THE HYDROSPHERE AND THE HUMAN ENVIJXONMENT
An introduction to some hydrolagical aspects of international research
programmes om problems of the h u m o emvironment
K. SZESZTAY*
President of the International Association of Scientific Hydrology
Throughout approximately one million years of history, the basic attitude of man
towards his environment was accommodation. Over the last two centuries this
situation began to alter and now man is actually changing his environment to a rapidly
increasing extent. The immense significance of this period of change in relation to
future conditions has been known for a comparatively long time,but an appropriate
social and international awareness has begun to develop only during very recent years
(ECOSOC 1968,ICSU 1969,UNESCO 1970a).
A comprehensive study of the hydrosphere as a component of the global
geophysical system, and as a basic element of the human environment was hindered
for a long time by lack of data. It was also hindered by the difficulty of achieving an
integrated solution of basic equations describing processes on a global scale. Now,
during the last few years,a possible framework for co-ordinated data collection and
research has been created by the InternationalHydrological Decade and by the Global
Atmospheric Research Programme. Principles of a theoretical approach have been
explained (Dooge 1968), and during a recent symposium on the world water balance the
possibilities of computerised mathematical modelling of the atmospheric phase of the
global hydrological system have been demonstrated (Manabe and Holloway 1970).
Limiting factors on further development are the formulation of meaningful concepts
describing the basic features of the global hydrological system and its subsystems,and
also the collection and synthesis of data required to build and fit the models.
STATISTICAL AND
DYNAMIC
CHARACTERISTICS OF THE HYDROSPHERE
The hydrosphere may be described as a geophysical system consisting of four principal
parts (terrestrial, atmospheric, polar and oceanic subsystems) inter-related by large
scale movements and transformation processes,governed primarily by solar energy.
Static Amounts
Estimations of the four principal components of the hydrosphere are summarised in
Table 1.
The total water resource of the Globe is considered to be constant in terms of
human history. Relatively little is yet known about its origin and variations during the
geological history of our planet (Fedoseev 1967,UNESCO 1970).
Estimations of present water amounts in the world ocean, in polar ice caps,in
surface waters and in the atmosphere are based on measurements which assure
reasonable accuracy. Estimations of the total amount of groundwaters are much more
difficult,and in this respect even the orders of magnitude may be questionable.
.
* Research Institute for Water Resources Development,Budapest, Hungary.
455
K.Szesztuy
sp
TABLE
1 Review of Estimation of Princi al C m onents of the Hydrosphere. Total water resources
of the Globe are approximately 1.5 x 10 km
B
Aren cvvered
World ocean
Polar ice
I
I
I
I
Terrestriol waters
Atmospheric waters
(0 UNESCO tg70
ORV/G 1970
(3)
LVOVITCH 1970
: Groundwofrs 64000
Soil moisture
82
Lokes 230
Rivera 1.2
L o n g - T e r m Variations among the Components
Climatic changes m a y considerably affect hydrological conditions. Towards the end of
the last glacial period, about 18,000years ago, the sea level was some 105 - 120 m
below the present level (Orvig 1970). This change in level represents a water volume of
40 x 1 O6 km3.If it ‘is true that all this volume was stored in the form of ice, then the
total water equivalent of the polar ice caps and glaciers was about three times greater
than at present.
Recent Variations among the Components
Measurements indicate that the total amount contained in ice masses is increasing
during recent times. The measured net increase of 500 km3/year, giving about
40,000km3 for the last 80 years, is the result of an increase of 600 km3/year in the
Antarctic and an approximate decrease of 100 km3/year in the arctic ice (Orvig 1970).
World sea level showed a rise of about 0.2m for the 5 0 years ending in 1940 and a
40% decrease in rate of rise since then (Orvig 1970). If this rise in level is caused by an
increase in the total amount of water stored in the world’s oceans - as assumed in the
last column of Table 1 - the question arises: what is the source of the recent increases
in total water equivalent of both the ice masses and the world’s oceans?
The data in Table 1 indicate that groundwaters are the only source which could
correspond with the increase shown above, of 140,000 km3 during the last 80 years,
i.e. an average rate of 1,750 km3/year. If w e consider the total amount of
approximately 2,800km3/year taken for agricultural,industrial and municipal water
uses (Table 4) and also the great amounts of groundwater explored for mining
purposes, it is reasonable to assume that groundwater exploitation has a significant
role in the world water balance. Exploitation of non-recharggd groundwaters at the
above rate of 1,750km3/year would mean about 1 m in water layer depth,i.e. about
5 m depletion in groundwater levels during the last 80 years for the total land areas as
an average. The extreme complexity of the processes of the global hydrological system
dictates, however, that any relation of the increase of water in the oceans and the
polar ice to the man-caused groundwater depletion should be considered as one, but
not the only possible, explanation of these changes.
