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  • World Water Balunce

    World water balance (General report)

    Professor M. I. Lvovitch, Institute of Geography of the AS of the USSR, Moscow

    RESUME : Cette communicatjon expose la notion de bilan hydrique mondial en gnral, ainsi que l'importance qu'elle revt notamment pour accrotre notre connaissance des processus hydrolo- giques et pour valuer les ressources en eau du globe terrestre. Elle contient un historique des diffrentes valuations faites par plusieurs chercheurs pour diverses parties du cycle hydrologique, ainsi que des tables correspondantes. L'auteur a procd i une tude critique dcs diverses mthodes utilises pour arriver ces valuations, dgageant ainsi les lments pour lesquels il y a lieu de poursuivre les recherches.

    BILAN HYDRIQUE MONDIAL (RAPPORT GENERAL) SUMMARY: The paper presents the concept of world water balance in general and its importance, in particular for the advancement of knowledge of hydrological processes occurring on the earth and for estimating world water resources. A historical review of various estimates made by different scientists for difcrent parts of the hydrological cycle is given with relevant tables. The author has made a critical study of various methods used for such estimates thus separating those elements which need further research.

    BALANCE HIDROL~CICO MUNDIAL (tlljurtne generai), RESUMEN: En este documento se presenta el concepto del balance hidrolgico mundial en generai y, en especial, su importancia para el progreso del conocimiento de los procesos hidrolgicos que se producen en la tierra, as como para calcular los recursos hidrulicos mundialcs. En las tablas correspondientes se hace un examen retrospectivo de las diversas estimaciones efectuadas por diversos cientficos para diferentes partes del ciclo hidrolgico. EI autor ha realizado un estudio crtico de los diversos mtodos utilizados para estos cilculos, separando, por lo tanto, aquellos elementos quc necesitan de ulterior investigacin.

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  • M. I. Li~ooitcli

    GENERAL QUESTIONS

    World luafel- balance should be considered as a quantitative expression of a great process called the iouler cycle which takes place on the earth. The two ternis characterize different sides of the same process. That is why the differentiation in the two concepts which some investigators resort to cannot be considered well grounded. In the past, the hydrological science was limited by qualitative notions of water cycle but when, due to the progress in water resources use, the hydrometric and atmospheric precipitation data became availa- ble, it became possible to comprehend this process qualitatively. Water cycle, as it is known, connects together all parts of the hydrosphere: ocean and

    water on land, i.e. surface, soil and ground waters; as well as water in other components of nature, e.g. climate, soils, geological structure and biosphere. In the process of water cycle erosion occurs; relief is formed; dissolved matters change place; large quantities of heat are transferred and a most important biological process-transpiration-occurs. One of the links in the water cycle is the important economic link wherein water is

    used to meet mans needs. The term ioater balance cannot be considered literally as balancing, i.e. equality

    between income and output elements of water balance. Jt is obvious that in the studying of water balance, it is indispensable to observe the law of matter conservation. The water cycle for the whole world is not watertight and, therefore, a perfect balance is not possible, either on a global basis or on a regional basis. The study of world water balance, as a whole as well as separate continents and oceans,

    depends on the state of knowledge of two major water balance elements-precipitation and river runoff. It cannot be said that present knowledge of these elements is quite perfect, Nevertheless, available data, even if insufficient, together with scientific theory make it possible to solve a whole set of water balance problems as well as to estimate world water balance, provided suitable methods for investigating are applied. The importance of studying world water balance lies in the fact that the development of

    knowledge of any processes occurring on the earth, including the water cycle, is a contri- bution to general scientific and ecmcmic progress. It plays an important part in estimating the world water resources, which are continuously being used within the process of water cycle. The level of our knowledge on the water cycle and world water balance also indicated the level of our understanding of world water resources and, in this way, partly suggests the right ways of their use.

