Method for estimating historical irrigation requirements from ground water in the High Plains in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming

Historical information on ground-water pumpage for irrigation is required for use with a computer model of the High Plains aquifer. Available historical data on ground-water pumpage in the High Plains were inadequate for use with the computer model. Consequently, a method was developed to estimate historical pumpage data.

Two principal components were used to develop estimates of ground-water pumpage: (1) Acreage irrigated; and (2) irrigation demand. The Blaney-Criddle formula was used to calculate consumptive-use requirements for irrigated crops grown on the High Plains. The irrigation demand for each crop was estimated by subtracting precipitation available to the crop from the consumptive-use requirement of the crop. Irrigation demands were combined with irrigated acreages to estimate the volume of irrigation water required for areas in the High Plains. Estimates of irrigation water requirements were compiled for 1949, 1954, 1959, 1964, 1969, 1974, and 1978. Irrigation pumpage for use with the computer model can be estimated from the irrigation water requirements by applying a factor to account for irrigation system efficiency.