456
T h e hydrosphere und the h u m a n environment
T h e D y n a m i c s of the Hydrosphere
Relative amounts and interrelated fluxes of the four principal parts of the global
hydrological system are shown in Figure 1 according to a scheme presented at the
World Water Balance Symposium (Reading 1970) by E.Eriksson. The data indicates
that - as in other parts of the geosphere and biosphere - there are sharp and reverse
asymmetries among the static and dynamic characteristics of the four components of
the hydrological system (Kalinin and Szesztay 1970).
Afmospberic waters
Y
Y = 24000x/03km3
A V = 500 kd/e'V
J = /SOOD yeurs
= 13
403km3
V- 64000 x 4D3km3
+
Groundwoters :
V
= 4370 O00 x
{O3 km3
V = Estimated present amount i A V = Estimnfed rofe of ChQngeS offhe
present mounts during the los+ BO years j T = V:F = overoge turnoverprindj
F = sum of the positive (ornegotive) fluxes. The flux termsofthe scheme ore
given in /O3kma/yeor units
FIGURE1. Principal statistical and dynamic characteristicsof the hydrosphere.
THEEQUILIBRIUM
CONDITIONS OF
THE
GLOBAL
HYDROLOGICAL
SYSTEM
The changes in water level of the world ocean (dH) indicate a residual effect of
input and output in terms of the water balance, which may be summarised by the
following equation:
457
K. Szesztay
where A is surface area,P precipitation,E evaporation,r runoff coefficient (in the case
of polar regions, coefficient of the ice discharge) and the indices “O’:,“L” and ‘‘P”
refer to ocean,land and polar regions respectively. The “most probable” solution of
the above equation for the recent period (the last 80 years) is as follows:
3.3 x 360= 1154 x 360 + 0.39 x 730 x 134+ 0.37 ~ 2 0 x0 16 - 1260 x 360
(14
where data of P, E and d H are given in “/year,
A in 106km2.The value of rLPL is
given according to Lvovitch (1970), the values of Pp and rpPp according to Orvig
(1970) and the value of ØTO according to Budyko (1970). For values of dH,Ao,A L
and A P see Table 1. The value of PO is computed from the equation and agrees very
closely with the value given by Budyko (1970).
For long-term equilibrium conditions of the global hydrological system,the above
equation may be written in a more simple form:
Solving this equation for the equilibrium water surface area of the world ocean:
Data characterising the changes in the equilibrium area of the world ocean
according to variations in the right-hand parameters of equation (3) are summarised in
Table 2.The following conclusions summarise and complete the results:
(a) The equilibrium surface area of the world ocean varies very sensitively with the
water balance conditions of the Globe but reacts to such variations with very long time
lags.The following example may serve as an illustration:
TABLE
2.Variation of the Equilibrium Surface Area of the World Ocean A d according to water
balance conditionsof the Globe.
A surface oreo in I08Xm’ j P precipitation In mm j E
indices :O owan , L land oreas, P polar reyions
rL runoff coefficient i
458
rp cœfflciennf of ice discharyes
evaporation in mm j
The hydrosphere and the h u m a n environment
Let us assume that the runoff coefficient of the land areas will decrease in decades to
come by 0.02 because of increased water uses. Under present climatic conditions a
decrease of ocean area by 18 x 106km2would be the consequence (see the third value
in column 2 of Table 2). According t,othe area-elevation relationship of the world
ocean this decrease in surface area,however, requires a decrease of about 250 m in the
ocean level! This would require - again assuming otherwise unchanged water balance
conditions - at least 40,000years!
(b) The real situation is m u c h more complex than the example above assumes,for
the following reasons:
- The eight parameters of the right-handside of equation (3) are interrelated among
each other and none of them m a y vary without changing several others.
- There are several feed-back effects in the global hydrological cycle. For example,
in the case above, a decrease of the ocean area will also cause a decrease in total
evaporation of the world ocean, and this will slow down the rate of area decrease.
But, owing to decreasing oceanic evaporation, the precipitation will also decrease,
as a secondary feed-back effect, which will d a m p the efficiency of the first
feed-back,and so on.
