ALBERT

Notizen: Modifications in the computed climatic water budget have made it possible to achieve good agreement between computed and measured stream flow on both a monthly and annual basis in basins without appreciable winter snow cover. Comparisons of computed and measured stream flow in 28 basins on the Delmarva peninsula show that for some basins the agreement is excellent (regression line essentially equals unity), for other basins the regression line has a slope of one but it is displaced above or below the y=x line, while for other basins, the slope of the regression line differs appreciably from unity. Study of the basins where agreement between computed and measured values is only fair to poor reveals that the patterns of disagreement can be used to provide information on the water holding capacity in the root zone of the soil, on the quantity of deep aquifer recharge within the basin, or on the effect of human modifications within the basin. The technique should also reveal the quantity of interbasin transfers or other consumptive uses within the basin. The water budget, thus, becomes a useful tool to study hydrologic characteristics or their changes over time within a basin.

Notizen: Abstract About twenty geographers from the Soviet Union and the United States of America T. V. Bochkareva, A. V. Drozdov, N. F. Glazovsky, S. P. Gorshkov, A. N. Krenke, S. M. Myagkov, V. N. Solntsev, A. A. Velitchko from the USSR; R. G. Barry, S. N. Goward, D. Greenland, J. A. Jones, J. K. Mitchell, W. E. Riebsame, T. Webb, and C. J. Willmott from the USA. have joined in a review of selected geographical approaches to the study of global change. Taking account of the new effort sponsored by the International Council of Scientific Unions under its International Geosphere-Biosphere Programme to investigate major alterations in the world environment, they examine relevant geographical experience. Rather than assembling a collection of papers by individual authors, the project encouraged the preparation of a joint set of findings and observations.

Notizen: Summary A knowledge of the moisture balance at the earth's surface is essential to an understanding of climate. Precipitation and its areal distribution have been investigated in much detail. Evapotranspiration, which is the reverse of precipitation and represents the combined evaporation from the soil surface and transpiration from plants, is little understood and seldom measured. Actual evapotranspiration depends on climatic factors but is limited by the amount of available moisture in the soil. On the other hand, potential evapotranspiration which may be defined as the amount of water which would be lost from a surface completely covered with vegetation if there is sufficient water in the soil at all times for the use of the vegetation depends on climate alone. In order to evaluate the moisture factor in climate, the moisture supply or the precipitation must be compared with the water need or the potential evapotranspiration. The distribution of precipitation through the year never coincides with, and seldom parallels, the distribution of potential evapotranspiration. When the precipitation is in excess of need, the surplus goes to recharge ground water and produce runoff. When the precipitation does not equal the need, there is a deficiency which results in drought. There are various methods of measuring evapotranspiration, all of which are subject to many limitations, and only two of which give promise of yielding acceptable results. The first of these, the so called “vapor transfer” method, is of especial interest because it is the only one in which measurements may be made of a natural surface without disturbing it in any way. It is not yet a practical method because it requires greater precision in instrumentation than is feasible at present. The second, utilizing a soil tank or evapotranspirometer, is more artificial but it can provide reasonable results if used with care. The evapotranspirometer consists of a sunken open topped tank filled to ground level with soil on which vegetation is planted. A permanent water table is maintained in the soil at a given depth. A large area surrounding the tank must have a vegetation cover the same as in the tank. In addition, soil moisture both inside and outside the tanks must be maintained at the same level. The evapotranspirometer has proven to be a useful and inexpensive instrument for measuring potential evapotranspiration. Soil tank evapotranspirometers have been installed in thirteen localities during the last few years. Pending further theoretical work on the problem of evapotranspiration and the accumulation of observations an empirical formula was devised from data of irrigation projects and watersheds to give the potential evapotranspiration from climatological data alone. The formula has been applied with considerable success by investigators in various parts of the world. The relation between potential evapotranspiration and precipitation at nine European stations is discussed (see fig. 6). Potential evapotranspiration follows a uniform pattern through the year in most of Europe. It is negligible in the winter months as far south as central France, northern Italy, and southern Russia and reaches only 3 cm a month in southern Spain. It rises to a maximum in July that ranges from 10 cm in northern Scandinavia to 17 cm in southern Europe. Precipitation, on the other hand, is highly variable from one region to another. In southeastern Europe it is low, resulting in a large summer water deficiency (56.9 cm at Athens, Greece). This deficiency exists in the summertime over most of the rest of Europe, with the exception of certain restricted regions such as around Zurich, Switzerland. Over western Europe where the precipitation is greater and more uniform through the year the summer water deficiency is smaller. It is 10.6 cm at Birmingham, England and only 2.1 cm at Vard, Norway. In times of excess rainfall water is stored in the soil. The part of this water that is within reach of roots is used before the plants begin to suffer. From studies in western United States it was found that under ordinary circumstances the amount of water stored in the root zone that is available to plants is equivalent to 10 cm of rainfall. The uses as well as the limitations of potential evapotranspiration are only partially known. Even with its present limited use in climatology, hydrology, agriculture, and soil tractionability, it has shown itself to be a powerful tool. With more information concerning the nature of potential evapotranspiration and knowledge of its areal distribution from the tropics to the arctic, its usefulness should increase manifold.