, thf'~(,_ ~xf){>(.'taIl(·~· ('un'rs cr(\ most nrarly securn(r in tht:'ir low(,r portions, tht'v are still Sigllifi('l.lDt.
in th~ir upPt'r rnn~~ sinCt' no e.<pectRncy excet'ding I h~ numher of years of record was uSt>d•
• "Rainfal! duration" as used in thi, !'ection r~f~rs to the length 01 storm periods (lnd not to the number of
bours. by weeks or months, during which precipitation occurs. For eXlUDple, compare table8and figure II.
RAINFALL CHARACTERISTICS AS RELATED TO SOlL EROSION
.
19
.------r---~--r-----__,
WASHINGTON,O.C.
LYNCHBURG, VA.
ELKINS,W:VA.
~~---~-+---~-~-V7~-__1
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fORT WORTH, TEX, OKLAHOMA CITY, OKLA
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6-12
12-24
Hours
Hours
..
_
Over 24
Hours
n.-Precipitation amounts falling in storms of specified duration show­
ing seasonal variation at the nine stations indicated, The exact years covered
.
for each station are shown in table 1.
FIGURE
20
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
the sun returns to the polar regions in Ivfarch, more frequent invasions
of tropical air, characterized by nn increllsing tbermodynnmic insta­
bility, occur. At }i~lkins, for example, 31.5 percent of the winter pre­
cipitation o~curs in rains thnt persist for 24 hours or more, wherens
during the summer, when intensities nre the highest, only 3.2 percent
of the precipitation occurs during rninfalls lasting thnt long.
In absolute figures, more precipitntion occurs durin~ storms of long
duration at the three eastern stations than at those 111 the soutl!('rJ1
Plains and prairie regions (fig. 11), because storm incidence is higher
during the autumn and winter in the Yirginin-'Vest Virginia nrea than
it, is in the Texas-Oklahoma-Kansas urea.. s In both areas what pre­
cipitntion does occur during the winter and autumn falls mainly in the
storms of longer duration.
.
Table 9 shows the distribution of rainfall amounts, by hours, within
storms of specified durations. With reference to the data for Wash­
ington' 70 percent of the summer Plecipitation oecurring in storms of
2-hour durn.tion was concentrnted in the first hour, as wns nlso 61
percent of the sprul{$" precipitation for storms of this length. For
2-hour storms occurrmg during the other two sensons, however, thE'
storm nmounts are fnirlv evenh- divided between the first nnd second
hour. Since one of the characteristics of local showers is that the
highest rate of precipitation occurs during the enrly portions of the
storm. these dnta again illustrnte that spring and summer are chnrac­
terized by local convective disturbances, whereas the general storms
occur mainh- in the autumn und winter. The data for the distribu­
tion of rairlfall amounts in 2-hour storms durin~ the autumn lind
winter should not be interpreted ns indicuting that the ~eIleral storms
producing these amounts lusted only 2 honrs. Whut is signified is
that the recording stntion happened to be peripheral with respect to th(>
storm strncture, and the"efore rain wus recorded for only a 2-houl' period.
There is no regulllrity in the hourly distribution of rninfnll nmounts
in storms of long duration (tn.ble 9). The hour of maximum precipi­
tation for anyone stOI'll1 depends solely on the location of the rain ~uge,
or in other words on what particular part of the storm is sampled. If
the storm pattern were symmetl'icalalld the mi~ration rnte constaut,
and if the storm center pussed directly over the ~a~e, a mu)o:imulll
would appear upproxhnately at the mediun hour; but becnuse of thE'
variations in the path of the storm Hnd the recognized complexities
in rainfall pattern, such a distributioll could hnrdl~~ be e)o..lJected.
LENGTH OF PERIODS WITHOUT PRECIPITATION
Protracted periods without precipitntion make the soil particularly
susceptible to removal by rain waters or wiud. It is eleur, therefore,
that rainless intervals of long extent engender erosion.
Undoubtedly drought, particularly protracted drought, has contributed greatly
to the decline of the watershed value of certaill areas by kiI1ing off !'OIJle of iln'
plants or limiting their growth and reducing their den;;;ity. The death or clilllill­
iRhed growth of the plant Illeans, in turn, a general depletion of the plant CIlYN
and leli" phy>,ical protection to the soil. During droughts, the phYliieal propertil'H
of the Hoil are Illodified by exce.o;"ive drying, its power of cohesioll is IP""l'II pd,
and it becomes more :m;;ceptible to the force:; of wind and watpr. The stag!' i,;
thuR set for destructive pros ion (J, p. 814).
It is therefore desirable to determine how periods without precipi­
tation vary in length from season to season and from urea to urCH.
, The greater frequency of winter storllls in the ellstern l-nited States is due to tbe nUlllerous "'Il\'e llis·
turhances that generally develop on the polar front under the influence of tbe Bermuda anticydone.
RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION
21
By compiling such drought-expectancy figures the basis is laid for
{\\--aluating this particular climatic risk in various regions und for
instigating effectIve pr~autionary measures.
The allllual expectancies of rainless periods for Amarillo, Dallas,
Lynchburg, and Elkins are shown in figure 12. The plotted points
we10 fitted by straight lines and, since the curves were plotted on a,
semilogarithmic base, and the fit was good, au eJ..-ponential relation­
ship is indicated. (Compare fig. 12 'with table 10.) That this expon­
ential relationship does not strictly hold for the lower portions of
the curves is evident since the x- and y-intercepts must both be at
the origin. Similarly, since 45 r-----,---,:---r-,----r--u--,-,...,TTT'1
it would be impossible to obtain an alllluale)..-pectancy of a rainless period greater 40 1---t---1i-+-t---I--+-+-+-+H+I than 365 da:vs, the e)..-ponen­
tial fllllction camlOt truly apply in the uppermost part 35 I----+--+-I--+-+---f---f-~*I of the complete curves. Curves covering the com­
plete ordinate range would ~ 30 I - - - - + - - - t ­
therefore really be asymp­ 0
totic to the x-a..us at their III
base and to a line parallel ~ 25 1-_-+_ to that a:ris in their upper ~ portions. This upper as- a: ymptote would, for the vast ~ 20 1----7L--++!-t--~ majority of stations, lie con- § siderably below the 365-day ~ value because of meteoro- ~ 15 1---f----7!'---'-T+_ logic limitations on the
maximum length of rainless periods. More climatic data.
10 ~--7"''---,~i-+-+--+--+--l-''-+-+'-i and further meteorologic analysis arenecessary before the upper as:rmptotes can be determined. Therefore only the central portions of the curves have been plot0 ' - - _ - - '_ _'--~.l.-_..J.___'__"__'_~ ted in the figures, and within
1025
50 .75 I
2
4
6 8 10 this range the exponential
FREQUENCY (Yeors) relationship holds sufficient- FfGUR~ 12.-Frequellcy of railll~s ~ri?ds of lywell to warrant its havinO' s~Clfied length at the four stattons lll<?cated. Of
'1he exact years covered for each RtatlOll are
· th
b een use d In e process 0
showll ill table J
curve fitting.
.
.
Amarillo and Elkins are the two extremes for the nine stations.
The Lynchburg curve is very sinlilar to tha,t for Washington. The
curves for the five remaining stations cluster about that for Dallas.
Since the data used in plotting the curves in figure 12 are based
on precipitation datn of 22 to 3a yeltrS ill length, the simple annual
(once per year) expectancies should be 11 fnidy relinble index of com­
parison. At Elkins this annual e)..-pectancy is 11.5 consecutive rain­
less days; at Lynchburg, 16.5 days; at Dallas, 22 days; and at _~a­
rillo, 32.5 days. Amarillo experiences periods without rain which
are three times as long as those occurring at Elkins, the a: 1 ratio
<.) ~
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If'
~ 6 810 .10
Hca.'lO!1Il1 drought CxpcctILIIC.'· Ilt tlte ei/{ltt statiulI~ illdicated.
;..
o
!:::::
....
o
D~LL"S•••T~l':
,\EX.
FREQUENCY CY••<O>
Ff(JtJII~; 13.
rn
£ ~ I...-l-­ ~
It OKLAHOMA CITY" OKLA,
25
r6
w
fill Illil li ~w~
WI 11 I 1'11:1111I V I I YfO~TH;.
~
10 ~
II J
.25
.50 .75 I
•
6 810
c::
~
c
(;;
UAINl<'ALL CHAUACTERI8'fHJS AS RELATED TO SOIL EUOSlON
23
holding in genernl for the longer rainless periods Lecnuse of the linenr
nnture of the plotted curves in the higher expectnncy mnge..
Just as storm frequency varies froll. season to season, so also does
the length of the intel'storm perio~s. The sensonnl expectancy
curYes for Washingtoll (fig. 13) indicate that periods without precipi­
tation nre longest during the autlUllll, intermediate ill the sprmg and
winter, and shortest during the summer. The same relationship
holds for Lynchburg (fig. 13). Elkins, likewise, has the longest intel'­
vals without precipib1tiol1 during the autumn; but the shortest periods
occur during the winter (fig. 13),'
A.t the four subhumid stations-Dallas, Fort 'Yorth, Oklahomll City,
and vVichita-spring is the senson when periods without precipitation
Hre shortest (fig. 13), The mH..x imum nmount of precipitation nlso
occurs ill spring, specifically in the month of :Mny, At both Dnllns
and Fort vVorth the drought hazard during the summer, autumn,
Hnd winter is appro:..:imntely the same, During the will tel' numerous
storm:; generillly de\'elop in the Gulf of ~Ie:..:ico dong the poluI' front,
nnd these frequently extend their influence some disb\llce northward
from the Gulf. OklnhomH City nnd Wichita lin' suffi('ienth' fnl' r('­
moved to receive winter precipit'ation from these storms It'ss fr~~qupntly
t han Dallas illld FOl't Worth.
The relutively short intervals without rainfall dming tlIP spring lIrc
ill lI(,t'ord with II C'onsiderutioll of thc lIleteorologicul [ore('::; thll t
gellemlly opel'llte in tlus region at thn t scasOI!. The poInl' front is
beginning to be displnced 1l0rthwHrd, nnd the grt'utest eon trusts
between polar Ilnd tropienl nil' mllsses will be exhibited during tht'
spring. The Pe nil' is still cold, and the lnnd lll'ellS in tempernte
latitudes are bei1lg h('nted, Hence when fresh Pc nil' comes in con­
tact with Tg air 'generous mins almost invnrillbly occur along the
frontal boundary, and in addition numerous instability showers
deyelop from stratocumulus elouds within the polnr ail'. in contrnst
to tbis situation, during the autumn when the sun begins to lenve the
polur regions, the polar front is being displuccd southwnrd, Then
both the polar mnsses and the Innd arens fire still fnirIy warm, find the
contrnst in the properties of polar and tropical nil' is 110t so gl'l'll t.
Rain is, therefore, less frequent.
The drought hazanl nt All1i1rillo and Dodge City difl'e'l's from thnt at
the four subhumid stations in that spring as well as win tel' stand::; ou t liS
!1 senson that may display long periods without precipitation.
Sum­
mer, on the other hUIld, has the shortest minll'ss inten'nls, Amtlrillo
and Dodge C'ity e~llericnce their greatest storm frequelleips and
maximum precipitation in summer. BcciHlseof tlIP frequentinnlsiolls
of Tg ail' during this season, muny cOllyeeti"e storms urc developpd ill
this air muss by the estahlislunent of steep temp('j'!lture lnpsl' rlltps
and through orographic lifting.
The question might bt' raised as to why the spring drought minimulll
vanishes ni Amarillo and Dodge Cit~T when compnrt'd with D,lllns,
Oklahoma ('ity, und Wichita. This cnn probably be explained by the
fact thnt in the southern High Plains region the polnr front frequently
tends to dPcelernte und to recede northward as a wnrm front. This
sequence of conditions genernlly operates at all seasons but is especinll~'
pronounced in the' spring when the P01l11' front is being displac{'(l
northward. The preyailing nil' mass that occupies the WlIl'm sector
':J Thi~ ('an be llxplainpd by rrL~fluellt snow tlurril's or minor }tlllUUIII.S of pn'dpllUlion frolll stratc){'llrnolu..:.
clouds that. charncteri'lticall:; interrupt periods without precipitation in this area in winter.
~
H:-­
~
t:::
o
~
....~
~
bl
AMARILLO, lEX
j-
1--1+1--1-1-+ j-.- ]J
j-­
~
~
.....
~
C'>
<r.>
.JO
~
~
t:l
t:::
DODGE CITY, KAN5. ~~1~~•__
!~~j4-~H7~1~_~
>.
'" o//l/
7.
. . . - •. ­
~/.~, ~~~
$~- ~.~ti;:..,.~h-;f§:,
:.; .'~
~K401.~· 1;:2
~,~ .,.., ./, ••. ".
!1~~:s /;
~"'&~~"
:·,r~t
:;. ~ j:x
.~~ ~ ~~
A7J~, 7.
':':{,-rt:-
V>"m;
II
~
M
~
J
J
0
A
•
R-
o
00·03
PRECIPfTATlON
....
.oa'il
'2"1~
t
'"
,.