- The processes of the hydrosphere are deeply interrelated with other geophysical
events, and these interrelations may accelerate and increase the hydrological
influences in certain cases,or may act against the initial process in other cases. The
radiation and heat balance of the Earth’s surface (Budyko 1956) or the kinematic
imbalances of the Earth’s rotation (Hylckama 1970) can be cited as the most
obvious “outside” interrelation of the global hydrological system.
(c) In summary, it can be concluded that the world ocean and the global
hydrological system have no short-term or long-term equilibrium. Their static and
dynamic characteristics(mean ocean level, extent of polar ice caps or the total amount
and distribution of the long-term average precipitation and evaporation) are always
moving with immense inertia and extremely long time-lagstowards newer equilibrium
conditions, conditions which are changing m u c h more rapidly than the processes
themselves and which are governed by a multitude of interrelated feed-back effects
within and outside the hydrosphere.
THEHYDROSPHERE
AND CLIMATIC CHANCES
It is an obvious and well-recognised fact that the atmospheric processes bind the.
hydrosphere into one unique global system. It is less obvious and less well known how
far hydrological processes influence the processes of the global atmospheric system.
First let us look at two simple facts:
(1) About 80% of the total heat balance of the Earth‘s surface is consumed by
evaporation, i.e. by the energy demand of the global water cycle. A 5% change in
long-term global evaporation may cause 20 to 30% or even greater changes in the
other components of heat balance of the Earth’s surface.
(2)The long-term radiation balance of the Earth’s surface itself largely depends on the
hydrological conditions:
(a) In periods when polar ice covers an area two to three times greater than at
present, the albedo of those parts of the Earth’s surface is two to four times
higher because of the difference between the albedos of snow and water and
snow and land (see data in Table 3). Consequently, the total heat retained by
the Globe is considerably (perhaps 5%) less than at present,
459
K.Szesztuy
TABLE
3. Estimated Mean Albedo Values (Budyko,1956).
A.)
Zonal variations
Perenniul snow cover in palor regions {polewords from ‘60)...........O,80
Snow cover of longer durafion in fhe moderute zone (below “60).......O. 70
Snow cover of short duration...................................................... O.43
Coniferous forests.................................................................... O. 14
Deciduous fõrests,proirie areas during humid seasons....................... O. f0
Prairie areos during drought periods, semi-deserts........................ O.30
E.) Effect of surfuce properties
Snow, ice, water
Fresb , dry snow............O.80 - 0.95
Clean, moist snow...........O,60 0 70
Dirty snow...................O.4U - 0.50
Ice on seas and o c e m ......O.30 O 4U
Water surfaces ..............O.05 0.20
Bare soil
Dork soils.....................o.O5 O.15
Mo&‘ ruw soila ............. O.10 O.20
Dry clay or raw sffib.......O.20 - 0.35
Dry Sund soils...............a.25- 0.45
-
-
Agriculfurul areas
Cereals......................... O.IO - O,25
Po fafoes......................... O.15 - O,25
Co f toff............................ o.20 o.25
Mendow.,........................ O,45 O 25
Dry prairies ..................O.20 0.30
Tundra arew .................. O. 15 - O.20
-
Forest areas
-
Coniferous forests ........... D.IO O.45
Deciduous forests ...........O.15 O.20
(b) As the data in Figure 2 indicate,continuous moistening of large areas of desert
by irrigation (or by “exceptional” natural precipitations) may radically
transform the heat balance ofthe soil and increase the total heat retained from
solar radiation by 20 to 30% (Budyko 1956).
The very instability of the processes of the global hydrological system as well as
their deep interrelations and feed-back effects through other geophysical processes
raise the question: are long-term changes in the statistics and dynamics of the
hydrosphere products of climatic changes, or are they perhaps to be considered as
important factors initiating and controlling the climatic changes? An increase in the
extent of snow-covered areas, or moistening of a desert region, may occur as a
“random” event of the natural hydrological regime. But if this event coincides with
other events of the geophysical system which increase the initial effect by
interrelations or by feed-back effects, the residual process may be large enough to
effect climatic changes.
As related discussions at the World Water Balance Symposium indicated (Manabe
and Holloway 1970), computerised models of the global atmospheric and hydrological
systems may considerably clarify these questions, provided the basic data and
relationships of these processes are determined and reflected by the models with a
sufficient degree of accuracy.
460
The hydrosphere and the human environment
Radiutian ba/arrce
.-
L Turbulerrf bed exchange with fbe atmosphere
91
B
.tFu
Heaf storage
of evaporation
evaDoration
Heaf of
lu
5-
a
a
6
12
18
24 hours
-
-----
Irrigated areos
Neignbouring deserf areos
FIGURE
2.Pahta-AralDesert Area,July 1952.
