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Ground-water recharge and consumptive irrigation requirements (CIR) in the Great Plains and adjacent areas largely depend on an environment extrinsic to the ground-water system. This extrinsic environment, which includes climate, soils, and vegetation, determines the water demands of evapotranspiration, the availability of soil water to meet these demands, and the quantity of soil water remaining after these demands are met for potential ground-water recharge.The geographic extent of the Great Plains contributes to large regional differences among all elements composing the extrinsic environment, particularly the climatic factors. Mean annual potential evapotranspiration ranges from about 26 inches in northeastern North Dakota to about 68 inches in eastern New Mexico. Mean annual precipitation ranges from about 10 inches in northcentral Montana to about 48 inches in central Arkansas. Cool-season precipitation, the seasonal precipitation most critical to recharge, is even more regionally variable and ranges from about 2 inches in northeastern Montana to about 23 inches in Arkansas. Variability of soils and vegetation tends to modify local soil-water balances.A soil-water simulation program, SWASP, which synthesizes selected climatic, soil, and vegetation factors, was used to simulate regional Deceased.

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Regional variability in water-level change in the High Plains aquifer underlying parts of Colorado,