16·1,
2'0-23
_
t:;
t"'
~
E:l
.2""UII
FIGUHE 14.-A verage diurnal distributiOIl of rainfllll by months at the nine stations indicated.
stlltion are shown in table 1.
o
C1
ththH)
/.>;..j ~ f§R]j ~:TI .~
.()4-07
I
§....
The exact years covered for each
i~AIXFALL CHARACT.bRISTICS AS UELATEn TO SOIL EUO::\roX
25
in this region is NPp air. When thL. air mass descends into the
Colorndo and New Mexico piedmont from the Rocky Mountnins, it is
relatively dry and is gaining moisture by evap0l'l1tion from the land.
There is, therefore, a less fnvornble opportunity for precipitation and
a consequent greater drought hazard.
DIURNAL VARIATIONS IN RAINFALL AMOUNTS
In order to obtnin a complete pict\ll'e of rainfall distribution it is
necessary to consider not only the sensollnl but also the dillrnal
vnriati011s. Precipitation amo\~nts for all of the stations were, there­
fore, tabulated by clOCK hours and by months in order to deternline
whether the diurnnl distribution varied from senson to seaSOll. The
raw diltn thus obtllined were smoothed both from hour to hour nnd
from month to month by using a weight.ed moving average of the
form
a+~b±(',
where b is the figure thllt is heing ndjusted nnrl a and
c nre IIdjncent unmodified amounts (table 11). The I·esults are
e)..-pressecl grnphicllily in figure 14.
For the enstern IIrea, represented by \Ynshington, Lynchbmg, nnd
Elkins, the lnte spring nnc! summer months show n distinct concen­
tration of rninfallamounts in the lute afternoon (fig. 14). Autumn,
winter, nlld early spring vnrilltions are not sufficiently pronounced to
permit of generalizations. The afternoon maxima during the months
of April through August are generally associated with convcrtiye
instability resulting from the maximum diu mal temperlltures of the
middle ilnd late afternoon. The filirlv even diunlill distribution of
rainfnll ilmounts during the remainder" of the yf'ur is due to the fact
that preripitation during the autumn, winter, nud early spring is
principally of cyclonie origin. Since no marked conrentration of
frontal passages or frontal activity is to he expected, this lnck of
diurnal variations is not surprising.
Dallas and Fort Worth (fig. 14) rereive most of thGir late spring
i1lld early summer (April-Jmw) precipitation during the night, when
radiation from the tops of the. cumulus and cumulo-nimbus clouds
that have deyeloped during the day and from other moist In.yers aloft
causes cooling and produces vertirul movements, with a('companying
precipitation. While nighttime eonvertive precipitation through
radiationnl ('ooling is not limited to the Plains and prairie region, it
is especinlly effe('tive there because of the ,Particular moisture and
temperature structure of the air aloft durlIlg t.hc summer season.
Hence, romplete explanation of the high nighttime rainfall amount.s
must await a detailed investigation of the na.ture and origin of the
moisture and temperature structure whirh prevails during this
period. During lttte summer, ho\\,eyer, moderately prononnced
afternoon maxima and night minimll lire displayed. For the other
months the l'flinfallnmounts nre well distributed diurnally.
Tlw foul' remnining stutions-~~Okluh()ma City, Wichita, Amnrillo,
and Dodge City- all lie well within tIl(' ilrea shown by Kinecr to have
a nighttime preripitatioTl mn.ximum in SUll1mel· (4).
This diurnal regime is displayed dlll'ing the months of May through
September (fig. 14), the merhanism beillg essentially the same as
that producing nighttime precipitation at Dallas and Fort Worth.
A slight incrense in the contribution of late afternoon cOIweetive
showers to the monthly pl"cripitation is noti('enhle in .Tllly and August.
26
TECI:t:XICAL BULLBTIN 698, U. S. DEPT.
O}'
AGRICULTUUE
REGIONAL RAINFALL CHARACTERISTICS AND THEIR RELATION TO
SOIL EROSION
VIR(,INIA.WEST VIRGINIA ."REA
As l'egnrds rainfall charuetel'istics Imd the corresponding nature of
the erosion hazards, the Virginin-'Yest Virginia nrea, llltty be divided
into the coastal-Piedmont section and the western mountainous
section. In the coastal-Piedmont section the dunger of erosion
through sheet wash and gully cutting is greatest. during the swnrn(,T
und early autumn months, when storm frequencIes, storm amounts,
and precipitation intensities are at a maximum. During spring nud
late llutullm, and pnrticulnrly in the winter, rninfnlls are of long
duration nnd intensities llre low. The greatest nll1011nt of Ulass
movement, therefore, occurs n,t this time of the yeur (3).
In the western pnrt of the tHen totnl Tuinfull is higher than in the
eastern beeause the altitude in the mountainous seetion is sufficiently
great to induce preeipitation from eonditionnlly unstnble nil' llHlss'as
and, in some illstnnces, to produce true orogl'llphie precipitation. The
storm frequency is, therefore, higher in this section nlthough the uctual
storm amounts of ruillfall nre npproxinmtely the i"ame as on the Pied­
mont and Plains. Since the ma)':i.lllum intensity effect does not curry
over into the autumn, sheet wush and gullying are apt to occur ulmost
exclusively in the summer months.
Nowhere in the Yirginin-",Yest Virginia nrea is the drought hazard
sufficiently great to be ('ritical. Twenty-five or more consecutive
days without rain are to be expected ttppro)':imately once every 10
years at Washington, and 20 or lllore such days lllay occur at Elkins
once in a decade; but since these figures mainly reflect autumn con­
ditions, the erosion risk is minimized. Spring and summer, which
are the seasons of principal importance in relation to crop production,
have 10-year drought e~-pectancies of only 12 to 15 days, the value
decreasing inland from the coast.
In the area as a whole, the flood hazard, with respect to large water­
sheds, is greatest in the spring. Several conditions combine to make
this season the one of maximum flood danger: Over 10 percent of the
spring precipitatioll occurs in rains lasting more than 24 hours;
intensities may be very high locally because of the rapid succession
of warm- nnd cold-front precipitation; and snow melt ma.y contribute
appreciably to the stream flow.
On small watersheds, however, floods are apt to O(,('.UI' with the
greatest frequency during the summer, when thundershowers are
most frequent. Since the rainfall i1Jtensity may be as high tlS 1 inch
in 15 minutes, whenever these storms hn,ppen to be centered directly
oyer tt smttH drainnge basin local floods will result, and a great amount
of soil erosion will ensue.
SOUTH.CENTRAI. PRAIRIE REGION
"\Vherens summer nnt! enrlv autumn !tl"e critil'al sensons in the
Virginia area, in the prairie region of Texas, Oklahomn, and Kansas
the most serious erosional damage is apt to be produced in the spring
and early summer months. During these months precipitation
nAIN~'ALL CHARACTERISTICS AS RELATED TO SOIL EHOSlON
27
intensities are at a maximum and storm amouuts of rainfall are high.
Again, as in the east, ,..· inter rains occur mainly in storms of long dura­
tion and low intensity. The danger of erosion through sheet wash
and gullying is therefore at; a minimum at this time. The winter
ruins may occasionally cause floods on large watersheds, but the
hazard is not nearly so gl:eat ns in the eastern area since winter storm
frequencies and amounts are both yery low.
A.lthough rainfall intensities are not so high as ill the Virgil1ia­
'West Virginin area, the factor of climatic risk so strongly influences
soil erosion that the erosion hazard is, in many respects, as great.
At Dallas, which in this respect mn,y be taken as representative of the
area as n whole, a rninless period equaling or exceeding 24 days oecms
on the average once every year, nnd 30-day intervnls without precipi­
tation may be expeeted 3 }Tears in 10.
The fact that. the drought incidence is high during the sUlllmer is
particularly significltnt. Such a drought may be terminated b.Y
intense convective precipitation. which mil,}, carry ItWl1Y an abnormally
great amount of tht. finely pulverized sUI'face soil. There is e,-ery
reason to belie,·e. therefore, that the less intense smnmer rains of this
area cause as much soil wastnge in many instanees us the more intense
fulls that oecur during the summer in Virginia. Another significant,
efl'eet of the long periods without. precipitat.ion is related to tIl(' high
wind velocities which characterize this region. Baring of the soil
t.hrough drought-induced crop failure frequent.ly exposes a great deal
of land to the direct action of the wind.
SOUTHERN GREAT PLAINS REGION
The high drought incidence as an index of climatic risk is of pre­
eminent significance in any considemtion of erosion on the southern
Great Plains. High wind velocities occurring during the winter and
spring (9, p. 239), when pressure gradients are steepest and drought
hazard is greatest, accotmt for most of the soil wastage that haR
occurred in this region. Where man through farming or overgrazing
has destroyed the original short-grass vegetation, the occurrence of
rainless periods of long duration has resulted in the exposure of the
grotmd surface and the ,"vind has beon enabled to work with maximum
efficiency in removing the surface soil.
The significant point is not. that storm frequencies and amounts Ilre
normally low in this aren, but rather that even minor fluctuations in
minfall amounts nre sufficient to cause crop failure or to ta,x over­
grazed land to such an extent, that subclimax t,ypes of vegetation.
unable to prevent. excessive run-off. are enabled to displaee tht' normal
yegetatioll. 1Vhere intense SUlluner showers follow sueh n spring
drought the soil is particularly subject to removal. and t.his hn.zard
is ndded to tht1t of removal through blowing.
Inasmuch as rainfall intensities are reln.tively low and slopes are
gentle, the flood httzard is not normally ncute. This hazard hilS,
nevertheless, been greatly incrensed through the removal of the
natural vegetal cover. For general flood conditions the spring and
autumn seasons are most critical because of the frequency of both
,..i despread and intense storms; wherons the spring and summer
seasons yield most of t,he situations in which flash floods are produced.
28
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
EXTENSION OF THE PRESENT MODE OF INQUIRY TO INCLUDE OTHER AREAS This study, while complete in itself, seems to indicate the feasibility
of and the need for extending this type of investigation to include other
areas. Although it has not been the intent to demonstrate a metho­
dology, such a demonstration has been a necessnry byproduct. of the
inquiry nnd it might therefore be useful to summnrize the geneml
npplicnbility of the techniquesnud appronches employed.
The nnnlysis of rai1.lfnIl records in an npproximately homogeneous
region makes it possible to determine those minfnll chnracterrstics
that are significnntly related to the soil-erosion problems of the nreit.
While the determination of sensonal variations in rainfall intellsities,
storm frequencies, storm durntions, and storm amolmts of rainfall
from individual station records in no wav constitutes a substitute for
Ill'eal studies based on datu. collected n£ a close network of gages, it
nevertheless supplies indispensable information. Rainfall intensity
is directly related to rate of run-of!' and hence to sheet, wash and gully­
ing. Storm durat·ion is important, pnrticularly in its benring onflond
hazard. Storm freq uancy. tts an index of drought, hazard nnd ns
relnted to the soil-moisture deficit., is likewise n. very reu.l lwd basic
factor in soil conservation problems. Storm nlllolmts of rainfall are
critical because the storm amounts and characteristics largely deter­
mine the degree and nature of the erosion produced by mechnnisms
involving water.
Analyses in these terms nre, tllerefore, both useful and necessnry.
They nre also practicable, since many datn. are already collected and
awnit Illlalysis. If studies of tlus natW"e are pursued it should be
possible to test nnel elaborate certnin relationships demonstrated in
this study regarding seasonal variations in rainfall characteristics, the
correlation between I5-minute intensities nnd storm nnlOlmts of rain­
fall, nnd varia.tion from aren. to area of the diu11lal distribution of pre­
cipitation.
This type of study also permits a more accurate q uantitntive inter­
pretntion of the effective meteorolo~i('al forces that. determine the
climate of a region. An understlllldmg of the physical fnct.ors that.
cnuse rainfall is of especial significnnce in that it. affords n logicnl bnsis
for extrapolat.ing the m.:isting climat.ic records to ext.reme meteorologi­
cal condit.ions.
The three indicated approaches to the problem of the relationslup
bet.ween precipitat.ion and soil erosion should be developed simultnn­
eously. This pa.rticular study emphasizes one of these approaches­
the analysis of indiyidunl st.ation records. If t.his approach is com­
bined wIt.h areal studies, which will yield information on rainstorm
morphology, and meteorological studies, which will synt.hesize the
descriptive material and pernut t.he making of sound generalizat.ions,
soil conservation and flood problems will be greatly clarified. Cer­
tainly, if all these lines of approach are oriented in such a manner that
t,hey are complement.ary Plllts of one general method, a definitive solu­
tion of the question of j liSt. how precipitation and erosion are related
will be supplied.
RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION
29
LITERATURE CITED
(1) BAILEY, .REED W., and CONNAUGHTON, CHARLES A.
1936. THE WESTERN RANGE IN WATERSHED PROTECTION. In The Western
Range. 74th Cong., 2d sess., S. Doc. 199: 303-339, Ulus.
(2) HOUK, Iv_w E.
1921. RAINFALL AND RUNOFF IN THE MIAMI VALLEY. Miami Conservancy
District Tech. Repts., pt. 8, 234 pp., illus. Dayton, Ohio.
(3) IRELAND, H. A., SHARPE, C. F. S., and EARGLE, D. H.
1938. PIUNCIPLES OF GULLY EROSION IN THE PIEDMONT OF SOUTH CARO­
LINA. U. S. Dept. Agr. Tech. Bull. 633, 142 pp., illus.