WATER AND THE
BIOSPHERE
Water is the birth-place of life and of the biosphere. It is one of the basic components
of the ecosystems,and also plays an important role as an element interconnecting the
different ecosystems through the processes of the hydrological cycle.
The total amount of the biomass of the land surface is about 3,000to 10,000
thousand million tons,and more than 99% of this amount is represented by vegetation
cover (UNESCO 1970,p.18). A high percentage of this total weight (70% to 90%)
consists of water, but the total amount of water stored in the biomass (about
5,000km3) is a negligible part of global freshwater resources (about 0.015%). It is,
however, a highly dynamic part. Total transpiration of the vegetation cover is about
40,000km3 per year,i.e.its water storage is renewed about eight times a year on the
average (certainly with great variability according to plant type,growing periods and
weather conditions). Human beings and domestic animals consume water to the extent
of about 1O times their weight in a year,i.e. with a water renewal period close to that
of the vegetation.
The areal distribution of freshwaterresources is far from being favourable from the
aspect of high biological productivity. More than 99% of it is concentrated in regions
of low productivity (polar ice caps, glaciers, deep aquifers) and water is partly or
entirely missing in large areas where temperature, sunshine and other components are
favourable (deserts and semi-desertsof the arid zone).
46 1
K.Szesztuy
M A NAND THE HYDROSPHERE
M a n needs water for drinking and for many other purposes. Water is also a decisive
factor in determining the quality of the human environment.
Water Available at Present a n d in the Year 2000
Table 4 summarises global values of estimated water needs and water resources for the
present .time and expectations for A.D.2000 (Lvovitsh 1969). Because of sharp
discrepancies in areal and time distributions of the resources and the needs, a
long-term global balance m a y serve, of course, only as a rough indication. The data in
Table 5 may characterise how far water availability may differ even within relatively
small areas.
TABLE
4.Estimated Global Water Needs and Water Resources (after Lvovitsh, 1969).
1
4965
~
ZDDO
Vifhdrowal Return Wifhdrowo1 Refurn
in CU. irm/yeor
Needs .Municipal water supply
Irrigation
Indusfry
Energy
se
56
2 300
200
250
2840
600
160
235
1051
950
4 250
3 000
4 500
12 700
760
400
2400
4 230
7790
Resources :CU.ktn/year
108 ooa
Precipifution on confinenfs
Runoff
37 o00
regulaied flow
E vopofrnnspirafion
Evapoffonspirotion from agriculfuml or¿?&
BUSEflOW
+
(
15 000)
7/ ooa
(3560)
35 700
(
23 500
72300
(6750)
In spite of the many difficulties and uncertainties in interpreting and estimating
present and future water balances, the following conclusions m a y be drawn from the
above two tables:
(1) The return of used and polluted water into the river systems of the continents
to the extent of about .IO00cubic kilometres per year at present and approximately
10 times more in A.D.2000is a more serious and urgent problem than the availability
of water for withdrawals. A dilution of 1 to 5 or 1 to 10 (in some cases much more) is
necessary for preserving acceptable water quality even if the waters used are more or
less treated before returning them to the rivers or lakes,
462
The hydrosphere and the human environment
TABLE
5. Water Availability Indices of Balcerski in the European Countries based on data of the
1964-1966 survey of the Economic Commission for Europe as published in ECE/WATER
UTIL/METH13/Corr. 1.
CI = RI 2 U
cz = ( R f + R 2 ): U
runoff from the country urea
R2 : Annual runoff originating outside und flowing through the country urea
U : Total annual water consumption (withdrawal)
R,
: Annual
463
7
K.Szesztay
TABLE
6. Water Availability Categoriesfor large-scale regional characterizations(Balcerski,1963).
(R = r P
averuge riverflow (dynamocolwafer msourees)
of the given area
overage onnual precipifofion
average value of the runoff coefficient
total water uses (
wifhdrowu/s) within the
given orea
-
-i-
ategory
Wafer avoifubilify
A
Possibilifies for covering wafer needs are
favourable. Interference for increasing
nofural wafer resources is required on& ut
places with particular& concenfrafed
requiremenfs.
8
Posaibilifies of wafer supply ore in general
ampfable. The number of districts with
temporary wofer shodage is increasing. The
preparation of regional water plans (including
several districts) may become necessarg.
C
Woter resources are inodequote.Comprehensive
planning and consideroble investments ore required
for solving wafer problems.