    DEVELOPMENT OF THE COMPREHENSION OF WORLD WATER B AL AN CE^

    Already in accient times, a certain ncticn of water cycle existed in a very crude form which was far frcm reality. A better qualitative picture of water cycle appeared during the Renaissance (Leonardo da Vinci) period. Significant contributions to promote such knowledgp, was made in the XVII-XVIIIth centuries by persons like P. Perrault, M.V. Lomonosov, Lh. Buffon, P.I. Ritchkov, J.Dalton and others. But a lack of information n tfe fcrm c discerned data made their contributions less effective. The present estimations of world water balance were initiated by E.Ya. Brikner of

    USSR (1905). The method of estimating world water balance suggested by him has

    I. The Rusiaii terni umler circiilrrtio/z ~orrcsponds to the Anglo-American term miter cycle

    2. The section is prcpared in collaboration with Prof. A A . Sokolov, Statc Hydrological Institutc. or *h.vdrnlu,yicul c.vc.Ie.

    USSR.

    402

  • World Wciter Boltitice

    probably a greater importance than Lhe actual estimate of balance. The essence of the nxthod lies in the following equations:

    - For the peripheral part of the land feeding the Ocean with stream water: E,, = P,, - R,; - for closed areas without runoff to the Ocean: Eo = P,; - for the Ocean: E,,, = P,,, + R,,; - for the Earth: E = E, +E,,, ; where: E,, evaporation frem the peripheral part of the land; P, precipitation on the peripheral part of the land: R, river runoff to the Ocean; E, and P, evaporation aiid precipitation of closed areas and E,,, and P,,, E E,

    evaporation and precipitation of the Ocean; evaporation from the surface of the land; evaporation from the whole of the land.

    The next step was made by R. Fritzsche (1906), who was the first to obtain values of river runoff close to the present ones. G. Wst (1920), improved upon it by adding runoff from Polar glaciers to river runoff. Both results of G. Wusts estimation (1920 and 1936) of the world water balance are characterized by low values of precipitation and evapora- tion of the Ocean. Attention was drawn to this by W. Meinardus (1934) who probably prepared the first reliable map of atmospheric precipitation for the Ocean.

    TABLE 1. World Water Balance from the data of different authors (cm)

    Author, year Precipitation Evaporation Total river - runoff from

    Land Ocean Total Land Ocean Total land

    E. Brikner (1005) R. Frizchc 11906) G. Wst (I 920) W. Meinardus ( 1934) G. Wust (1936) M.I. Lvovitch (1945) M.I. Lvovitch (1964) M.I. Budiko (1956) F. Albrecht (1961) R. Nace (1968) M. 1. Lvovitch (1969)

    85 15 75.2 67 66.4 12 13 10

    61 73.5

    98 94 61.3 98 91 54.5 74 74.3 50.7 114 100.2 42 82.3 11.1 41.6 114 101.5 41.6 114 107 48.7 1C2.4 92.8 44.6 104.6 88.5 82.5 41.0 113.1 1C2.0 48.5

    I05 1 o5 84.3 124.2 92.5 I24 I24 112.7 114.4 91 124.0

    94 91 74.3 100.2 17.7 101.5 107.0 92.8

    82.5 IG2.0

    17 20.5 24.9 25 24.8 24.4 24.9 25.4 22.4 28.5 25.0

    A principal distinction of our world water balance investigations lies in the fact that they are based on the first map of world river runoff (Lvovitch, 1954) and on the fairly detailed map of precipitation on the land, prepared by O.A. Drosdov in 1939. M y subsequent world water balance estimations are based on making river runoff maps (fig. i) and data for the runoff of Polar glaciers more accurate. M. I. Budiko (1965) and later F. Albrecht (1961) in their research estimated evaporation

    from heat balance, and river runoff fro in the difference between precipitation and evaporation. Attcntion is drawn to the fact that world water balance elements have not substantially

    403

  • M. I. Luouitch

    changed throughout thc history of research in this field. This shows a great insight of our predecessors in solving the problem on the basis of very poor information. The results of the various estimations of separate water balance elements are basically

    dependent on the accuracy of estimation for precipitation, especially in the Ocean. Thus, beginning from W . Meinardus (1934) precipitation on the Ocean area, (excluding G. Wst's estimation) is assumed to be more than 100 cm. Precipitation on the surface of the Ocean should be assumed not less than I14 c m provided corrections for gage records are applied. The methods of correction have been developed by the Iiydrometeorological Service of USSR (M. J. Budiko's paper for the present Symposium). River-runoff value, as indicated above, has remained almost unchanged for the past