(4) KINCER, JOSEPH BURTON.
1916. DAYTIME AND NIGHTTIME PRECIPITATION .-\.."<D THEIR ECONOMIC
SIGNIFICANCE. U. S. Monthly Wp.ather Rev. 44: 628-633, illus.
(5) McDoNALD, ANGUS.
1938. EROSION AND Irs CONTROL IN OKLAHOMA TERRITORY. U. S. Dept.
Agr. Misc. Pub. 301, 48 pp., illus.
(6) MUMI CONSERVANCY DISTRICT, ENGINEERING STAFF.
1936. STORlkl RAINFALL OF EASTERN UNITED STATES. Rev. ed., 352 pp.,
illus. Dayton, Ohio (Tech. Repts., pt. 5).
.
(7) NEAL, J. H. 1938. EFFECT OF DEGREE OF SLOPE AND RAINFALL CHARACTERISTICS ON
RUNOFF AND SOIL EROSION. Agr. Engin. 19: 213-217, illus.
(8) THORNTHWAITE, C. \V.-umEN.
1931. THE CLIMATES OF NORTH AMERICA ACCORDING TO A NEW CLASSIFICA­
TION. Geogr. Rev. 21: 633-655, illus.
(9)
1936. THE GREAT PLAINS. In Goodrich, Carter; Allin, Bushrod W.;
Thornthwaite, C. Wanen; and others, Migration and Economic
Opportunity, the Report of the Study of Population Redistribu­
tion, pp. 202-250, illus. Philadelphia and London.
(10)
1937. THE LIFE HISTORY OF RAINSTORMS. PROGRESS REPORT FROM THE
OKLAHOMA CLillATIC RESEARCH CENTER. Geogr. Rev. 27: 92-] 11,
illus.
(ll)
1937. THE RELIABILITY OF RAINFALL INTENSITY-FREQUENCY DETERMINA­
TIONS. Nat!. Research Council, Amer. Geophys. Union Trans.
2: 476-484, iUus.
(12) YARNELL, DAVID L.
1935. RAINF_-l.LL INTENSITY-FREQUENCY DATA. U. S. Dept. Agr. Misc.
Pub. 204, 68 pp., illus.
APPENDIX
TABLE 2.-Seasonal and annual mean storm frequencies for the periods indicated
l
I
!
Station and period covered
, Spring
Washington,Va.,
D. C.,
1905-35.-------------------------1
LYnchburg,
1902-33_.
____ .______________________
Elkins, W. V8., 1905-35___________________________ ._ I
Dallas, Te.'t., 1914-35.________________________________
Fort Worth. Tex.. 1899-l931>-­ _______________ . ____ .__
Oklahoma City, Okla., 1900-1935____________________
Wichita, Kans., 1903-35 _________________________ .___
Amarillo, Tex., 1903-35______ ._______________________
Dodge City, Kans., 1894-1935________________________
38
36 'I
54
28
24
:ti
29
22
22
Summer
I~i
'
~..:~~
j
WInter
43
43
58
21
19
23
26 ;i
26
39 I
136
134
195
29
:ti
21
29
29
44
22
16
12
10
89
28
1810
15
12
77
i7
21
18
19
\)2
77
81
30
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
TABLE
a.-Storm amounts of rainfall by seasons expres8ed as percentage of seasonal
rainfall amounts at the nine stations indicated
I
Station,
period, and
Sum· ."'U· Win·
(hundredths of an Spring mer tumn ter
Inch)
amount of rainfall
Washington,
D.
C.,' Per.
1005-35:
1-10__________ .......
11-20.____ •• __ .......
21-50....__........__
51-100. __ .....__.....
OverlOO............
Lynchburg, Va., 1002-33:
1-\0••
11-20... .............
21-50...............
51-100..............
O,'cc 100... ........
Elkins, "'. Va.,1905-35:
l-lO_-. __ ~ __ .. __ • ___ .. _
11-20................
21-50.......... ......
51-100............. ,.
O\·erl00............
Dallas, T6., 1914-35:
1-10.................
cent
Per.
cent
48.9
14.9
2O.S
Il.O
4.4
48.1
49.0
11.9
Ii. 1
15.0
7.0
52.0
H.4
18.3
9.8
5.5
52.0
H.5
16.8
9.6
i.l
45.3
H. j
21.0
12. j
6.3
52~6
-17. 8
17.6
21.0
9.8
3.5
48. 6
16.1
20.7
9.1
5.5
12.9
20.9
8.6
5.0
15.2
23.3
9.4
4.3
43.8
47.8
52.7
50.2
10.9
8.3
9.1
12.3
12..2
7.7
"",S 45.0
11.4 13.8
IS.8 14. 3
13.1 15. 9
11.9 Ill. 0
47.1
12.0
14.9
12.0
14.0
44.5
14.7
20.3
11.8
8.i
0" . . . . . . . . . . . . .
~t~L:::·:::::::::·
51-100..............
O\"erl00............
Fort 'Vorth, T6"
1899-1935:
1-10._..............
11-20..... ",,,,.,,,,
21-50................
51-100...............
O\"erl00...........
TABLE
50. ..
13.1
18.1
10.7
7.4
~~:~ 1~:~
g:g
12.0
13.4
period, and
i
sum'l Au· Win·
(hundredths of an Spring mer tumn ter
Inch)
amount of rainfall
I '
i~i~II'
Oklahoma City, Okla.,'
cent· cent
1900-1935:
50. 6
13.5
16.3
11.2
8.4
51. 1
13.1
19.3
10.2
8.3
!
I
I
Station,
Per.
cent
1-10••.__••••••_.....
11-20.•____._.•.. __ •.
21-.';(L.____ •• ,......
51-100.... ...........
O"er 100............
Wichita, Kans., 1903-35:
1-10............ __ • __
11-20....... __ .......
21-iIO................
~;~1.00==~=:=== •• =.=
c~
45. 1
12.2
:lO.1
U.3
11.3
,;i.5
12.9
15.8
8.5
5.3
M.5
12. I
63.4
12.6
11.9
7.0
45.0
H.8,
20.8
10.6
8.8
52.6
47.5
16.3
15.9
10.3
4.9
61.2
12.3
15.8
i.4
3.3
49.9
14.2
Ii. 0
. . . . . . . . •••
AmariUo, Tex., 1903-35:
1-10.. ___ ...___ ~ __... ___...
11-20................
21-50................
5HOO...............
O\"erl00............
Dodge City, Kans.,
1894-1935:
~:~
1-;;'1,-;;1-;:;
cent cent cenl
44.5
15.0
17.7
12.3
10.5
49.3
11. 9
17.5
11.6
9.7
ii=[Io::::::::::::::::
21-50.............. ..
51-100.............. .
Over 100.......... ..
15.0
10.1
8.3
14. I
6.6 3.3
13.6
19.6
12..8
d.5
52. 7
12..3
16. 5
13.0
5.5
59.9 13.9 20.9 5.1 1" 50.3
13.6
16.2
M.O
! 16.6
68.9
12.4
13.1
4.9
l~J
13.3
t 19J
4.-Number oj storms producing measurable precipitation
I
I
~I.-\Ug,
i
Station. period, and year)I Jan. :i Feb. Mar.; Apr. r May [ June
Washington, D. C., 1905- i
35:1905__..................
1906...................
1';
9 '
}~L::::::=:::::::::
,
1~
.
8
7
1~
g
Il11 Ii
12
1909.............._.._.
1910_........._........
1911...................
1912...................
1913...................
1914_.... ___ ...........
1915.........._........
1916__• __ ..............
191;..... ..............
1918..__ ...............
1919....._.............
1920...................
1921...................
1922...................
1923...................
192~.......__..__ • __•..
1925......._...... __.__
1926.__......... __.____
1927..__...............
1928....... ____........
1929___.... ______ ......
1930.__ ..._............
1931...................
1932.__...............,
1933........... _.•••___
1934........_...._.....
1935.._____ ._.......__ •
S
13,
9
S
19
6
U
14
10
13
7
10 I
11 I,
8'
13,
6!
15;
10'
13
9
9!
13,
4
10
S'
9J
,
i!
12
11
18
15
19:
Me.m............. ,./
10'
9:
12
j
11
12
9
8
8
8
8
109
I!
'
12 I18,
10: H ~
10
13
!
I
I
5
14
15
12
9
3 I
14'
19 ,
9110'
9
9 'I
1I
10
14 1
12,
6
11 I
121
S
10
10
8 I
9 I
10 I
12
9"
i
12
11,
17'
12
10
Il
7
11
7
l~
I
f
I
nf
13!
2"2
8
14
14,
I
19
26
I
14
11 i s .
8, 15 t
11
Ii
16
1
I
12
9,
19
17
9
8
10
!O
12 f
17
10
12!
5
9
U'
10'
15
17
14.
9
16
15
11
22
11
7
13
17
18,
13
14
12
25
16 '
15
12
14:
15
i,.
I
I
j
13
11
7
1
1
j• 15
190 I
13
14
19
13
14
15
9 1
15
12
14
12
16
12
24
20
15
9
10
11
12
13 I
~30
22
17
I~' 115~:
19
23
20
15
~~
i
I
i
26
I I I'N0"'l
Ii
n!
H,
15
23!
11
10 '.
13
I
13 1
12'
17;
16' W!
1236 r
10 ','
1(\'
8
14
19 I 13!
15
22
13 I 131
19 'I 16
12
13
12
10
17
14
17
Jj
S
19
15
9
9
7
I
I
91 176!
Ii
I
14
i
I,
8
9
:'
1
11,
8,
4 I
10
14
8
4
9
8
Ig
6
10
12
6
12
7 I,
:I f
i 6 1I
Ig
I
S
9,
7I
10
-I
,8
10
;
4
,
6 I
I
I
10:
13
5
11 f
5,
,9
9
S
8
9
13
3
17
13
13
14
9
10
13
5
10
7
16
19
10
.
6'
19
14
9
~ I
~',
3 t
14!
11 1
9 I
51
9
8
8
11
13 I
i I 14,
16 i l l S
14,
! Dec.
Sept. j Oct.
i
14"
10;
13 ~
4
11
5
8
10
7
7 j'
I1
1~
5
5
9.
7
5,
7:
1_ ,
5 I,
8'
S
8;
8,
15!
12!
7
15 I~
S
7
10 12 6
12 8
11
8
10 10 5
1,3 9
12 9
11 11 14 3
12 6
13 10 15 10 l~ 10 31
RAIN1'ALL CHARACTERISTICS AS RELATED TO SOIL EROSION
TABLE
4.-N'umber of storms producing measurable precipitation-Continued
Station, peri:d,
and,)y.e~
Jan. Feb. MIU'. Apr. May
Lynchburg, \ a., 190*-33.
190L............. ___ • --.. -- •• ',.'
9
1~(
1903.........__ ...... _.
11
1904_________ ... __ ._..
11
7
1905__ ._ ............ __ •
1906.__ •••____ •• ____ '"
11
S
l00i...... _. __ ...... ,
8
5
6
10
1908........__ .........
191J1l...__ ....... _.... __
9
16
11
12
1910_____ .. _•. _. __ " '"
191L___ .... _.•••• _ •• '_
11
9
S
11
1912_____ • __ ._. __ ••. _.
1913___ ... ___ ••••••• _.,
13
11
191L.... _...... __ ••• _
Ii
13
1915_.. __ , ____ .. ___ "..
17
7
1916__________ .... _...
II
9
191L_____ ....... __ • __
13
8
11
6
1918..__ .... ___ ........
1919____• _____ .... __ • •
5
7
1920______ ••• ___ . __ ".
12
12
192L...___ • _____ ••••. _
5
10
1922.___... ________ .. __
11
17
i~~t=:::=::~::::::':
1~
l!1"~ _______ ......
_.. __ .
1926_________ .. __ ._____
1927.... __• ___________ •
1928,_ .. _____ •• __ • ____ •
l=::::::::::=:~::::::
193L______ .. _.. __ ... ______
1932..__ .. __.. ____..___
1933.. ___ • ________ .____
Mean.________ --____
Elkins, W. Va., 1905-35:
,
190L, ........... __ .. _
1906",,, .. _______ ..
m~:-:::::::::::::::::
1913___________________
1914.__________________
1915.__________________
1916__________________
1917_________________ _
1918___________________
1919__________ .________
1920___________________
1921.__________________
1922_________________ ._
1923__..__________ ,,___
1924___________________
1~~ __________ .________
1926________________ "'_
192L_________________
1928______ • ______ ._____
1929__________ .________
1930__________________ •
1931.._____• ___ •• ____ ,.
1932._____..... ____ .___
1933__________ •. _______
1934...... ,
1935____ . ____ '
Mean_____ ..... _
11
12
14
16
11
11
4
12
15
12
12
4
8
15
15
9
9
9
17
~
1~
9
11
9
5
6
11
12
7
g;
6,
1~
1~
11,
10
10,
6
12
,
14
14
12
14
18
13
6
9
6
12
8
15
12
11
15
11
g9
11
11
6
8
10 !-10
11
12
13
15
14
9
15
18
:!'2
9
21
8
13
Ig
t~ 1
I
IS
19.
