Richard W. Dixon and Todd Moore
Department of Geography
Texas State University – San Marcos
May 2009
Study Area
Texas occupies about 7% of the area of the US.
Second largest state at 692,000 sq. km.
Lat Range: 25.83N – 36.50N (1289 km)
Lon Range: 93.52W – 106.63W (1255 km)
Elev Range: sea level – 2667 m
Physical Regions: Gulf Coastal Plains, Interior
Lowlands, Great Plains, Basin and Range Province.
 Climate Types: Cfa, BS, BW
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Data Sources
 Temperature and Precipitation: 1932 – 2002.
 US Historical Climatology Network
 43 stations with long-term records.
 Corrected for time of observation and identified
inhomogeneities.
 Not fully homogenous spatially.
Data Sources
 Bulk Evaporation: 1954 – 2007
 Texas Water Development Board
 Blend of pan measurements and modified Penman
formula computations.
 Gridded to 1 x 1 lat/lon
Texas HCN Stations
Miami !
Muleshoe
! Plainview
!
Clarksville
! Crosbyton
!
! Haskell
! Seminole
! Greenville
! Weatherford
! Albany
! Snyder
! Dublin
! El
Paso
! Pecos
Balmorhea !
! Ft.
Lampasas
! McCamey
Stockton
!
! Llano
Marshall !
! Corsicana
! Brownwood
! Mexia
!Temple
Brenham
Blanco
!
!
New Braunfels
Boerne!
!
!
! Flatonia
!
!
San Antonio
Luling Hallettsville
! Alpine
! Liberty
!
! Eagle
Pass
!Beeville
! Encinal
Alice
!
!
Falfurrias!
!
Rio Grande City
0
125
250
500 Kilometers
Danevang
Corpus Christi
Data Processing
 Less than 1% missing in temperature and precipitation
estimated by neighbor regression.
 Evaporation 100% complete.
 Monthly data also aggregated to seasonal and annual
values.
 Winter (D,J,F) Spring (M,A,M) Summer (J,J,A) Fall
(S,O,N).
Annual Precipitation Trend (mm / Year)
(POR 1932 - 2002)
Annual Temperature Trend (C Deg / Year)
(Various POR 1932 - 2002)
+ 1.869
!
+ 0.007
!
-0.013
!
-0.013
+ 2.926
!
!
-0.010
+ 2.674
-0.012
-0.009
!
-0.014
!
!
!
!
-0.017
!
+ 0.015
!
-0.011
!
-0.008
!
+ 3.620
-0.012
-0.012
!
!
-0.007
!
!
+ 3.943
!
!
+ 2.747
!
+ 4.178
!
-0.011
!
+ 2.533
!
+ 0.026
!
+ 0.013
!
0
125
250
500 Kilometers
0
125
250
500 Kilometers
+ 5.620
Spring Precipitation Trend (mm / Year)
(POR 1932 - 2002)
Spring Temperature Trend (C Deg / Year)
(Various POR 1932 - 2002)
+ 0.020
!
-0.017
!
+ 0.019
!
!
-0.021
!
+ 0.020
-0.019
!
+ 0.035
!
-0.013
-0.012
!
+ 0.020
!
+ 0.012
!
!
+ 0.011
!
0
125
250
500 Kilometers
0
125
250
500 Kilometers
Summer Precipitation Trend (mm / Year)
(POR 1932 - 2002)
Summer Temperature Trend (C Deg / Year)
(Various POR 1932 - 2002)
-0.020
!
-0.020
!
-0.017
! -0.020
-0.020
-0.016
!
-0.014
+ 1.682
!
!
!
+ 0.013
!
!
-0.010
-0.012
!
!
-0.018
!
-0.017 -0.017
-0.012
!
!
!
+ 0.006
!
-0.028
!
+ 0.035
!
+ 0.016
!
0
125
250
500 Kilometers
0
125
250
500 Kilometers
Fall Precipitation Trend (mm / Year)
(POR 1932 - 2002)
Fall Temperature Trend (C Deg / Year)
(Various POR 1932 - 2002)
-0.015
!
!
+ 2.437
-0.017
!
!
+ 1.565
+ 1.829
!
-0.020
!
-0.012
-0.019
!
!
+ 0.016
!
-0.017
!
+ 2.960
+ 0.017
-0.019
!
!
+ 1.770
!
!
!
+ 1.592
!
+ 2.301
!
+ 0.012
!
0
125
250
500 Kilometers
0
125
250
500 Kilometers
+ 3.360
!
+ 1.845
Winter Precipitation Trend (mm / Year)
(POR 1932 - 2002)
Winter Temperature Trend (C Deg / Year)
(Various POR 1932 - 2002)
-0.019
!
!
-0.023
!
+ 0.015
-0.015
-0.015
!
!
+ 0.045
!
+ 0.026
!
0
125
250
500 Kilometers
0
125
250
500 Kilometers
January Precipitation Trend (mm / Year)
(POR 1932 - 2002)
January Temperature Trend (C Deg / Year)
(Various POR 1932 - 2002)
!
+ 0.023
+ 0.058
!
0
125
250
500 Kilometers
0
125
250
500 Kilometers
August Precipitation Trend (mm / Year)
(POR 1932 - 2002)
August Temperature Trend (C Deg / Year)
(Various POR 1932 - 2002)
-0.024
!
-0.015
-0.026
!
!
-0.017
-0.020
!
!
-0.023
+ 0.772
!
!
-0.022
!
+ 0.013
!
-0.013
!
-0.016
!
-0.017
!
-0.015 -0.017
!
-0.013
!
!
!
-0.011
!
+ 0.010
-0.030
!
+ 0.031
!
+ 0.016
!
0
125
250
500 Kilometers
0
125
250
500 Kilometers
Comments on Precipitation Trends
 Mixed signal in temperature.
 Eastern areas cooling in summer and fall
 Western areas show greatest rates of warming in
spring. Large warming trend in Rio Grande Valley
winter.
 Annual trend more cooling than warming but distinct
spatial pattern.
Comments on Precipitation Trends
 Only seasonal trend identified is in fall with increase
in pcp. in eastern and central area.
 No other seasons show trends.
 Annual trend mirrors fall season trend
 October positive trends dominate.
 Only two stations show month with negative trend.
Comments on Evaporation Trends
 Panhandle region dominated by increased evaporation
in all seasons.
 Far west and Rio Grande Valley shows decreasing
trend.
 Winters show more evaporation spatially while
summer pattern more mixed.
Conclusions
 Results (kind of) track with NAST report of 2001.
 Some warming is occurring but most likely at low-end
of early model scenarios. Eastern cooling trend
anomaly.
 Precipitation more problematic and drying not shown
in panhandle.
 Evaporation matches well with model ppt.
Future Work
 Examine trends and changes in rain days and rainfall
intensity.
 Examine trends in humidity (mixing ratio).
 Correct evaporation data for land use/irrigation use?
 Potential sea surface temperature contribution?
Acknowledgements
 US Environmental Protection Agency for grant
funding.
 Becky Brown, Sayali Gokhale, and Susan Street of TX
State for assistance in data processing and mapping.
 Texas Water Development Board
 NOAA/National Climatic Data Center
 Legions of weather observers!
Questions?