With California already suffering through a devastating drought, another water catastrophe has emerged: The state is quickly depleting its groundwater reserves.
Reservoirs, creeks, and rivers usually supply a large portion of California’s water for drinking and irrigation. With that water in short supply, farmers pump groundwater by drilling wells. Because of the drought, groundwater is now furnishing close to 70 percent of the state’s water, up from 40 percent in a typical year, according to Jay Famiglietti, a hydrologist at the University of California, Irvine.
“We’re poised for a major run on groundwater,” he said, noting that water restrictions have sparked a well-drilling frenzy in some regions, leading people to drain groundwater faster than it can be replaced. A state report released in May shows that groundwater levels have hit record lows since 2008.
Worse, California lacks a statewide system to regulate groundwater pumping. But that could soon change. State lawmakers have approved a bill requiring local agencies to develop groundwater-management plans, and the state will release a draft blueprint later this year—which could lead to the monitoring and reporting of groundwater withdrawals, restrictions on how much farmers can pump, and fines for pumping too much.
The key to enforcing the law: satellites. They’re already giving scientists a bird’s-eye view of underground water resources—and could be central to providing the state with detailed information about how much groundwater remains and how much water farms consume.
“We need more detailed information to actively manage the water basins,” said Lester Snow, executive director of the California Water Foundation in Sacramento and a former director of the California Department of Water Resources.
Since 2003, Famiglietti has been using data from GRACE, a joint U.S.-German satellite mission, to monitor groundwater depletion from space. The data show that water levels in the San Joaquin and Sacramento river basins were at their lowest levels in a decade by December 2013.
The Central Valley’s reserves are shrinking by 800 billion gallons a year. Famiglietti also sees close correlations between surface water allocations and groundwater reserves. When allocations are high, groundwater levels recover, but when they’re restricted—as they are now—“groundwater is hit very hard,” he said.
GRACE can give California an overview of its groundwater resources, but it can’t tell officials how much groundwater each farm uses.
Groundwater used for irrigation ends up in one of three places: It evaporates from the ground, is soaked up by growing plants, or trickles into the soil to recharge the groundwater. Plants also release some of the water as vapor (called transpiration) during photosynthesis.
Although a water meter attached to a groundwater pump can track how much water a farmer withdraws from the ground, it doesn’t show how much is returned to the aquifer or lost to the air by evaporation or transpiration.
Satellites can also provide detailed information about this water loss—how much water agricultural producers withdraw permanently from the system. Richard Allen, a water resources engineer at the University of Idaho, uses images of vegetation and temperature from a Landsat satellite to calculate rates of evapotranspiration and estimate water use. He feeds the information into a computer model called METRIC (Mapping Evapotranspiration at High Resolution With Internalized Calibration), which allows him to see how much water is being consumed from one field to the next.
METRIC has been used in Idaho to quantify groundwater consumption from the Snake River Plain aquifer, which supports two million acres of irrigated land. Allen said METRIC helps monitor and manage water rights, identify illegal pumping, and provide better information about consumption.
“If farmers were asked to pay for groundwater, METRIC could give an accurate assessment of pumping over the course of a growing season,” said Allen. “We could send you an image that shows you how much water you used.”
Although there’s interest in California to include satellite-based measurements of groundwater and its consumption, bridging the gap between research and statewide operation takes time. But Famiglietti remains optimistic. “The results we have been getting are good, and they’re only going to get better,” he said.