191
15
16
18
9 f'
21
17
15
22
10
13
12
15
11
23
12
10
20
15
18
15
10
t~
g
U
12
Ii
13
13
15
14
20
16
16
11
17
I
14
15
19
21
13
12
16
18
22
14
16
13
18
10,' 14
17
15
21 /16
14
16
12
18
14
13
JO
20
9
13
16
28
8
19
14
18
,
81
20 i
14!
20
28
18
13
10
20
19
6
13
9
14
17
11
13
10
21
11
12
14 I
18!
S
II
17
10
Ii
9
11
15
3
12
11
12
10
21
11
15
12
17
18
13
\9
15
27
12
15
Ii
8
8
19
19
7
17
14
S
20
9
II
13
22
27
14
17
9
13
10
10
7
14
14
18
20
18
21
18
12
14
~?
~
~~ I l~
15
7
15
12
9
20
9
14
12
6
16
il::::...:::::::::::::
ii11
1909__,, _______ .. ______
1910__________ .________
'''is' '--iii' '''-g--'23'
9
8
9
7 i
1
(June'~:;;- Aug'jsept.! oct., Nov••Dec.
14
13
13
13
19
1~
g
16
1~
I
18
13
1
10
I~
'
Ii'
5
7
12
16
13
4
9
9
10
13
10
3
12
10
Ii
4
5
1
6
12
5
7
6
8
13
5
13
10
S
5
9
,
12
1
6
9
l~
~
14
12
8
12
11
l~
19
16
18
20
19
27
l~
;12
25,
19 I
17
20
21
9
8
23
~
Tl9
16
18
21
21
12
26
12
26
20
12
10
19
17
16
17
17
24
20
13
15
22 j
19
19
I
:g
~~
'!2
9
24
~'2
23
15
23
10
19
20
12
28
\0
15
19
23
22
16
23
20
18
20
20!
18 I
17
20
24
38
16
11
19
16
, 14
,13
2i'
14
13
21
19
35
20
2167
!
35
8
21
I
If
1~
18
21
~
5
196
14
i~
I~'
1~
14
35
15
8
3
7
II
7
13
11
8,
87 i
1
22
8
14
15
10
6
13
21
19
10
6
16
10
9
6
11
9
10
12
i
20
2"2
10
6,
11
6 ·--· .. 1----,·
I
7
5
5
9
7
13
3
7
6
12
7
7
7
4
9
18
18
22
13
12
i
II
15
14
6
16
10
8
-----­ ...
I
I
I
~~ i t~
~
22
14
?8
12
24
~1
12
20
26
15
16
Ii
Ii
20
19
24
17
21
19
2'2
19
24
25
20
11
20
20
14
12
:!'2!
23
29
7
14
12
13
13
5
13
Ii
18
21
11
13
24 I
18
21
8,
10 I'
20
13
12 I
IS \
21
I
28
i
14
17
14
25
6
8
14
9
19
s1'
17
Ig
h
10
11
5
11
12
10
7
8
--t-......
'.
s;
9
I ' !
9
15
4
8
8
12
5
13
9
10
6
10
10
7
8
14
12
14
1~
1
12
10
1~
I
I
1~!
,
~
I
8
12 1
7
15: 12/
10
13
t~
14'
7
16
12
12
,
16
11
16
12
14
I
14
12
15
19
13
14
18 1
15
g
13
11
13
23
7
18
11
5
3
21
21
12
14 (
!n
14
17.
9 i
I
14 1
11,
15 f
15,
14!
14 I'
11
8
16
12
14
l~
10
20
16
12
9
14
15
15
18
16
14
21
\0
18
18
8
15
13
19
13
18
13
19
151417-lsf19r:iOl2iJ('lS;14:12l3j15
32
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
TABLE
station, period, Bnd
hourly amount of pre­
cipitation (hundredths
of an inch)
5.-Frequency distribution of hourly predpitation
I
Feb. Mar. _",pro May June July Aug. Sept. Oct. Nov. Dec.
Jan.
j
Washlngton,D. C., 1905- '
35L_____________________
\----.-------------------­
610
360!
216;
207
155
104 I
2______________________
3______________________
4______________________
5______________________
6_____________________ •
487
311
212
174
127
93
601
495
325
261
272
207
197
152
146
104
102, 95
L=:=====:=:::::::::::I
~61 iI 37;
~ t ~~;
9_.__________________ ••
50
10.. _________________ ._
11_____________________
12.... _________________
13
I
50 i
29 I
40
20
I
47;
22 I
22,'
29
45
38·
36'
19 i
:51
460
232
151
.101
98
52
370
186
136
95
64
42
33
36
.16
29
30
37
23
24
15
17
It
36
34
34
19
1~
310
141
87
83
50
44
404
189
114
95
65
54
454
226
132
101
G5
54
575
305
240
160
119
9&
i24 ~~29 ~~26 :~30 26~
~46
16
27
15
12
42
33
28
15
28
31
23
17
j~:~~--:--::-~----i a: f: ~ ~ ~ 1:1 111:1
I·
~:::::::=====::=:=::::'
21-30__________________ '
Ig.
42,
~
13
~ijg::::::::::::::::::'
__ ~.i ____ ~_
5HIO__________________ l______ '______
1~ 46
19
321
1
1:
1~
22
18
22
18
24
25
16
19
28
23
27
16
g 36!
33
:1,
U! 53Po
i3!
42
60
57
2
1
15
10
~
17
~
17
~7
7
10
~6
1
3
~
382
203
120
97
64
67
~ t! ~
g 2218
ill~ ~ 1~
Ur~~~~~~~~~~~~~~d~~=~~I~~~: ~::~~: ~~~;~~ _ _J__ J__ J_ t l -~. :::::: ______
61-70__________________ •______ 1______
~7
1~
333
139
101
60
52
53
3
Lyn~'l;b!~:-V8:;.1002-33-:I-----·l--~---!.-----:
1._____________ .. __ .. __ , 566
------------------1'
I
522
481
-----1------ -----------1
293
3il
.•----- 489
395, 374
365
312
344
265
.234
244
228
184
J6.1, 183 I 158
131
143
114
J09
8.1
123, 62
89: 85
74 I 58
65: 65
47
52
61! 65
38
37
45
33
lL_________ ._________ 49 32 50 26
11 ..__________________
23
17
34
25
li____________________
22
29.
29
17
13_____________________
20
16
19.
17
10
14..___________________
19
32;
15
14
15..___________________
11
27: 15
1~ .. ------------------­
9
119
12
12
9
11..___________________
10
10
18..____ ._____________
11
6
10
8
19..___________________
6
8
8
6
20.. ___________________
6
3
9
7
46
21-30__________________
33
26
43
14
3J-40__________________
7
10
2
41-50_________________
2
1.
1
8
51-60____________________ .. __
1 I
1
2
2____
_____________ .______
3..
4.. ____________ -------­
5 .. ------------------­
6. __________________ .__
7.. ____________________ 1
8..-----------------­__ 1
9 __________ ._________
I
1
216
131 Ii 162
119
107 '1' 107
73
55
6.1 I 53
5J! 48
54
50
22 I 31
30 I 27
22' 25
20
16
17
14
15
19
15
16
5
15
7
10
7
11
6
3
oS
8
39
58
40
24
11
20
5
7
1
1
347
2
2
2
1
1 __ __
------'1--·--·
-----­
400.
412
539
lSI
188
189
149
98
112!I 136
99
124
114 I' 334
243
62
~ I 75
1l~ J
~
60
8_: 71
6,. 72
13,
44
44: 51
51! 55
109
41
36 I 29
60
42
82
24:
19
29
42 I 45,
53
19 i 35:
30
45
33 r
43
28·
36
23;
48
HI
IS l 21
27·
28·.
40
21
26 1 20 I 33; 16'
23
9
21:
15 I 21! 10
29
10, 13' 1O! 13 j 16
19
9 I
13 j
13'
24.
13
11
105
21:
11
14
:
9
7
14 f.12
10
10
14
6
11 i
9
9
8
11
11
8 i
4
9
5
11
8
12 '
5
!l
5
9
52
57·
47
48
35 I
27
30
35 i 20
20
12 I
2
21
20 !
8
.16:
1
1 ____ ..
17
12 I
5
7 1
93\
i
i
171
291
I
51
:!~i~~~~~~~~~~~~~~d~~~)::::~:i:;/
---: --·:·i
-!-____ J__ .__ --.--I l!' iIt:J!-:~::::~:;~;:~~~~~~
m~}~~~~~~~~~~~~~~~j~~_j~~~~~t~~~~ :~~~:~ ~~~~~~l----~-E=~= __ Jl-:~: ~~~~~~ ~~~~~~ ~~~~~~ 101-110________________ ,_____
1
1
7 - _____
2 ------ ------ -----­
33
RAINl!'ALL CHARACTERISTICS AS RELATED TO SOIL EROSION
TABLE
5.-Frequency distribution of hourly precipitation-Continued
s tation,
I
I
period,
and
hourly amount of pre·
cipitation (hundredths
of an Inch)
..
I
I
May June July Aug. Sept. Oct. No,'. De c.
Jan. Feb. Mar. Apr.
I
---------1·-- - - - - - - - - - - - - - - ------i-L
W~hf_TI!~~~~~~:'.._~:~~_ .......'.. ...........'......
1 .... " .........." .........
..1.... -..
Efr~~~~~~~~~!~~~~~~ ~~;~= ~~~~= ~~:=i~~~~~=I;..~!·I!::~:~:,: . 4:~·I':::= -':!' =:~: ~::~I'=~~~ ~ 2.._______..__..__.._..
3.______..........__...
4..... _______ .....____•
663
360
271
615
304
259
~:::::::=:::::::::::::: l~
f~
7...... __ ..............
630
341
221
478
312
233
349
243
164
255
179
140
227
208
156
142
104 I 116
m milM li~
119
48
8S
69
8, .., __...........____ •
97
58
93
76
9 .....................,
59
33
50
53
10.... __...._........__
61
28
70
54
11,....................
50! 27
40_,
46
12 ..._____.....__.. '...
31 I
8
33
3
13............__...__..
II
12
17
31
14...____ ............ __
30
4
16
25
15....._.._............
13
6
20
1197
16....__.._............
13
9
9
Ii ....__ .......... __...
12
10
12
18
18 ....................
6
8
13
10
19........_......... __.
4
4
5
5
20....__............... 1
2
136
12
392
21-30..................
21
39
15 1 9
31-40.................. 1
3 I'
8
41-50..................;
2
2
1
6
5HIO·.. • ..__......__.. ' .. ' .. I' ....... ,.,
2
74
j
56
57
52
33
30
3\l
21
35
29
14
20
11
13
72
18
15
4
I
I
~~
55
47
30
64
70
62
61
43
30
32
28
42
40
29
26
23
~
22
I,
22
21
11
15
13 i
6,
17
20 118
76
56
55
47
16
28
14
18 I
~
45
52
38
32
26
35
20
21
24
32
20
14
15
13
67
38
25
14
214
128
105
360
210
146
~~
~
445
208
184
4
I
I
1~ I
791
66 1
34'3 256
{:J6. i2
8
56
49
63 53
41
61 42
37
56 32
27
~_ 30
22
3
23
16 I
I3
24
11 i
23
16
10
7
14
6 '
14 17
7 i
6
4
10
6
8
2
3
9
11 I
2
47
22 i
7
13
4 I
4
3 I.. , ..... . 2 ........... . 47
48
I
44
37
23
36
13
14
13
11
13/
21
9
13
62
30
14
7
I
.,
!
!
miLm~~~I~If~II C~~·1.....
<::.1.....·
~;:;~~ ..... ......r; lll_!___!:::~:: ~~~ii~~:
.
II'
I.... .... ...... ......
111-120....................
2,
121-130 .........................
131-140... ' .............. " ........ ' ••.• __ ... ...... ......
151-160 .....__ .... ____ ..........__ I............ " ..'.
1
1 I .....• .................. i....·­
1 ! .................. _............ 2
1 ............ ,...... _•••_. 2 ..........., ..__........ ____ i~E~=:============== =====l===t==== =====f==== ====== ....~. ~~~~~~ ====== ~~== \====== =====
TABLE
6.-Frequency distribution of hourly precipitation
Station, period, and
hourly amount of Spring sum·I·<l.O. Win·
mer tumn ter
precipitation (hun.
dredths of an mch)
- - l! - - - -
Dallas, Tex., 1914-35:
I2._
...................
.. __ • __________
3.•. ,., .............
4.. , ' ...............
5................ : ..
6...................
7..... , .............
8...................
9... , ...............
10......._..........
11........_.........
12..................
13...........__.....
14..................
IS..................
16
17..................
18..___..........__.
19......_......._...
20........._........
21-30.....__...__._.
31-40._.............
41-50...............
51-100..............
~
~_
-----------------
552
239
159
126
108
100
66
80
66
39
39
34
32
26
20
31
29
26
16
12
122
65
33
105
!
318
128
~j
FortWorth, Tex•• 1~
934
1935:
394
1.........._........
2....___._.__...._..
276
3...................
167
146
4...................
5... __....__. __._.••
!II
6, ..................
66 f
61 !
7...................
8..............._...
60
9...................
47
25
10..................
11. __.....__......__
37
12........___....._.
28
34
13..................
14......__ ..........
