Major Aquifers and Groundwater Depletion

Groundwater held in aquifers supplies drinking water and irrigation for a substantial share of the world's population, and a handful of exceptionally large aquifer systems illustrate both its scale and its vulnerability. The Ogallala Aquifer, also called the High Plains Aquifer, underlies portions of eight U.S. states from South Dakota to Texas, covers roughly 450,000 square kilometers, and supports an estimated 30% of all irrigated agricultural land in the United States, chiefly the region's corn, wheat, and cattle-feed operations. Since large-scale center-pivot irrigation pumping began in the mid-twentieth century, water tables in its southern reaches, particularly in the Texas Panhandle and western Kansas, have dropped by dozens of meters in places, and because the aquifer's natural recharge rate is extremely slow relative to withdrawal, hydrogeologists including those cited in Sandra Postel's Pillar of Sand (1999) have long warned that portions of it face effective long-term exhaustion under current pumping regimes.