D
Wafer is a limiting focfor of the economic
developmenf.
(2) Analysing the ratio c of river flow to water uses for different countries Prof.
Balcerski arrived, at a water resources symposium held in Warsaw, at the classification
described in Table 6 (Kertai 1963).
Using the results of the ECE survey given earlier (Table 5), European countries
show the following distribution according to the categories of Table 6 (if river flow
from own territories is considered):
464
,
c >20
10 <c
< 20
5 < c < 10
;
I
I
j
I
: Albania,Austria,Finland,Ireland,Iceland,Norway,Sweden,
Yugoslavia.
: Belgium, Denmark, Italy, Rumania, Spain, Switzerland, Turkey
(European part), United Kingdom,USSR (European pari).
: Czechoslovakia, France, West Germany, Greece, Luxembourg,
The Netherlands,Poland,Portugal.
c < 5
: Bulgaria,Cyprus,East Germany,Hungary,Malta.
The ratio c, or similar simple indices,do not include many important features of water
availability,and apply only to a gross evaluation of the general situation,They show,
however, that if the rate of water use all over the world attained a level corresponding
to that of Table 4,the Globe as a whole would belong in A.D.2000to the category
“Water is the Limiting factor of the economic development”.
(3) The great differences in water-availability indices of European countries, as
determined on the basis of river flow of local origin and by consideration of
“transient” river flow originating from areas abroad,indicate the importance of an
integrated development of water resources in large international river basins, and the
need for formulation and codificationof relevant chaptersof internationalwater laws.
(4)It would be very difficult to answer the question:how shall we keep water use
during the centuriesto come within the limits dictated by the availability of water? We
can conclude, however, from the data in Table 4 that radical changes will be
introduced into national and international water policies during the next few decades.
Several of the expected measures belong to the field of economics and will be
focused probably on the introduction of a well-differentiated price system and
pollution charges,corresponding to real value movements between the water economy
and other different economic branches.
Concerning the technical measures which may reasonably be expected, Lvovitsh
(1969) points out the importance of closed industrial water utilisation systems in
which the water supply is based on continuous recirculation of used and properly
treated water, and in which fresh water is drawn in only to cover unavoidable losses.
Among the less conventional technological approaches, a controlled-environment
agriculture based on deasalination and multiple use of energies and byproducts in a
technically advanced production system (Figure 3) may deserve particular attention
(University of Arizona 1967).
Effect of Man on the Hydrological Cycle
The “Resources” items in Table 4 represent estimates of man-caused changes in the
average water balance of land areas. A slight increase of annual evapotranspiration
(from 71,000k m 3 to 72,300km3 during the 1965-2000period), and a corresponding
decrease in total runoff due to both agricultural development and increase of water
surfaces by man-made lakes, is based on the questionable assumption that average
precipitation over the land areas will remain unchanged. The greatest and most likely
effect of agricultural developmenfs and increased water storage is a great increase in
base flow and regulated flow (from 15,000km3 to 23,500km3)and corresponding
decrease in flood runoff.
Earlier illustrations of the very real instability of the global hydrological system
may indicate how far-reaching will be the consequences that may accompany and
follow the above small changes in the water balance conditions of the land areas.
465
K.Szesztay
If a smaller area is considered, the hydrological effects of man-caused changes
become more rapid and more obvious. Urbanisation may be mentioned as a typical
example of radical alteration in the quantity and quality regime of the local water
cycle as a “lateral” effect of economic development. There are many instances when
changes in the hydrological regime are the basic aims of human intervention (sealing of
the soil surface for water harvesting,modifications in forest management practices for
controlling snow accumulation and snowmelt,etc.)
-
CONTROLLED ENVIRONMENT COMMUNITY
FIGURE 3. Controlled-environmentcommunity.
CONCLUSION
It seems appropriate to try to finalise this broad subject with a narrow but
important conclusion focussing the problem on the subject of this symposium - the
results of hydrologicalresearch on experimental and representative basins.
It may be concluded from the previous pages that learning more about the
atmospheric subsystem of the global hydrological cycle is one of the tasks in hand,and
that building a computerised global model for this purpose is one of the reasonable
approaches. Recent experiments indicate that a proper simulation of the hydrological
processes taking place on the land surfaces is one of the key problems of the modelling
(Manabe and Holloway 1970). Co-ordinated research and measurement from the
global network of experimental and representative areas could probably make a great
contribution to an improved solution of the problem.
466
Tlze hydrosphere and the human environment
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-
467