    fifty years. This does not imply the lack of progress in the study of this world water balance element. For instance, runoff data obtained from the first map of world river-runoff (1945) differ from the results of Fritzsche Wst's calculations (1906, 1920) for selected 10"- latitude zones by 90% to 116%. For the world, as a whole, the results of both calculations have agreed. Here the law of great numbers reveals itself, i.e. compensation for errors for large areas. However, the understanding of river-runoff distribution over the area has substantially improved. The same is true of the runoff from Polar glaciers into the Ocean. According to the data

    of different authors an annual runoff from Antarctica and Greenland is estimated as follows (table 2). The splendid results of international research of Antarctica for the past one and a half

    decades are reflected in the table. Without claiming a full survey of world water balance estimations we must mention the investigations of A.A. Kaminskiy 1925), W. Halbfass (1934), A.B. Voznesenskiy (1938) and others on this problem.

    TABLE 2. Runoff from Polar glaciers into the Ocean (km3)

    Source Antarctica Greenland Total

    G. wst (1920 3 500 W. Meinardus (1934) 640 M.I. Lvovitch (1945, 1964) 1100 P.A. Shumskiy, (1965) ArN. Krenke V.M. Kotlyakov (1969- 2 200 (paper for the present symposium)

    1 O00

    600 -

    600

    4 500

    1700 -

    2 800

    The details of the last estimate of world water balance made by the author are shown in table 3. In the last estimation a series of questions remains still unsolved. The inflow of ground-

    water directly into the Ocean bypassing rivers is not yet known. R. Nace estimates this value at 5%) of the runoff of world rivers, i.e. at 1 600 km3. I believe that this value does not appear to be overestimated, and R. Nace himself considers it to be fairly approximate. The necessity of searching for ways of detcrniining the inflow of groundwater into the Ocean is, therefore, a mutual desire. Thc characteristic river-runoff from selected parts of the land is shown by the data of

    table 4. In terms of depth of runoff South America has a world lead, Europe occupies the second

    place and next are Asia, Africa and Australia in descending order.

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  • World Water Balance

    TABLE 3. World Water Balance

    Water balances elements Volume km Depth mm

    Peripheral part of the land Precipitation River-runoff Evaporation

    Precipitation Evaporation

    Precipitation River water inflow Evaporation

    Precipitation Evaporation

    Closed (inland drainagc) part of the land

    World Ocean

    The Earth

    IO2 100 37 400 64 700

    7 400 7 400

    410 500 37 400 441 900

    520 O00 520 O00

    813 320 553

    23 1 23 1

    1137 103

    I 240

    1020 1 020

    1. Including the evaporation of 755 km of river-runoff.

    TABLE 4. River-runoff by parts of the world

    Parts of thc world Volume of annual runoff Depth m m km

    1 2 3

    Europe 2 950 Asia i2 850 Africa 4 220 North America (together with Central America) 5 400 South America ; 8 O00 Australia (with Tasmania, New Guinea and New Zealand) 1920

    Antarctica and Greenland 2 800

    3 O0 286 139 265 44 5

    21 8 164

    The total land Including inner (drainlcss) areas lncluding peripheral parts of the land

    38 150 750

    37 400

    252 23 320

    1. M a d e from more accuratc data of 1969 2. Without new (1964) American-Brazilian data on the Amazon runoli

    PERSPECTIVES OF WORLD WATER BALANCE RESEARCH

    To outline the perspectives of world water balance research it is wise to turn again to a historical review. The great importance of the water balance equation for river basins, P = R+E (precipitation is equal to runoff plus evaporation), in the development of hydrological science is well-known. This equation appears in our literature as Penck- Oppokovs equation. The prominent Australian scientist A. Penck who is better known as a geomorphologist has made an appreciable contribution to the development of hydrol- ogy, especially to the development of water balance study (Penck, 1896). The other distinguished Russian hydrologist E. V. Oppokov who is the author of well-known

    405

  • 106

  • M. I. Lwuitclr

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  • M. f. Luouitch

    papers on the Dnieper River hydrology (1904, 1914), has carried out a series of interesting theoretical investigations on hydrology and in particular he has pointed out the difference between water balance equations for short and long periods of time.

