Instructions and Tables for Computing Potential Evapotranspiration and the Water Balance
Date
1957
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Abstract
The term water balance has recently gained widespread popularity among climatologists, geographers, geologists, hydrologists, and others concerned with water problems. It has, of course, taken on a variety of meanings depending on the user. In this publication, the term water balance refers to the balance between the income of water from precipitation and the outflow of water by evapotranspiration. It is a climatic balance since the quantities of precipitation and evapotranspiration are active factors of climate. From a comparison of the seasonal march of precipitation with the evapotranspiration, the magnitude of other related moisture parameters, the water surplus, water deficit, soil moisture storage, and water runoff may be determined.
The climatic water balance was introduced into the literature by Thornthwaite in 1944 (Trans. A.G.U., Vol. 26, Part V, pp. 683-693) and used by him as the basis for a new and improved classification of climates in 1948 (Geogr. Rev., Vol. 38, No. 1, pp. 55-94). Since that time, further studies of the water balance by the staff of the Laboratory of Climatology have led to revisions and extensions of the balance itself and its applications. These have been summed up in a publication by Thornthwaite and Mather in 1955 ("The Water Balance," Publications in Climatology, Laboratory of Climatology, Vol. VIII, No. 1, 104 pp.). The approach has been utilized in the following detailed studies of water problems which have appeared in previous issues of Publications in Climatology of the Laboratory of Climatology:
D. B. Carter, "The Water Balance of the Lake Maracaibo Basin During 1946-53," Vol. VIII, No. 3, pp. 205-227.
T. E. A. van Hylckama, "The Water Balance of the Earth," Vol. IX, No. 2, pp. 53-117.
D. B. Carter, "The Water Balance of the Mediterranean and Black Seas," Vol. IX, No. 3, pp. 119-174.
In developing the methods of analysis of the water balance which are used in the Laboratory of Climatology, it has been necessary to produce a number of tables to facilitate the performance of the various computations. Since these methods are being employed widely throughout the world, the present volume has been prepared to give detailed instructions and to provide the necessary tables.