The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [54]
We are now coming to appreciate just how widespread this problem is globally, by measuring small variations in the Earth’s gravity field precisely from space. In 2009 researchers using the NASA Gravity Recovery and Climate Experiment (GRACE) satellites discovered that despite natural recharge, groundwater tables in heavily irrigated parts of the Indian subcontinent are falling between four and ten centimeters per year, an unsustainable decline in an area supporting some six hundred million people.232
Most irreversible is groundwater overdrafting in our driest places. Not only do these aquifers have very low rates of rainfall recharge—and thus faster overdraft—but they are very often the main or only water source upon which people depend. Once gone, they take thousands of years to refill, or may never refill at all because they are relicts left over from the end of the last ice age. For all intents and purposes fossil groundwater, like oil, is a finite, nonrenewable resource. Eventually, the wells must run dry.
Death of a Giant
The Ogallala is a monster aquifer underlying no fewer than eight states across the western United States.233 Its existence had been known to High Plains ranchers and dryland farmers since the 1800s, but it wasn’t until the 1940s—with the arrival of modern pumps powered by electricity or natural gas—that the spigot could be opened wide. Since then, we have been pumping seven trillion gallons of cold, clear water out of the Ogallala Aquifer to irrigate circular center-pivot fields of wheat, cotton, corn, and sorghum across the Great Plains. This soon transformed over one hundred million acres of highly marginal land—much of it abandoned after the 1937 Dust Bowl—into one of the world’s most productive agricultural regions. From your airplane window or a Web-browser view from Google Earth, you can see for yourself the green circles stamped out across the Texas and Oklahoma panhandles through eastern Colorado, New Mexico, and Wyoming; and running north through Kansas and Nebraska all the way to southern South Dakota. Those verdant, neatly aligned disks are the telltale fingerprints of the Ogallala Aquifer.
Zoom in with your Web browser and you’ll see many of the disks are brown. By 1980 it was common knowledge that wells were falling fast in the Ogallala’s southern half. By 2005 large portions had fallen by 50 feet, 100 feet, even 150 feet, in southwestern Kansas, Oklahoma, and Texas. Wells in the wetter northern half were holding up fine thanks to much higher natural recharge rates, but the dry southern states, where the Ogallala water is mostly of Pleistocene age,234 was in serious overdraft. Wells began sputtering. Texas farmers, accustomed to feeding one or more center-pivot fields from a single well, began drilling several wells to support a single field.
In 2009 a team led by Kevin Mulligan, a professor of economics and geography at Texas Tech, completed a detailed study of just how fast Texas farmers are emptying out the southern Ogallala. Using a Geographic Information System (GIS), his team mapped thousands of wells throughout a forty-two-county area of northern Texas. They used the wells’ water-level and flow-rate data to calculate the remaining saturated thickness of the Ogallala, and how fast the water table is falling. From these data they constructed a series of maps projecting the remaining useful life expectancy of the aquifer, for ten, fifteen, and twenty-five years into the future.
The results were shocking. Texas’ Ogallala Aquifer is dropping an average of one foot per year and in some places as much as three feet per year. Many areas are careening toward a saturated thickness of just thirty feet, at which point the last wells will begin to suck air.235 These maps are incredibly precise—all of the thousands of individual wells and the green crop circles they support