33
22
15..................
16..................
18
17..................
13
18..........__ ......
18
19..................
13 20.._......_........
81
21-30........_......
20 31-40.........._....
0
41-50...............
51-100..........._._
20
I
555
251
137
lW 1i 120
62
111
43
87
41
55
43
55
30
44
26
47
26
41
24
32
21
26
23
24
16
26
20
25
13
16
16
20
10
13
15
16
69 I 81
46
24
57
Station, period, and
hourly amount of Spring Sum· .<l.u· Win·
precipitation (hun·
mer tumn ter
dredths of an Inch)
I
I
- - -- --' ..830
410
270
219
152
121
116
98
102
79
58
56
56
43
71
41
38
41
32
~I
405
231
138
106
100
66
70
62
50
48
36
43
38
30
36
32
25
28
16
25
109
..
~I
81
132 , 133
741 1.243 389
567 276
339 259 195
156
220
137 I 148
94
118
81
115 62 57
78 il
52 i2
61
4~ 43
39 42
43 43
46 j
27
23 27(
21 27
18 29
15 22
14
174
80
30 64
42
28
26
99
I
34
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
TABLE
6.-Frequency distribution of hourly precipitation-Contiuued
Station, (l<'riod. and
hourly amount of Spring Sum- Au- Wlnmer tumn ter
precipitation (bundredtbs oC !III !neb)
----
Oklahoma City. Okla.,
1900-1935:
1. __________________
2__________________
3___________________
4_____________ ._.___
5___________________
6___________________
7___________________
8__________________ •
9___ . _______________
10_______________ • _.
11. _____ •________ ._
12___ • ______________
13__ • ______________ •
14.________________ •
14L_________________
IIL _____________ . ___
17________________ •.
18__________________
19__________________
20__________________
21-30_______________
31-40__ • ____________
41-50 _______________
51-100______________
Wichita,
Kans.,1903-35:
L __________________
2___________________
3___________________
4___________________
5___________________
6___________________
7___________________
8___________________
9___________________
10 __________________
11__________________
12_________________ •
13. _________________
14__________________
15 __________________
16. _________________
17_____________ •____
18_____ • ____________
19 __________________
20__________________
21-30_______________
31-10.______________
41-50________ • ______
51-100. _____________
-- I
876
435
395
215
157
132
130
99
85
61
68
61
51
41
52
36
40
28
27
85
132
63
:13
82
8i3
366
282
177
188
114
\10
68
58
96
28
30
22
15
19
15
13
19
10
30
52
20
4
2
886
449
308
235
213
152
111
103
101
100
64
53
50
34
36
32
34
32
31
742
398
232
215
176
136
90
83
74
80
52
40
36
24
20
34
28
22
28
4o:l
210
124
71
S6
32
20
26
21
68
Jl
17
13
13
589
:132
216
145
134
93
68
82
74
88
64
67
f 51
39
37
28
29
t
30
I
,
27
019
149 l 163
74 i lJ6
29 II
49
79
136
I
1
..
-
!
]6
I
I
128
65
35
56
sum-/ tumn
Au- Win­
-.-. --­ ---
I
612
292
185
177
1:13
li5
93
,(2
127
98 I 99
104
69
81
59
72
50
54
45
43
50
31
47
56
26
40
19
41
23
18
35
83
51
182
125
75
77
56
44
125
95
985
4:13
3i3
264
202
178
126
Station, period, and
hourly amount of
precipitation (hun- Spring mer
dredths oC an ineb)
8
3
5
7
7
13
20
8
------
5
AmariJIo,Tex.,l!I03-35:
1. __________________
2.__________________
3___________________
4 ___________________
5___________________
~:::::::::::::::=::
576
:124
188
154
119
88
78
62
45
49
30
39
31
29
22
26
19
14
14
15
i3
44
15
:13
8____________ •• _____
9___________________
10__________________
11._________________
12__________________
13__________________
14 __________________
15•• ________________
16___ • _______ ._.____
17__________________
18_ •________________
19__________________
20__________________
21-30______________
31-10_______________
41-50 .• ____________ •
51-100 ______________
Dod~ City, Kans.,
18I. __________________
1935:
2. _____. ____________ 1,029
491
3___________________
264
4 __________________ •
237
5___________________
214
6___________________
128
7___________________
101
8___________________
80
9___________________
56
10__ • _______________
94
11 ..________________
50
12_________________
66
13. __ •______________
:13
14. _________________
35
15. _________________
49
16.• ________________
017..... _____________ 19
18 __________________
22
19 __________________ i
20______________ • ___
30
21-30_______________
98
31-10... ____________
37
41-50_______________
:13
51-100______________
35
_.
t~r
569
310
194
136
US
93
63
i1
flO
69
52
42
45
37
25
30
29
26
16
27
133
74
42
115
641
293
204
136
\13
82
663
390
257
202
156
126
100
80
83
80
51
43
49
31
46
42
23
24
21
31
150
i90
323
208
1i3
150
110
84
85
43
61
43
30
22
22
39
22
15
12
i
24
69
29
22
:13
S4
flO
154
271
172
110
62
64
45
29
21
12
24
12
6
3
72
47
39
43
34
24
34
28
21
22
19
16
20
19
75
32
16
31
6
7
3
4
3
0
3
7
4
3
2
504
200
104
65
54
43
19
25
10
15
4
4
2
1
1
3
0
1
0
I
7
I
3
I
I
35
RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION
T.ABLE
7,-Frequency distribution of maxim'um rainfall by is-minute intervals
Rainfall (hundredths
of nn inch)
--------1--- ------Washington, D, C ..
1901;-35:
4 and over__________
7 and over__________
10 and over_______
13 and o"er_________
16 and over_________
19 and o\'er________
22 and o"er_________
25 and over_________
28 and o\'er_________
31 and o"er_________
34 and over_________
37 and o"er_________
40 and over_________
43 and o\'~r_________
46 and o"er_________
49 and o\'er_____ ____
52 and o\'er.________
55 and over_____ ____
58 and over________
61 and over._______
403
255
187
143
110
87
64
47
39
32
26
18
15
9
8
7
4
2
2
592
468
392
343
298
259
234
206
183
168
155
138
123
108
96
83
i5
65
56
2
64 and o\'er_________
0
67 and over___• ________• __ _
70 and over________ _
i3 and o\'er___ •___________ _
76 and o,er___ .. ___________ .
i9 and o\'er___••____ •____ ._
82 and o\'cr.__•_____ •__ ._._
85 and over__••___________ _
88 and o\'er______________ _
94 and over___•___________ _
103 and over________ • ______
106 and over_______ • _____ _
109 and o\'er______________
112 and over____________
121 and over________ • _____ _
124 and o"er______________ _
12i and o\'er_____________ _
145 and o"er______________
H8and o\'er__ ..... ______ __
Lynchburg, Va., 100233;
4 and o\'er _________ ,
7 and o\'er__________
10 and o\'cr________
13 and over_________
16 and o\'cr_________
J9and o\'er________
22 and o'\"er________
25 and o\'er__.______
28 and o\'er__•_____ _
31 and o\'cr_.______
34 anci o\'ec________
37 and o\'er_________
40 and over_________
43 and o\'cr_________
46 and o\'er_________
49 and o\'er_______
52 and o,er__..______
55 and o\'er.________
58 and o\'cr--------61
64 and
and o\'er--------o\'er_________
~7an1 o\'er_________
'0 and over_________
i3 and o\"or_________
76 and o\"er_________
79 and over_________
453
281
100
144
167
59
31
133
112
96
84
77
67
19
13
56
2
22 ... ____ _
34
11
5
4
4
4
3
7
6
4
7
5
4
28
'Ii .. _____
25
29
26
23
16
13
11
9
39
8
55
49
335
229
16.,
122
97
78
64
48
38
31
24
18
10
8
i
3 ..__ __
2 ____ __
3
34
28
22
2
2
1
1
I
1
3
3
82 and o\"er____.____
2
85 and o\"cr••_______
1
91 and o,'er_________
0
94 and over______________ __
97 and over ______________ _
106 and o\'er______________ _
124 and o\'er._____________ _
12i and over. ______ • ___ , __ _
145 and over______• _____ __
163 and o'er_____________ _
S
7
5
4
3
!
mil
1
1
fl
1
4
0
4 .. __ ..
45
38
26
21
18
15
13
9
~! ~
\l
II
a
3
---.~
261
125
68
30
18
13
;
4
2
2
2
1
I
..
__ .._
_____
..__ ..
___ ..
____ __
.. __ __
____ __
_____ •
~.
1 -----.
1 ______
1 ____ __
1 _____
1 _____
~~~ i
416
II
.!
~1 ..________
--~- ======
..__
Elkins, W, Va.. 1001;­
35:
700 1,014
4 and ovcr__________
4i3
295
7 and O\'er__________
412
780
309
124
10 and over_________
246
596
222
55
13 and O\'er_________
167
483
158
25
16 and o'·er__.______
113
398
120
15
19 and over___._____
83
339
92
10
22 and ovcr_________
64
28.'i
5
63
25 and over_____.___
51
240
4
50
28 and o'·cr_________
35
209
37
2
31 and 0\'0'__.______
30
173
1
30
34 and over___._____
23
147
23
o
37 and over_________
17
119
15
40 and ovor_________
14
101
12
43 and over________
10
85
10
46 and over___._____
5
75
8
i ____ _
49 and o\'er_________
4
r.o
52 and over _________
2
7 ____ _
54
2
55 and o\'or_________
45
6
58 and oyer ~ ____ .. ___
2
39
5
61 and o"cr_________
2
32
4
64 and \wer_________
1
26
3
67 and o,'cr_________
1
20
1
70 and o'-er_________
1
17
o
i3 and o\'cr_________
0
14
76 and over.______________ _
10
79 and over______________ __
9
82 and over_________ • ____ __
8
85 and o\"cr_______________ _
6
88 and o"er________ •____ __
3
94 and o\"er_______________ _
2 ----_.
..
100 and over_____________ _
1 ------ ----­
103 and o\'er..___________ __
1 -----Dallas. 'fex., 1914-35: land over_______ __
550
~16
401 1 409
2 and o\"'er___.._____ _
'A?7
435\
3 and o\'cr_________ _
395
2\'3
4 and O\'cr_________ _
347
2iW
2:.'9
194
5 and ovcr___• ____ __
315 I 245
207
169
6 and Q\'er___• ____ __
200 1 224
lSI
148
7 and ovcr________ _
26S ~ 211
169
130
8 and o\"er______ ••__
Q50 I 197
145 : 116
9 and ovcr___• _____ _
240
187 144
100
10 and o"cr__• ___ __
]32 ,
221 I .178
85
II and o\"Cr_________
j4
170
119 '
12 and ovcr____• ____
]05 I
1M
63
13 and over__••_____
144
991
55
14 and over_________
J38
51
95 '
].70
15 and o,'cr __ ._.____
158
132
91
49
16 and ovcr_________
142
40
122
84
17 and ovcr_______ __
119
39
80
18 and over________ _
115
36
77
19 and over_______ __
130 , 1I3
33
75
20 and over________ _
125 ' 105
29
70
21 and over________ _
120
98
2S
I.li
31 and o\"or________
86
59
45
12
41 and ovcr '-______ _
56
37
5
25
51 and o\'er , _______ _
37
23
15
3
61 and o\"Cr_______ _
21
12
12
2
71 and o\'er_______
12
S
o
8
81 and o\"er_______ __
5
7
5
91 and over____ ••___
4
6
101 and o\"er__ •___ __
2
2
Fort Worth, Ta"
lS9IH935:
1 and over________ __
Ti5
600
2 and o'-ef_________ _ 624
~~I 518
495
358
3 and over________ __
569
459
300
"' and o\'"er__ ... __ ..___ ...
417
508
365 1 251
5 and o\'er__•______•
453
384
321
201
6 and ovcr__ •______ _
409
358
286
170
7and over________ ..
342
]52
260
3i31
3 and o\'cr_____ •__ __
343
318
131
239
9 and over.._•• ____ •
226
112
320 '
303 I ~! 211
104
10
and over_._____
o\'cr-----­ __
11 and
201
89
12 Bnd over_____ ._•.
~~U 184 I 81
13 and o\"er.._•• __ __
231 l 1"2 ,
i3
---_
------1----­
3
3
2 _____ _
2 _____ _
1 ____ __ 4
I
3
2
1
o
21 ___________
_
!I
3' ,
----I-
49
2
40
1
39
1
36
30 _____ o
_
30
699
547
U
205
115
18
17
14
13
52
47
449
371
117
322
103
282
77
238
66-, 'I 212
5
183
45
159
142
33
25
125
21
102
20 I' 85
.15
i2
13
63
9
308
223
I
Spring Sum- Au- Wln­
mer tumn ter
---I
1
~i
36
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
TABLE
7.-Frequency distribution of maximum rainfall by I5-minute
intervals-Continued
Rainfall (hundredths
of an inch)
I
Fort Worth, Tex., 1899-1935-Contd.
14 and over.........
15 and o\·er.........
16 and O\'er..__ ..__•
17 nnd o\'er....... __
f~ :~~ ~~~::=::=:::
20 and o\'er._...._.
I
2H
239
229
220
2'21
212
198
192
162
156
153
144
166
113
72
49
28
3i I
151 and o\·er.... __..
