http://news.nationalgeographic.com/2016/12/groundwater-depletion-global-food-supply/
Rising temperatures and growing demands for thirsty grains like rice and wheat could drain much of the world’s groundwater in the next few decades, new research warns.
Nearly half of our food comes from the warm, dry parts of the planet, where excessive groundwater pumping to irrigate crops is rapidly shrinking the porous underground reservoirs called aquifers. Vast swaths of India, Pakistan, southern Europe, and the western United States could face depleted aquifers by mid-century, a recent study finds—taking a bite out of the food supply and leaving as many as 1.8 billion people without access to this crucial source of fresh water.
To forecast when and where specific aquifers around the globe might be drained to the point that they’re unusable, Inge de Graaf, a hydrologist at the Colorado School of Mines in Golden, Colorado, developed a new model simulating regional groundwater dynamics and withdrawals from 1960 to 2100. She found that California’s agricultural powerhouses—the Central Valley, Tulare Basin, and southern San Joaquin Valley, which produce a plentiful portion of the nation’s food—could run out of accessible groundwater as early as the 2030s. India’s Upper Ganges Basin and southern Spain and Italy could be used up between 2040 and 2060. And the southern part of the Ogallala aquifer under Kansas, Oklahoma, Texas, and New Mexico could be depleted between 2050 and 2070.
A 2015 study based on satellite observations showed that most of the world’s largest aquifers—21 out of 37—are being drained faster than they can refill. “A number of studies point to the overuse of groundwater and the tremendous risk that our water and food security are under,” says water scientist Jay Famiglietti of the NASA Jet Propulsion Laboratory, who led the satellite study. “The problem is, we don’t know how much groundwater is left.”
De Graaf’s study begins to address that problem for regional aquifers. In normal conditions, those layers of sand or porous rock are recharged by water from rain, snow, or streams seeping down through the ground. But recharge can’t keep up with today’s furious pace of pumping, especially in areas that receive little precipitation.
