World food production depends to an important degree upon the availability of water for crop production. Crop production is principally a function of soil water availability, soil fertility and (within an optimum range) available energy. Either deficits or excesses of any of these factors result in reduced yields. The World Meteorological Organization, WMO has published a summary of available worldwide climatic data for the 30 year period 1931-1960. This data summary provides a convenient basis for evaluating water deficits and excesses and for determining available energy for a large number of locations.