Future Vulnerability of the Great Plains Region to Drought

The Great Plains-Shortgrass Prairie covers some 320 thousand square miles that ecologically belong to the Steppe Division of the Dry Domain. It has a semiarid continental climate regime with annual precipitation ranging from 10 to 25 inches, and evaporation usually exceeding precipitation. Droughts are unavoidable occurrences throughout the area and even in "normal" rainfall years, ground water overdrafts, mainly for irrigation purposes, are staggering. In 1975 withdrawals resulted in overdrafts to about 63% in the Arkansas-White-Red region, and 25% in the Missouri region. During the same year irrigation consumptive use of water in these two regions was more than 21 billion gallons a day; that represented one-fourth of the country's irrigation water consumption. Irrigated and dryl and cotton, wheat, corn, soybeans and sorghum are grown in the Great Plains. The land that overlies the Ogallala Aquifer, one of the main water resources of the region, is about one hundred thousand square miles. The irrigated crop production in this six-state area represents a total of more than two billion dollars per year in cash receipts, and the value of the livestock industry is more than ten billion dollars per year. Irrigated feed grain production is of primary importance in support of a healthy and growing cattle industry. There has been a net conversion of cropland to grassland between 1967-75 in the Great Plains, but 15 million acres of range and pasture lands went into dry and irrigated cropland. Grass and range lands in these ten states have generally improved due to better management, and in some areas soil erosion has decreased, water supplies have increased due to conservation measures, production and wildlife habitat has increased, and the impacts of extreme weather events have decreased, compared to 1930s conditions.