19
Amarillo, Tex., 1003­
S
35: 5 1'[
I and o\·er..........
SO,
2 and o\'er........__ 6
' 3 and o\'er.......... 5
4 and o\'er..... __ ... 4
5 and o\·er.......... 3
6 and o\·er.._....... i and O\'er"''''''''
8 and o\'er..........
587
318
9 and o\'cr..........
481
ISS
10 and o\·er......... 463
151,'
11 and o\·er....... .. 363
111,'
12 Bnd o\'er......... 326
00 ;'
13 and o\·er......... 294
1'1'
14 nnd o\·er.........
270
\N
15 and o\'er........ . 246
57
16 and o\·er ........
226
49
17 and o\'er......... 206
45
IS and o\'er......... 198
39
19 and o\'er...__ •• __ 193
35
20 and o\·er......... Iii
31
21 and o\·er......... 165
29
31 and o\'er......... 158
24
41 and 0\'6r......... 150
21
51 and o\·er.._ ..... 138
IS
61 and o\·ee. ' __• __
130
15
iI and O\'er......... 121
14
81 and o\·er.........
114
13
91 and o\·er......... 10i
12
100 nnd o\'er........ 56
4
Dodge City, Kans., 31
Q
1894-1935: 19
1 and o\'er.......... 11
2 and o\·er...__ ..... 5
3 and o\'er......... . 2
4 and o\·er..........
2
5 and o\·er.......... 6 and o\'er.._ ...... i and o\"er..........
8 and o\'er..........
662
146
9 and o\·er.......__•
476
54
10 and o\'er......... 422
41
11 and o\'er.........
361
34
12 and o\'er.........
14
9
5
00
o~er~_________
3i3
o\'er........__
o\'er.._......
o\'er..........
owr..........
323
289
2G4
238
176
159
148
142
134
123
315
306
287
274
257
256
1~
39
II
and O\W......__•
!lnd O\'er.........
and o\·er____.....
and o\·cr..... ____
~}101:~~
g~::~:::::::::
and o\·er....____
r:
361
334
314
291
281
261
200
238
230
217
210
201
191
179
119
81
48
2i
15
4
3
1
5 and
1
~ ~I
c
323
2;
13 and over________ _
293
255
235
218
26
20
18
14
14 and
15 and
16 and
1i ami
o\"er......... o\'er...__....
o\'er......... o\'er.........
g7
jg20 and
:~~ ~~::~::::: ::::
o\'er.........
7
21
31
41
51
61
o\'er......... o\'er. __...... over......... O\'er......... O\·er.........
r:
167
161
146
134
124
115
19 :~~ ~~~::::::::: M~II.
illl~
20 and o\'er.........
104~ 219
96
21 and o\'cr.........
31 and o\'er...__ ..__
55
41
51
61
i1
I
i82
634
5ii
513
459
4382:!,
6 and
7 and
8 and
9 and
o\'er.........
o\·er.........
o\'er.........
o\'er.........
o\'er.........
o\·er.........
68
60'
113
ii
42
22
19
8il
663
609
550
499
459
425
400
3ii
~n~~ :;~~~:::::::::
'
IS inI
sum' Au·
IIII Wichita,
Kans., 100335-Continued.
~ no
~~ 121
~g~
186
21 and o\'er....... __
176
31 and o\·er__..__...
112
41 and o\·er_... __.
69
51 and o\'er._......
42
61 and o\'er..... ••••
28
iI and o\'er____.. __.
15
81 and o\'cr.........
10
91 and o\'cr___ .....
6
100 and o\'er........
2
Oklahoma City, Okla.,
1900-1935:
1 and o\'er.... ......
8.."2
607
2 and o\·er.. " " __'
3 and o\·er__•__.....
554
i and O\'er..__......
480
5 and o\'er..........
420
6 and o\'er..........
362
7 and o\'er...__.....
329
8 and o\·cr__......__
306
9 and o\'er .........
281
10 ",nd o\·er..... ....
261
11 and o\'er.........
237
12 and o\'cr.........
215
13 and over.........
205
14 and over.........
lSI!
15nnd o\·er.........
180
16 flnd o'"er.........
171
Ii and o\'er.........
1&1
18 and o\'cr.........
159
19 and o\'er.........
153
20 and o\·er.........
149
21 and o\'er.........
135
31 and o\·er.........
79
4J and o\·er._......
56
51 and o'l'er._......
26
61 and over.........
14
71 and o\'er....... ".
5
81 and o\"cr.........
4
91 and o\·cr...__ ....
0
100 and o\·er........ .......
Wichita, Kans., 1003-
35: 1 and o\'er..........
ii3
2 and o\'er..........
551
3 and o\'er..........
487
4 and o\·er..........
424
12 and
13 and
14 and
15 and
16 and
17 and
P
•
Spring Sum· Au· j Win· I' Rainfali (hundredths
mer ~I'~i'
of an inch)
211 I
132.
90
52 1
R
4
3
3!
;i 'II
!,
1
j
I
and
and
and
and
and
~l ~~~ ~~:~~::=:::::
91 and o'l'er......__•
100 and o\'er.......
Win.
ter
l
-i--
pr g mer tumn
I
12
S5 'I
00
29 •
I. l'
4
I
0
32
21
14
~
55i
433
360
306
263
238
205
178
161
149
141
123
110
102
93
Si
i9
i2
6i
62
58
30
21
l~4
~I
602
422
366
307
258
215
18i
168
152 132
120
109
0
~
I
0
817
691
612
549
49'J
462
419 1
398
3i1
349
335
305
289
2i6 263
246
234
215
205
189
129
81
51
1I}
32
IS
,
1
3
I
2
1
28
15
i
6
1
465
353
293
259
235
213
ISS
168
158
143
8i
45
36
2S
20
15
o
•
6
5
5
3
3
3
2
2
2
2
2
2
2
2
2
135
122
114
10i
103
89
83
75
68
66
62
3i
21
9
3
2
2
o
o
o
()
o
o
o
906
i23
638
561
499
458
416 :
436
316
65
266
t3
10
I.
222
195
174
148
384' 135
361
331
313
302
28S
o
12'2
S
C-
5
1
\15
lOi
99
94
88
S5
i i i ~1 i8
74 I 235 , 69
69
67
21P I 66
&I
61
215
65
59
199 1 59
32
34
Ii
15
9
42
6
25·
2
4
93
89
2i4
78,
225:
IMI
2
1
o
o
I
1~5 '
3 i
f
i
I
I
1
Oi
2
2
2
2
2
1
I
1
1
1
1
I
I
I
I
1
o
o
(, o
o
37
RAINFALL CHARACTERISTICS AS RELATED TO SOIL EROSION
T.... BLE 8.-11/ean and exlreme nurr.ber of hours, by months, during which precipitation
occurred at the s/ai'ions indicated
Station, period, and
,
indexi~~.:.. F~b.
I I
~
I Mar. _-\pr.! May
.I~I I Ii I "
i
I
I
JulY! Aug. SePt., Oct. !o;ov_ Dec.
Lynchburg, 1002-33:
IHOUro lIouroIHourajHoUTJ" HouraJIIooT. IIour.IIlooro!IIooro ' IIour.11IIow. IIouT6
MlUlmum.___________ 136
107
124
1491 SO
1H
83
98; 121 \157
104
121
~lInJmum____________
39
26
13
14
13 f 12
8,
16 I
6
2
7
32
1
72 ~-68r63;50;49
---a7146" ~ -----s3 45 n
:===1=1=1==1=====
~Iean..--.---.,
Washington, 1905-35:
MlUlmum__ • ________ I 128 \ 114
Minlmum _________ ., "I' 31
27
.
Mean________ •. __ __
141
19
134 i 1221 114
27,
14 I Ii.
T.-\BLE
l
119
15
109
7
121
8
89
14
39
50
42
48
50
71
150 1105
34
28
116
29
134
20
148
181
286
I
j
19 I
130
26
18 i
ii
63
. 56
66
47
1 = 1 = = = 1 =­ = = = = = = =
Elkms, 1905-35:
, !
I
'
)''llUimum.. __ _ __ . f.. 262 I, 295 '. 246 I 2O~. 163
).Iinimum____ ... __ •.. 1 95; 70] 36) 4.
23
:'Iean___
7a
-------- --[--j--I----------
9
~4
76
.----------.l1751IOOl156;1U88
"74 6211---00- 5878112168
..
,
9.-Percentage of rain falling in each hour for storms of 8pecified duration
WASHINGTON, D. C., 11105-35
I
Rainfall during-
Duration
of storm I
(hours)
Season
First
Fourth
bour
Fifth
bour
Sixth
hour
Se\'enth Eighth Ninth
bour
hour: bour
I.'
----1---1-1­
--c
PtrC~~1 perc~II:.~~~~~ :.~~~~~ _~~~~ _~~~~ .:."-'-~~~_ :."-'-~~/'_':~~~
IISPring-------I Summer______
, Autumn •• ____
q
I
Second Third
bour
l, ______ i._ho_ur_ hour
70
52
30 -------- -------- -------- -------- ---------48 ________ - _______ -------- ---- ____ ----------
i..
--------1-------­
--------1-------­
::::JI~~~~~~! ~ I J.-,~ ~ :; :.:~ ~ ;~; ;: : : ~'; : : : :; ·;:;:~: '.;i:~ : I
;.---------.---------------- --­
i
Annual---'_i
SPring-----...
Summer____ ._;
i
49,
24 :
29 ;
16 ;-- ... -- ....----- -'-----' -----_.---j-----..... ----31
13 _______________________________ • __ ~
25
16 ________ • ________• ______________________ __
35;
32 ~
30
'---I Iv:::;:::.:i =! : i
II
SPrlog-----.,,!
29 r
21
Summer____ ...
i
32
_-\utumn ______ l
21 !
29
16_:_ _
23_
II Winter_____ ... I,__
2.~
5
---------1
: . :
21
21
19
I::::::;~:~::.:::.= ::::::::::::
...___
138 1___________________________
_____________ • ____________ . _______
10 ________ • _______________________ _
16:
14 i
21 :
-=-__
22_' _ _
17_
.:.:==. ===,.:.::.:.::..:.:....:..::.:.:.:
Annual... - ~I
2i :--=-'---.E..I__
11_.:..:::.:::.:.: ==..:.::.:.:..:.::.::=-=::.:..:
rISPring ______ . ~
19 ;--15-:~i--17----7-~~-:-:==
1 Summer..__ •
34
~
13 i
I~ J
17
6 --------- ______ ._ . ------­
6.- _______. M~~n---1
~9
I. ,
19
8 ---------________
-.----­
______ ..
12 3 \ . 4
19 :
.1 :'
17
19
12
___________
• ____________
j
i
-'lnnual _____ ~--20----16-;--16-,--18----8-==
;Isprln
Summer. -" -
g ----- - . =
7_______
R
___
.!I Autumn_
Winter.. ____ ..
I
16 I
12 '
9
12
13
24 '
16
17
I
14
15
39
17 .
19
13
17 '
15
20
14
9
16
12
13
7
15)
-==,-==
--------1 ____ .__
__ _
6
9 ________
3 _______.'
8 ________
____ _
__ __ _
AnnuaL .... --12-'--19-1~--15-i--14-,--I1-I---1-~·_==
SPrlng------ .
Summer_.__
Wlnter________
' Autumn _____ .
c _________ ,
j
8 ) - 19 1
12 b 4 1 '
7
13
8
14 l
13 '
15 i
12 l
lq
.
• l
I AnnuaL.. __ - - 9 -
15 '
16
18 '
14 '
14
17
21
15
!
15 1
9 '
12
15
11
7
10
13
1===;"
'!
--
3
__ •___
7
9 -------­
--------
16/--13-;--16----17-1--13-.---10-,--6-:.=:=
-
='
===='========
38
TECHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
TABLE
9.-Percentage of rain falling in each hour for s/orms of specified
duration-Continued
WASHINGTON, D. C., 1905-35-Contlnued
Rainfall during-
Duration of storm
(bours)
I
Season First
bour
I
Second
bour
Tbird Fourtb
bour
bour
Flltb
bour
Slxtb
bour
I
I
Ptrct7lt
!I
Seventb Eightb Nlntb bour I hour
bour
-------1------------1------'
I
1-;':: -;'::i-;':: Perct1lt -;.::
ptrc;::;-;'::I-;::
SPrin g ________
5I
8
8
20
20
16
11
8
4
Summer______
12 !
~
10
9
9
9
16
9
4
71
14
16
13
12
13
8
12
5
Autumn______
g--------- Winter__________6____
11____13_ ___
13____
13____
15_ _ _ _12_ ___
11_ _ _ _
6
j
AnnuaL____
7\
13\
12
15
14
13
11
I
10
5
LYNCHBURG, VA., 1902-33
sprin g ________
Summer______
j
2 --------- Winter________
Autumn______
AnnuaL____
.------ ji~=:::
Sprin g __ •__.__
Summer__ ._._
L __ . ___ .