    It should be noted thal the well-known investigator on water balance, R. Keller, considers that E.Ya. Brikner of USSR was the first to suggest the above-mentioned formula in 1887, i.e. nine years prior to A. Pencks publication (R. Keller, Russian edition, page 270). That is why justice would demand the major formula of water balance to be named Brikner-Oppokovs equation. In any case, this formula has made a whole epoch in the development of hydrological

    science. With it are linked great methodologic studies of such well-known scientists as: E.A. Brikner (1887), A. Penck (1896), E.A. Geints (1898), E.V. Oppokov (1900, 1904), W . Ule (1903), P. Schreiber (1904), Hans Keller (1906), A. Coutagne (1921), V.G, Glushkov (1924, 1961), P.S. Kusin (1934), W. Wundt (1937), M.A. Velikanov (1940). L.K. Davidov (1947), V.A. Troitskiy (1948), M.I. Budiko (1956), Reiner Keller (1962, 1965) and others. Neverthcless, the hydrological science has exhausted the above-mentioned equation

    and many scientists and practical workers have already paid attention to its inadequacy. The essence of the matter lies in the fact that while making use of data on river-runoff as a whole or, as we call it, the total runoff it is impossible to reveal the lithogenous link (groundwater, soil moisture) of the water cycle. That is why alrcady in 1903 while studying the water balance of the Oka River Basin E.A. Geints of USSR took notice of the inadequacy of the water balance equation which does not reveal the groundwater compo- nent of river runoff. In connection with this he approximately estimated the value of groundwater runoff of the Oka River. Later (I 924) V. G. Glushkov suggested a method for determining groundwater feeding of rivers through the separation of hydrographs and found out groundwater runoff into the rivers of Middle Asia. Subsequent to this problem a series of investigations were dedicated by G. N. Visotskiy (19321, A. V. Ogievs- kiy (1932), B. 1. Kudelin (1949) and others. After studying sources of river feeding in the USSR, and in the world and separating hydrographs the author gave a mass estimation of groundwater runoff into rivers. A similar method was used by E. Natterman (1951), G. Schroeder and W. Friedrich (1953) as well as by W. Wundt (1958) in FRG (cited from R. Keller, 1962, 1965). The appearance of the method for determining a groundwater component of river

    runoff gave the practical possibility of solving the following system of different equations of the water balance of an area (author, 1959, 1963):

    R = U + S ; P = U + S + E ; W = P - S = U + E

    R total river runoff; CJ groundwater (stationary) runoff into rivers ; S surface (flood) runoff; P atmospheric precipitation; E evaporation; W total soil inoisture of an area (practically an annual infiltration or an annual renewal

    K. and K, coefficients of groundwater discharge into rivers and of evaporation. of soil moisture storage);

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  • World Wafer Bolance

    The earlier statement that all kinds of water resources in nature are interconnected by the water cycle process has been approximately determined by using the above-mentioned system of equations. The above-given method for studying the water balance of an area is not free from

    some drawbacks which should be noted to obtain best results. It does not take into consideration the whole of the groundwater runoff from the land but only from the part drained by rivers which constitutes the groundwater in the active water-exchange zone. Groundwater, occurring below the level of drainage by river systems has little participation in the water cycle and is often stagnant. Therefore, the methods require careful application when the magnitude of river interbasin feeding with artesian water is great and also in karst areas. Nevertheless, the method mentioned has already been widely used in the USSRlfor

    10 years. The State Hydrological Institute and Jnstitute of Geography of the A. S., USSR, have

    prepared maps of water balance elements for the area of the USSR (Water Resources.. . , 1967; Water Balance. .. , 1969; Lvovitch and Dreier, 1964). Similar investigations have been carried out for the areas of Romania (Monografia..., 1960) and Bulgaria (Geo- graphy of Bulgaria, 1966). At present, at the Institute of Geography of the Academy of Sciences of the USSR

    studies on the water balance of the world continents are being completed with the applica- tion of the new method. Some results of these studies are given in table 5. Groundwater runoff is the most stable part of river riinoff and, as a rule, it does not

    need any control and hence is the most valuable part of water resources. At the same time groundwater runoff into rivers has a character of fluctuating groundwater storage. This element of water balance cannot be estimated by former methods. T o receive a full concept of stable river water resources, runoff controlled by lakes and reservoirs should be added to groundwater runoff. (See the foot-note to table 5). Surface (flood) runoff cannot be utilized for many practical purposes without control-

    lins it with the help of reservoirs. This water-balance element amounts to 33 O00 km3 for the whole land and to somewhat more than 20 O00 km3 excluding ice, snow and water runoff from Polar glaciers. This value may be considered as potential river water resources whereby the increase in the stable runoff and groundwater storage are possible.

