The time and space distributions of the abiotic driving forces are the topics of consideration of this paper. The climate as defined by solar radiation, temperature, precipitation, evaporation, runoff, and wind is discussed. The distribution of these quantities across the grassland of the United States is shown by a series of maps developed from the long-term climatic records. Discussion of these parameters is focused on the factors that delineate the boundaries of the grassland and variations within the grassland area. A simple energy and water balance of the earth-atmosphere interface is described (Thornthwaite-Mather model), and the model is applied to the mean monthly data at each of seven IBP Grassland Biome intensive observation plots. Characteristic soil moisture variations for each site are computed, and intersite comparisons are made. An identical analysis is performed for the 1970 data at each site. Variations in 1970 soil moisture between sites as well as deviations from the long-term average are noted.