62
58
38 • _________________________________________ ~------- _______ _
42 _________________________________________________________ _
67
52
33
-------- -------- -------- -------- ---------- ---------------_
48 __________________________________________
.. _____________
------------------------------60
40 ________________ •_______ ._ •• _____ ._. _________ • __ •• __ .. ___ _
=======
~ ~ ~ ,::_:~~ :_~~::-::~~ _ _::--:~::~-I_--C_~:-~ =========
35
40
29
37
18
16
j~;~~~::=:: ~----.!!.I
.\nnual ___ ••
Spring--••••-Summer______
Autumn______
------ ••• Wlnter_____ .__
I
=
35
35
i!
18 •• _...__ •._._. ___ • ___ ••_•••__•__ ._ •• _••••_
7 ___ ••_•. ___ ••__• _____ ._•• __ • __ ._._ •______ _
----.!!. ~=:::::=r:::=:= :::::::::: ==:::::: .:::::::
19
11 ___ •• __•.• ____ • __ •___ •••••• __ ••_._ •• __ •__ _
========~
22
25
15
21
_\nnual_ -.-- - ; -
19
21
26
23
22
24
26
20
23
20
22
24
14
10
11
12
-----:i2 -----;- ------;;- --12-
•..__ •• _ ._ ••••.• _. " __ '_' ._.____ _
•___ • _______ ._.___ _ •_____ •___ •__
_. _________ ._._.__ _______ •• __ •__ _
.• ______ ._ ••• _. ____ ••••• ___ •• _._. _
==..-.-.-.-1== ==
SPring ____._._
11 .
20
23
14
19
13 •• _._ .. __• __ ••_.,_ "_""_ Summer._....
121
31
25
18
9
5 ._ •.. __ ••• ,•••• ____ ._•• _. __ 11.. ____.•• A~tumn-- •••10 .
18 I
25
15
24
8 ... _•.____ -- •• _---.. --- ••• ­
" mter•._. ______
10____
14_:_ _19_,""""::' _ _
22____
12_ ====~.:.:.:::=:l"
j
...--.
91. _....__ ._1 ___ .....\ _.. __ ._
•\nnual_____ _ _11
17 _ _ _18
_ t,_ _22
_1i _ _231
_'_ _ _
_ _ _ _ _ _ _ _ _ ,_ _ _ _ __
SPring ___•____ ----14-1--19-1--1-6 ~--1-5
Summer..____
22 i
25
15
22
10
7
Autumn______
19,
16
16
16
13
• --.--- •• Wlnter....._____
14_1_ _
13____
16____
19_
j
.\nnual..___
11_:__
17 I
191
15
I
17
14
181-------511~== 4
2 ..... ___ .....__ 15
5 t.... -.-.•-..... . 17 _ _ _10_1':':':::=:':':':::=:
131
5
1 .. ,. _.....__
SPrln g . ____ .._
16 !.
19 i
11
10.
10
14
12 :
81 __ ...... Summer--.-..
15 :
21
8
14
10
9
16
7 ........ 8
Autumn......
12!
9
12
11
19
20
10
7 - -'''­
....----- Winter•.•_______10_:_ _
11__ ~ _ _10_ ___
11____20_ _ _ _13_.1_ _11_..:.:.:.::.:.:
j
_\nnual ___..
14 :
SPrin g .. ______
9
Summer.. __ ._
14 :
Autumn __ ... _
9 1
g
• "'-- - Winter•••. ____ _ _
Ij .\nnual .. __ •
15
10
11
10
I
11
13
6
11
1
!!
I
11
12
16
i
12 I
t
10
I
11
I
i _'.'_'.
I
13
14
15
10
11
5
10
10
16
18
9
6
10
14
11
16
12
7
10___________
11
13
~ _ __
13 _ _ _
5
7_"----=.. _::.1__
9
9
11
12
a
14
121
7
39
RAINFALL CHARACTERISTICS AS REI,ATED TO SOIL EROSION
9.-Percentage oj rain Jalling in each hour Jor 8torm8 oj 8pecified
d1lratiofl-Con tinued
TABLE
ELKINS, W. VA., 1005-35
Rainrall duringDuration
of storm
(hours) Se8S0n
First
hour
I
2
1
}'I!th
hour
Sldh
hour
Seventh Eighth Ninth
hour
hour
hours
Percent Ptrcent Percent Percent Percent Percent -;::;:::; Percent;;;:;;;
~~~Jier_-:=:::
~
1--I.l!tumn.-.--.
.--.•• --. WIDtcr._ ..•_..
~~
59
:::::::: :::::::: :::::::: .::::::: .:::.::::: :::::::: ::::::::
41 .-----.- ----.--. -.-... . .•••• -- •• - ..•..••..- ••. -- .-••••-­
44 __ ••• ___ ._._. ___ ._._. __ •..•__ , ................ _.•.••.. __ 56
AnnuaL __ •• --59-1--41-~~~~========
Spring_. ___ .••
Summer ___..•
umn - •. --.
3_________
nter•..• __ •.
=
1
=23=
====
==
32
45
___ •• _•• ,_._ •• _, .•••.•
• .•• _._._ •• _____ _ ,\W
AnnuaL.___
4
Second Third Fourth
hour
honr
hour
I!I~~~~er::::::
I
40
18 __• _____ •__ ..... ""'"
47
39
Ii ____ • ___ .-•• - •••.•. - ..•...• - .•••••• -.-.--- -----.-­
26 ___ ._.__ •__ • __ ••..•. _._ • . . _••• , .••.•••. ____ .... __
.••. _........___••••_. __ _ g11
26
gl28
-------------------,---------39 43
18 I " " ' " ._ •.. _.. ' . . . . . . . . . . . . . . . ___ . _______ __ ____
...--.- .. Al!lumn..
WIDter_...___
AnnuaL____
42
36
35
30 1:
if! l~ I:::::::: :::::::,":::::::::1:::::::: ::::::::
2i '.
25 i
2i
19
18 -__.....-...• __ '--"--'_""" ."""'"
__ .....- .--.---. ____ • __ '.•.---__ ' __
- -321
-1
- -15- - - - - -1 ·......
- -1..___
' -..t
30
23 I
_ ...-__.__
g
SPrin -------Summer••
____
5
Autumn ...___
• -------- Winter..•_____
I S A.nnuaL_ .. _
prlng. _____ ..
Summer..---e
Autumn_. __..
--.--..-. Winter________
==,-===1====
1 . . . . . __ · • • • _ •••
-'-~---'-;-1
~~~1'r-1-12
331
22
14
_1 ,
\0 -------- • ____ ._. __ •.•----- --.----.
19
26
25
20 ;
10 ________ •• __ .... _,. •• _______ . __ •••
19____
21_. _ _20_, _ _
18_ --... ---1..:::.:::.:.::..:..:: ..... ---1:::.:.::..:..::
--=-t__
25
Ii.
I
22
14
121
23.
25
25
25
19 i.
19,
14 I
26
23
20 :
21 :
15 :
15
15 II
18\
12 ~I~j::..:..:..:..:::::.:::::.:
12
121__________' "_" ______ ...
15
".-_."
-......
11
99 •-·.·-.----i
_________ 1•••
__ . . _____ • __ _
17
10 __ . ___ ..•_:. __ .. ___ ..... __
--.==
-.---I=
== '==1-....
!'==I-::::-:-:-
i
_-I.nnual-..__
17 ; 24
19 '
16 I
14
10
'ISPrin g .----.-- -1-31--1-71--1-21--1-5l----r7--1-7: - - - 9
Summer.. ____
19 i
171
18 f
18 :
11
11 i
6 -------- .• - .... .
Autumn ____ ._
16 '
IS
14 ,
12 I
16
14
10 ___ . ____ 1__.....
7--------- Winter•. ____ .. _ _
15_1_ _
15____14_1_ _
15_!_ _
17____
14_!___1_0_!.:.:.=.:::.:.:.=.:::
l
AnnuaL ___ . _ _
17_i_ _
17_ _ _1_51_ _16_1_ _
14_!_ _1_3._ _ _8_t-..
sp. dng ______ .• --14-\.--15- -rrj'--14-'--13-1--14- j- - - l - l1--6Summer.. ____
13,
15
1/
11
12 I
13:
!O r
9 ------ .• S.....____ A~tumn--.--12:
16 ,
15
10
221
sIlO.
i ... ____ _ "mteL._____
11 :
20
19 :
10 ,
9
13 .
10 I
S 1._.____. I
•
A~nuaL.---
sprm g - ------Summer______
Autumn.. ____
\I --------- Winter..
___ .._
I
I
I'
TABLE
AnnuaL____
13 ;
12 ,
15 I
19 1
11
I
I
15 !
14 '
11
11
13
. '
i
I
16
13
12 ,
11 I'
14
11
1~_;
13 .
10 ;
15 I'
121'
10
13
141
I
11
' I
I
13
12 ,
14
10
10
10 '
12 '
7
9 .
12j'
S ,_ •. ____ _
~
9
11
7
10 ;
7
4
7
-----------------------,---1--14 I
12
12 : .13 i
12
12 I
10 ,
9
6
lO.-Number of occurrences oj intervals with.out measurable precipitatifJ1l
Length or interyal
(days)
- - - - - - - - 1 - - - - - - - ---11---------1--- - - - - - Washington, D. C.,
1905-35:
1 and more_______ __ 2 and more. _____.. _
3 and more......__ _
4 and more________ _
5 and more_. ______ _
6 and more. __• ____• 7 and more.. _. ___ __
Sand more..__ •__ __
9 and more_...... __
10 and more_____.._
11 and more.._____ .
12 and more.. ______ ,
608
454
328
660
465
322
234
156
109
110
72
73
48
46
31
27
20! 20
14: 13
11'
6
229
164
496
382
2.16
251
196
154
l1S
86
65
51 !
37 .
30
Washington. D. C., 1005-35-Continued.
13 and more.. _____ _
14 and more. . ____ _
15 and more .. __ ._._
326
16 and more, •.. __ __
228
Ii and more.... ___ _
173
18 and more.. __ •___
114 19 and more.. _____ _
~l
20 and more.._.. __•
23 and more____ ... _
39 H
25 and more. ______ _
31 Ii
2i and more..____ __
19 'I
28 and more______ __
15 il
579
451
10
5
4
3
3
1
1
1
3/ 1
2
1
2
0
2 t __ • __ _
2 .. ____ _
1 ....._
oo 1_____ _
23
16
12
8
II
7
9
6
9
4
7
3
6.
2
6
1
5
4 : ....
2
1 :::.::
40
TE'OHNICAL BULLETIN 698, U. S. DEPT. OF AGRICULTURE
TABLE
lO.-Number of occurrences of intervals without mea8urable precipitation­
Continued
Length orIntervaJ
(days)
I
Au·
Spring Sum·
mer tumn
Win·
ter
, - - ---
Lynchburg, Va., 1002-
33:
land more••••....•
563
2 and more_________
443
3 and more_______ ._
333
4 and mOTa__ •• _._._
247
5 and more.________
165
6 and more_. __ ._. __
123
7 and more___ • __ •••
84
8 and more _________
65
9 and more_________
45
10 and mOTe________
34
11 and more________
22
12 and more._______
14
13 and more________
13
14 aud more._______
7
15 and more._______
5
16 and more________
4
17 and more________
4
18 and mOTe________
4
19 and more________
4
20 and more________
2
21 and mOTe._______
2
22 and more________
1
23 and mOTe._______
0
25 and more________
0
26 and more________
0
30 and more________
0
Elkins, W. Va., 190535:1 and more_________
713
2 and more_________
435
3 and more_________
249
4 and more_________
147
5 and more_________
82
6 and more___ ._. ___
49
7 and more_____ ••__
27
8 and more_________
15
9 and more_________
12
10 and more________
1~
11 and more_____ • __
8
12 and more___ •• ___
4
13 and more____ • ___
3
14 and more________
2
15 and more_. ______
1
20 and more______ ._
------Dallas, Tex.,1914-35:
1 and more_________
421
2 and more_________
301
3 and more_____ • __•
245
4 and more_________
187
5 and more_________
148
6 and more. ________
115
7 and more_________
88
8 and more_________
70
9 and more_. _______
53
10 Bnd more________
42
15 and moro________
9
20 and more________
3
25 p,d moro________
3
30 aud more________
1
35 and more________
1
40 and moro________
1
45 and moro________
1
Fort Worth, Tox.,
1899-1935:
1 and more_________
705
2 and more _________
525
3 and mOTe.________
427
4 and more_________
344
5 and moro_________
275
6 and more_________
216
7 and moro_________
173
8 and more_________
142
9 and more_________
114
10 and more________
86
15 and more________
23
20 and more._______
12
25 end more________
6
30 and more________
5
045
436
316
215
142
104
71
47
34
26
15
12
8
8
7
4
4
4
2
2
2
2
1
0
0
0
419
352
295
241
196
161
130
101
82
66
54
44
37
29
25
20
16
13
13
12
12
8
7
5
4
1
690
466
292
190
115
71
44
28
10
7
5
4
2
0
0
------ --
584
414
288
207
151
108
75
60
547
444
328
230
167
125
98
65
46
39
32
25
20
12
9
7
5
3
3
2
1
1
0
0
0
0
702
414
231
121
61
29
20
11
6
4
41
29
24 -._--21 -----13 -----11 -----7 -----4 ------
301
307
36S
216
230
276
169
193
228
147
170
190
118
143
155
112
117
123
98
94
98
82
86
80
72
76
65
61
70
53
22
27
30
22
12
6
12
2
1
5
1
0
2
0 -----1 ------ -----1 ------ _.. _--527
389
333
284
231
195
170
144
131
111
52
29
15
7
494
361
314
276
246
210
183
164
148
135
62
32
14
S
509
379
319
273
237
201
159
133
1H
9.~
50
21
8
6
Length of Interval
(days)
Fort Worth, Tex.•
1899-1935-Contd.
