WATER SECURITYHow California’s Farmers Can Recharge the Aquifers They’ve Drained
Agriculture requires a lot of water. In the drought-stricken Central Valley, researchers have found a win-win for growers.
In parts of California’s Central Valley, so much groundwater has been pumped out of the ground to deal with the region’s persistent drought that the land is starting to sink in. Underground aquifers — layers of sand, gravel, clay, and water — are vital resources that communities can turn to when surface water is scarce. But when more water is pumped out of aquifers than is put back in — as is happening in the southern part of the valley — it can cause the ground to slowly contract, like a drying sponge.
After studying this phenomenon, Rosemary Knight, a professor of geophysics at the Stanford Doerr School of Sustainability, became interested in identifying the fastest ways to replenish California’s groundwater using managed aquifer recharge. This technique involves flooding a piece of land with excess surface water and allowing that water to seep through the ground and into aquifers, where it can be stored for later use. Armed with a massive electromagnetic dataset, Knight and a team of researchers set out to analyze sediment types below the surface in the California Central Valley and map out the quickest routes to refilling aquifers.
Their research, published last month in the journal Earth and Space Science, found that between 2 million and 7 million acres of land in the Central Valley are suitable for recharge — or between 19 and 56 percent of the valley’s total area. Most of the rechargeable land is currently used to grow crops. Many farmers are enthused about the data, according to Knight — and keen to implement it. As climate change continues to exacerbate water challenges in California, her team’s research points to how agricultural producers can help to ensure sustainable water access for all. “They want to be part of the solution,” said Knight.
Since 2000, the U.S. Southwest has been in the driest 25-year period the region has seen in over a millennium, according to researchers at the University of California, Los Angeles, who found that climate change has supercharged these dry conditions.