    TABLE 5. Watcr balance estimation of water resources for the whole land, Europe and Arica ~ ~

    Waler balance elements The whole land Europe Africa

    k m 3 mm k m 3 mm k m 3 m m

    Precipitation ; P 108400 730 7025 714 20800 683 Total river runoff; R 38 150 260 2950 300 4220 139 Groundwater runoff; U 12 O001 81 1 O002 102 1 4603 48 Surfacc (flood) runoff; ,S 26.150 179 1950 198 2 760 91 Total soil moisture of

    an area; W 82250 551 5075 516 18 040 592 Evaporation; E 70250 470 4075 414 16 580 544

    Coefficients: of groundwater discharge

    into rivers; Ku 0.14 of runoff; K, 0.35

    0.17 0.43

    0.08 0.20

    ~~ ~~ ~ ~~ ~~

    Foot-note: Stablerunofftogsther with the runoffcontrolled by lak% and water rzxrvoics: (a) 15 O33 km ; 8) 1 SOO km3 ; (c) 1 760 km3.

    40 9

  • The new method. for studying watcr balance makes it possible also to approximatcly estimate yearly rcnewed soil moisture which is another water resource, one of thc most important components of soil fertility and a source of the most important process o vital activity of plant-transpiration. For water balance estimalion Europe is given as an example for a part of the world

    well studied hydrologically and Africa for a part of the world not so well studied. While studying waler balance in Africa, sufficient initial hydrometeorological data for

    only 14 countries were available which cover about one third of the area of this continent. The intial hydromeleorological data available on the other 34 countries covering two- thirds of Africa are meagre. Nevertheless, thanks to the method used it has been possible to receive an approximate

    but full picture of the water balance for the whole area of this continent although poorly studied hydrologically. A major feature of the method applied is mapping of water balance elements. This

    method is quite old in Soviet hydrology. Mapping of hydrological regime elements has been widely applied in our country since the 1920s when hydrological science was faced with great practical tasks of first five-year plans of economic construction which were to be solved under conditions of a poor knowledge of our countrys hydrology. But when some time later the area of the USSR had been already well studied hydrologically the necessity of the application of the mapping method remained. No matter how dense the network of hydronieteorological stations is there are always streams and areas for which water balance parameters are to be solved by methods of space interpolation.

    Mapping combined with methods of interpolation is facilitated by using relationships between hydrometeorological elements of water balance for which better information is available. There are good examples of such relationships in papers by H. Keller (1906), E. M. Oldekop (19111, M.A. Velikaiiov (1928), A. Meyer (1928), V. G. Glushkov (1929), B. D. Zaikov (1935). W. Wundt (1937) and in a series of other papers. At present we apply relations between water balance elements differentiating them for different geographical zones (author, 1968, 1969). Such relations for interpolation enable water balance elements and water resources to be approximately estimated under a poor knowledge of hydro- logical conditions. It is impossible to do interpolation for Europe without such relations, at any rate for such mountainous areas as the Alps, Carpathians and others. For them we prepare water balance maps on the basis of regional relations of water balance elements according to the elevation of river basins just as those established for the Caucasus (Zaikov, 1933, 1946), for lhe Aare basin (Spillman, 1936), for Middle Asia (Schultz, 1949, 1965), for the Caucasus (Vladimirov and others 1964), for the Urals, Altai, Middle Asia, Caucasus (Water Balance of the USSR ... , 1969) for Little Caucasus (Rustanlov and others, 1969) etc. It was also impossible to do without dependence on interpolation in filling the blank

    spaces on the map of the world river-runoff (fig. 1).