35 and more•...•• __
40 and more________
45 and more________
Oklahoma City, Okla.,
190IH935:
I and more.___ .. ___
2 and more_________
3 and more_________
4 and more_________
5 and more_________
6 and more_________
7 and more_________
8 and more_________
9 and more_________
10 and more________
11 and more________
12 ana more________
13 and more________
18 and mOl'e________
23 and more________
27 and more ________
Wichita, Kans., 1003­
35:
1 and more_________
2 and more_________
3 and more_________
4 anrl more_________
5 anti more_________
6 ana more_________
7 and more_________
8 and more_________
9 and more________ •
10 and more. ___ ._._
11 and more____ • ___
12 and more________
13 and more_. ______
18 and more________
23 and more______ ._
27 and more______ ._
Amarillo, Tex., 1903­
35:1 and more _________
2 and more_________
3 and more_________
4 and more_________
5 and more.________
6 and mOTe.. _______
7 and more•• _______
8 and more_________
9 Bnd more_________
10 and moro____ • ___
15 and more________
20 and more________
25 and more________
30 and more________
35 and more________
40 and more________
45 and more________
Dodgo City, Kans.,
1894-1935:
1 and moro_________
2 and more_________
3 and more_________
4 and moro_________
5 and moro_________
6 and more_________
7 and moro_________
8 and moro_________
9 and moro_________
10 and more________
15 and more________
20 Bnd more________
25 and moro________
30 find more__ . _____
35 and more________
40 and mOTe________
45 and more________
50 Bnd more________
Au· Win·
Spring Sum·
mer tumn ter
------
5
4
2
3
1
1
4
3
0
628
454
3n
49
39
16
7
2
492
438
329
262
212
167
139
U7
99
84
72
60
50
23
U
7
467
358
298
252
215
1M
152
132
102
83
71
60
557
401
321
242
186
148
113
88
71
59
47
37
31
8
3
2
609
429
313
245
195
150
114
92
75
62
48
40
33
17
8
2
457
334
269
217
182
157
126
101
86
519
358
301
246
209
184
161
130
114
99
40
20
13
10
9
8
5
618
435
331
258
212
178
138
112
93
651
476
817
572
433
351
282
214
163
125
98
292
243
188
145
U8
92
69
66
383
294
238
191
157
-123
105
86
44
30
24
22
18
18
17
16
77
32
15
5
0
0
0
0
77
22
5
2
2
2
2
1
1
66
31
17
9
77
65
55
48
29
9
2
~I
234
200
172
160
135
118
100
93
47
24
15
6
2
1
1
429
326
281
243
218
192
166
148
132
U6
59
34
19
8
3
1
1
0
4
1
()
315
268
2411
204
182
160
140
122
100
92
81
73
62
36
21
17
215
162
132
112
97
80
64
58
48
46
41
37
33
28
18
lo4
256
210
186
167
147
122
115
110
104
94
59
39
29
23
15
9
5
235
199
175
153
132
120
107
97
84
74
46
35
21
19
6
3
3
2
TAll1,E
11.-Diurnal variation in the
IL1/WU1It
of 7I!Cl!8urIlble 7Jrccipilal'ion I
WASIIINO'l'ON, D.O., 1905-35
OIock hour ondlng atMonth
1
0.001
Inch
1anuary•••••••••••
February__ •.••_••
Marcb••••••••••••
t/.:rU•••••••••• - •••
ny._ ............
Juno••••••• _••••••
July•••••• _. ___ •. __
AUb'Ust••••••••••.•
September._ •.• _••
October.••••.••• __
November••••••_.
December..•••••••
14
13
12
13
16
16
14
14
14
12
11
13
4
6
_31_ _51_
~
0.001 0.001
Inch Inch
14
14
13
13
13
13
13
14
12
14
13
10
9
12
12
11
12
13
12
!3
12
12
14
13
0.001
Incil
14
13
13
13
11
9
9
10
8
10
10
1:1
1).001 0.001
Inch Inch
14
14
13
13
14
13
13
14
12
11
g
9
lj
8
10
10
12
11
9
10
10
10
13
13
10
11
Noon
1
0.001 0.001
Inch inch
14
14
13
13
0.001
13
9
8
10
12
11
0.001
Inch
14
12
13
13
11
10
0.001
12
9
8
9
12
12
10
11
14
0.001
Inch
13
12
13
13
10
8
10
13
12
10
II
13
8
7
0.001
in~h
14
13
16
14
11
9
7
10
13
11
11
14
9
14
13
10
8
8
11
13
12
11
14
14
Incl.
13
13
14
10
11
13
11
14
14
11
11
14
Inch
13
12
13
13
12
15
17
17
16
15
11
13
2
3
4
5
6
7
8
U
10
11
O.OO! 0.001 0.001 O.OO} 0.001 0.001 0.'101 0.001 0.001 0.001
Inch Inch inch inch Inch Inch inch Inch inch Inch
12
11
11
11
11
11
12
12
11
11
12
12
12
12
12
12
11
11
11
11
13
13
13
13
14
15
15
14
11
12
14
19
19
13
16
17
19
14
13
16
14
20
16
17
17
22
24
24
22
19
29
30
23
27
29
20
30
25
17
19
32
25
30
33
34
32
32
22
27
18
29
28
29
29
29
18
24
30
25
22
18
20
22
22
23
19
16
22
18
21
13
15
11
11
14
14
14
15
15
12
10
11
11
11
11
11
10
11
10
11
10
12
11
11
11
11
11
10
10
11
Mid·
night
0.001
Inch
13
12
11
13
15
16
16
15
14
11
10
12
~
~
~
~
t;:j
E:l
~
o
Ul
~
~
LYNOIIDURO, VA., 1002-33
Jnnuary.••..••••••
February_••••••••
March •._•••••• _••
~r1L•••­ ••••••••
ny••••.•.__ •••••
June•••_._........
1u1y•••••••"." ••,
August•••••••••.••
SOllteInber••••••••
October•••_•.•••.•
November••••••.•
December.........
10
11
10
12
12
13
12
12
13
12
11
12
12
11
13
13
12
10
11
10
13
13
15
12
9
9
9
9
9
9
10
10
10
10
11
11
11
11
11
12
13
12
12
12
12
14
13
10
14
13
14
13
14
14
12
8
8
9
10
10
12
12
13
12
8
7
9
10
10
12
8
10
11
12
11
11
12
13
-­ ---------
I
14
14
15
12
8
7
Tho numbers shown represent mean smoothed vnlues.
14
13
14
12
9
8
8
9
11
13
12
13
14
13
13
12
9
9
8
8
10
12
12
13
14
12
13
11
8
8
9
8
9
11
12
14
13
12
12
11
8
8
9
9
10
10
11
13
121
11
11
11
9
II
11
11
9
9
10
12
12
11
11
12
12
12
14
13
9
8
10
12
12
11
11
10
11
15
17
16
11
9
13
17
18
20
19
13
10
10
10
10
10
13
19
23
24
20
15
12
11
12
11
11
11
12
14
10
11
10
10
12
21
29
27
21
17
14
11
Jl
10
10
10
10
12
21
10
10
13
20
27
29
25
20
30
29
23
19
15
10
10
14
9
9
10
10
11
Iii
20
23
25
22
18
14
10
9
10
10
11
15
19
21
21
19
15
12
10
9
10
10
10
11
12
12
14
18
21
19
15
12
13
16
19
20
18
14
11
11
10
10
10
10
1o
1
1
1
1
1
1
1
1
1
1
1
I
8
o
Ul
~
!....
o
!2l
..
~
TAli),.] II.- -Diurnal v(uiation in Ihe amount oj measurable precipitation L-Uontinued
~
ELKINS, W. VA., 1005-35
~
Olock hour ending at---~
MOllth
.j
1
:J
4
II
5
7
I
8
U
IO
II
Noon
1
~
@
:I
4
5
6
7
9
8
10
Mid·
night
11
--- - - - - - - - - - - - - - - - - - - - - -- --- - - - - - -- - ---- - - - - - - - - - OliO/ 0.001 0.001 0.001 0.0')1 0.001 0.00/ 0.001
January••••••••••.
February .. _••.••••
March •• """""
ApriL•••• _._ ••••••
May..............
Juno•..••••••.••.•
July...............
August•••.••.•.••.
September•••.•.••
October..•••.•••••
NOvClnbcr.•••••.•
Deccmhor.........
Inch
15
15
16
16
16
16
15
14
15
13
12
14
I
inch
)6
16
17
16
16
17
15
15
16
14
13
15
inch
17
Ii
18
16
16
19
18
17
Ifl
14
13
16
inch
18
18
19
17
17
20
2()
18
16
13
14
17
incl.
18
18
19
17
17
10
III
17
15
14
14
18
inch
17
17
18
Ii
16
18
18
inch
16
:7
\(\
I
14
14
14
17
I
18
17
15
17
18
17
16
14
14
15
inch
15
15
17
17
16
17
18
10
18
14
13
14
0.001 0.001 0.001
inch inl!h inch
13
15
17
17
Ii
17
18
18
15
13
12
13
14
15
17
17
17
17
17
16
13
12
13
14
15
15
17
16
16
17
17
16
13
12
14
15
0.001
incl.
15
14
15
15
16
inch
14
13
inch
15
1:1
13
16
23
26
25
inch
15
13
13
17
23
27
25
20
20
20
15
12
13
15
15
12
13
15
15
13
13
15
14
15
19
19
20
23
18
14
12
14
15
..
--------
0.001 0.001 0.001 0.001 0.001 0.001
_­
20
----
Inch
15
13
14
19
24
29
28
22
15
13
13
15
inch Inch
15
15
13
14
15
16
21
20
26
25
32
31
34
:14
25
26
16
17
13 , 13
1~
121 13
14
------
0.001 0.001 0.001 0.001 0.001
0.001
inch
16
15
15
18
22
27
30
24
17
15
12
13
incl.
16
16
17
18
17
16
16
----
inch
16
15
15
17
20
24
26
22
17
14
12
13
'----
inch
16
15
15
17
18
22
24
21
17
14
12
14
inch
17
15
16
17
18
20
21
18
16
14
12
15
inch
17
16
17
18
18
18
18
15
13
12
12
15
14
13
12
12
15
----_.­
.. lly. _____________
JUliO••••••••.••••.
July.••••••.•• _.•••
August••.••..•.•••
Soptmnher..••••••
Octohcr...........
November•.•••.•.
December•.•..••••
8
7
10
18
24
22
7
5
9
12
12
10
8
8
12
22
10
9
14
18
9
7
23
25
17
9
9
10
11
12
13
12
13
12
20
11
._"
11
10
13
21
22
14
8
9
12
12
12
11
10
11
13
18
10
10
12
19
21
14
7
9
12
20
121
11
10
I
14
8
9
12
13
11
10
11
12
14
17
18
14
8
8
10
11
13
16
16
11
IO
7
8
0
10
10
10
11
10
10
­
10
10
11
13
14
10
8
9
10
10
10
10
11
10
9
11
12
10
9
0
10
11
10
10
12
10
10
12
12
10
10
10
10
10
10
10
11
10
11
13
14
t4
12
12
11
10
9
10
11
11
12
13
15
15
12
13
13
10
10
11
~
b:I
~
t:<:l
~
2:
0>
<C
.Y'
~
~
DALLAS, TEX., 1014-35
January." ........
Fobruary ..••••.•.
March ............
Urn••••••••••••.•
2:
....
11
10
12
12
13
12
11
12
13
12
11
11
11
0
11
12
14
13
14
14
14
14
12
11
10
10
101
9
9
9
9
12
15
14
15
16
14
12
9
12
16
15
14
15
14
10
11
10
a
11
10
9
13
11
17
18
14
12
20
20
14
11
14
11
10
10
12
11
9
9
13
10
9
10
13
19
19
13
8
7
9
10
8
8
8
9
12
17
18
12
7
6
9
11
9
8
7
8
13
18
17
10
6
6
7
8
13
20
20
12
6
6
11
11
14
11
8
14
11
8
8
8
11
19
23
16
6
5
10
12
12
9
~
~
~
~
a
81-3
q
~
FOWl' WOn-I'U, 'I'EX., 18111H935
._--......
---.~
January___________
February_________
Murch ____________
rIL___
----­
-------­
ay
• __ •__
• ___ •
June. __ •___ • ______
July_. __ •__________
August..__ •____ ...
September________
October____ •______
November________
December_________
tl:
6
7
II
18
18
11
7
8
11
12
9
8
7
7
II
18
19
13
8
11
13
14
12
9
7
7
to
16
18
12
9
12
14
15
12
\I
7
8
8
14
15
12
10
13
14
14
12
8
8
8
10
13
14
12
8
8
11
15
16
11
10
10
13
13
9
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January___________
February. ________
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... _. _________
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June. _____________
July ________ .. _____
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October_. _________
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