    WATER EXCHANGE ACTIVITY ON THE EARTH

    Consideration of separate parts of the hydrosphere on a static basis does not give a true picture of the world water resources. Due to the water cycle lhe hydrosphere is in a state of continuous movement and its

    components are continuously being spent and renewed. Thanks to this remarkable rcature that causes a continuous rcnewal of water resources mankind is continuously receiving new masses of fresh water for use. For theory and practice of utilization of water resources it is essential to know the

    410

  • World Water Balcriire

    reiiewal rate of separate parts of hydrosphere or water exchange activity (A), which may be estimated from the following relation:

    w AW

    A =-;

    where: W volume of hydrosphere or its separate parts in km3 ;

    A W a water balance element in kni3 per year, most intensively participating in the

    Then the hydrosphere activity is expressed by the number of years during which a full replacement of the stationary resources of a given part of the hydrosphere occurs. The above-mentioned index, as applied to mans organism, consists of time during

    which the total blood of the organism passes through the heart. This process requires one minute in a state of rest. This activity of blood circulation is similar to water exchange activity. For example, with a volume of the World Ocean of 1 370 million km3 and an annual

    evaporation from the Ocean of 448 O00 km3 the water exchange activity in this major part of the hydrosphere approximates 3 O00 years. Another example with a simultaneous volume of river channel water of 1 200 k m 3 (author, 1945) and an annual runoff of world rivers of 38 160 km3 the water exchange activity takes 0.032 years (table 6). Consequently, the replacement of the whole volume of river channel water occurs 32 times over a year of approximately over 11.4 days. River waters feature a very high note of exchange activity and there are many advantages in this. O n the other hand difficulties are encountered when the water exchange is very active, in which case more efforts are required to be made for water stabilization by controlling river-runoff. From this stand- point the characteristic water exchange activity index of World river waters along with the drained lakes constitutes about 1 O years.

    balance of a given part of the hydrosphere.

    TABLE 6. Water exchange activity of the hydrosphere and its separatc parts

    Parts of hydrosphere Stationary volume Water exchange activity of water thousand km3 (the numbcr oyears)

    World Ocean The total groundwater Including the zone of an active Waterexchange Glaciers Lakes Soil moisture River (channel) waters Atmospheric vapour

    The wholc hydrosphcre

    1370000 60 O00 4 O00 24 000 230 82 1.2 14

    3 o00 5 000 330

    8 600 10 1

    0.032 0.027

    I 454 327 2 800

    The water exchange rate of the Polar glaciers is extremely low. Its volume according to the recent data considering sub-ice relief of Antarctica is reduced almost by 5 O00 O00 km3 and makes up 24 O00 O00 km3 (Shumskiy and Krenke, 1965). In connection with this the water exchange activity rate of the Polar glaciers must be estimated approximately at 8 600 years which points to an exclusively slow charactei. of exchange processes in this part of the hydrosphere. The exchange activity of groundwater is estimated very approxi-

    41 1

  • M. i. Lvooiich

    mately since reliable data on the volume of free groundwater in the earths crust are not available .V.I. Vernadski y (I 933) estimatcs approximately free waters, i.e. thosc which are not physically or chemically related to minerals, at 60 O00 O00 km3, which. was later proved by F.A. Makerenkos studies (1966). Bearing in mind that an annual volume of groundwater feeding rivers constitutes 12 O00 km3 the exchange activity time of the total groundwaters is estimated approximately at 5 O00 year. It is also indicative of an extremely slow rate of exchange of groundwaters because of the presence of depth brines the age of which is proportionate to the rocks containing them. For the groundwaters of the active waler exchange zone we have made use of the data

    of R. Nace (1964, 1968) for the groundwater storage in the upper part of the earth crust which is 0.5 miles (0.8 km) thick. The groundwater activity rate of the zone is estimated at one third of a thousand years. Generally, groundwaters as well as glaciers are distin- guished by a great range of rate of exchange from a period of a year in the case of tempo- rary perched water to many thousands of years for deep stagnant groundwaters. Soil moisture exchange occurs in about a year. As for atmospheric vapour, its replacements come about even more rapidly than the

    replacement of river waters: in 0.027 years, i.e. almost every 10 days or 37 times per year. The water exchange activity of the hydrosphere as a whole constitutes 2 800 years.

    It means that the replacement of the whole mass of the hydrosphere through the water cycle takes place every 2 800 years. The hydrospheric replacement process which started in the times of Homer is being completed only now. The above review of the hydrosphere points to a great heterogeneity of its separate

    parts. The prominent feature of fresh ,waters is their high rate of exchange activity. Glaciers are an exception.

    CONCLUSION In thc past six to seven decades hydrological science has achieved interesting results in studies of world water balance. At the same time the progress of science caniio1 be coniined to the attained success. One more stage in studies of world water balance with the help of the new method is

    being accomplished which will reveal the lithogenous link of the water cycle. Eut now a further development of studies in the field should be planned. There is no

    doubt [hat with close collaboration within the frameworlc of the IHD it is feasikle to get more details for the development of world water balance and bring these studies to a higher level of accuracy. With this aim in view some difficult questions must te solved. Cne of the important tasks lies in preparing a map of atmospheric precipitation with

    correction for records of diflerent types of gauges used in different countries. It is essential also to search for a method of estimating groundwater inflow into the Ocean by-passing the rivers. It is needless to say that there is also the task of improving information on water balance elements, especially in soine areas of Africa, Asia and South Ainerica. However, time is needed to fill gaps in hydrometeorological information on water balance elements. Hence limited data available must not be a handicap to a further development in world balance studies. A deficiency in information should be made up by the devclop- ment of the hydrological science, its theory, empirical relations for interpolation between separate water balance elements. Advances in the hydrological science may not be restricted to studying natural water

    balance. One of the major tasks lies in studying water balance transformation caused by mans activity. In this field, much has already been done by science: theory has been developed, the

    naturc and magnitude of water balance transformation in the USSR and. Centrai Europe have been determined. Nevertheless, studies in water balance transformation as wcll as in hydrological rcgiine as a whole continue to be major tasks of science.

    412

  • World Wafer Balriiice

    I1 should, in the end, be noted that there is a trend in the hydrological science to determine principles of water resources utilization and conservation to exclude the possibility of their depletion. An approximate forecast of the state of world water resources and world water balance

    transformation for the year 2000 (author, 1968, 1969) indicates the fact that the use of rivers, lakes and water reservoirs and also seas for sewage discharge is a inajor hazard of water resources depletion. This hazard may be eliminated with the help of a series of expedient measures. W e want to emphasize that the future water crisis is not inevitable. On the basis of

    a forecast which makes it possible to obtain an approximate model of the future state of water resources it becomes clear that water resources depletion may be avoided and if more rational principles of their use and conservation are put into operation then mankind is not threatened by water crisis.

    REFER ENCES BRIKNER, E.A. (1905): Water cycle balance on the Earth, Pocliuouedeiiiye, vol. 7, N 3. BLJDIKO, M. I. (1956): Heat balance of the carth surpace, L. BYUFFON, Zh. (1789): Gciierai and partial history, p. I, S.P.B. DAVIDOV, L.K. (1947): Runoff depth in the rivers of the USSR, its variations and the cffcct of

    DAVIDOV, L.K. (1953): Hydrography of the USSR (waters of the land), L. DROZDOV, O. A. (1959): Moisture cycle and its role in natural processes, L. FEDOSEEV, I.A. (1967): Development of knowledgc of water cycle and its origin and quanlity on

    GEINTS, E. A. (1898): Precipitation, the amount of snow and evaporation in dinerent basins of

    GEINTS, E.A. (1903): The Oka River Basin. The runoff depth in the head reaches of thc Oka in

    GLUSHKOV, V. G. (I 924): Calculation of groundwater feeding in the system of the Zeravslian

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    A study of the atmospheric heat aiid moisture budget between Equator and 60 ON during the winter and summer seasons

    Stefan Hastenrath, The University of Wisconsin

    SUMMARY: On the basis of seasonal mean data, the divergence of the flux of latent heat, potential ciicrgy and sensible hcat is computed for the layer 1000-100 m b and 100 latitude belts between Equator and 60"N. The magiiitudc of latitudc-mean evapotranspiration resulting from the latent heat budget is realistic. Similarly, the budget of sensible heat and potential energy for the entire

    41 5

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