Heavy Groundwater Use Causes Record Land Subsidence
NASA and the California Department of Water Resources (DWR) on Wednesday released a new report documenting severe land subsidence in the state’s heavily agricultural Central Valley. Most of the damage is concentrated in the San Joaquin Valley, which is sinking faster than ever before because of massive groundwater pumping triggered by the ongoing drought.
In some cases, the land surface is dropping by as much as 2 inches per month.
Land near Corcoran in the Tulare Basin sank 13 inches in just eight months – about 1.6 inches per month. One area in the Sacramento Valley was sinking by approximately half an inch per month, faster than previous measurements.
NASA also found that areas near the California Aqueduct sank by up to 12.5 inches, with eight inches of that occurring in just four months of 2014. This subsidence is damaging the aqueduct itself, which, ironically, was originally built to prevent further subsidence. The sinking land is causing the 444-mile concrete aqueduct to slump and crack, reducing its capacity to move water and creating leaks.
By delivering water imported from rivers hundreds of miles north, it was thought that reliance on groundwater in the San Joaquin Valley could be reduced, thereby preventing further subsidence. But as agriculture has grown and imported water supplies diminished, groundwater pumping has again become extreme.
NASA obtained the subsidence data by comparing satellite images of the Earth’s surface over time. Click here for the full report in pdf form.
“Groundwater levels are reaching record lows – up to 100 feet lower than previous records,” said DWR director Mark Cowin. “As extensive groundwater pumping continues, the land is sinking more rapidly and this puts nearby infrastructure at greater risk of costly damage.
“Groundwater acts as a savings account to provide supplies during drought,” Cowin said in a statement, “but the NASA report shows the consequences of excessive withdrawals as we head into the fifth year of historic drought.”
On Wednesday, DWR also released a draft list and maps describing “critically overdrafted” groundwater basins throughout the state. Most of these are in the San Joaquin Valley.
California passed sweeping new groundwater laws in 2014 – a first for the state. But the regulations don’t take full effect for two decades, meaning groundwater overdraft is likely to remain common practice for some time.
If the Drought Continues for Three More Years…
The Public Policy Institute of California (PPIC) examines this hypothesis in a new report out today. It states that while the state was “unprepared” for a drought of this magnitude, urban areas have managed well and would likely continue to do so if the crisis continues.
“Californians have worked hard to limit its impacts,” Ellen Hanak, director of the PPIC Water Policy Center, told the Los Angeles Times, “but the experience has also revealed major gaps in our readiness to cope with the droughts we expect in the future.”
Among the gaps are rural areas and natural habitat. Many small communities are struggling now, and that pain will spread if the drought continues. In addition, an extended drought, according to the study, would threaten extinction for 18 native species of fish and higher rates of mortality among migratory waterfowl.
“If the drought continues, emergency programs will need to be significantly expanded to get drinking water to rural residents and prevent major losses of waterbirds and extinctions of native fish species,” said Jeffrey Mount, PPIC senior fellow. “California needs a longer-term effort to build drought resilience in the most vulnerable areas.”
Study: Climate Change Has Significant Role in California Drought
A new studypublished by the journal Geophysical Research Letters finds that climate change has worsened the California drought by as much as 27 percent.
Experts have been probing the link between climate change and drought in California for several years, with conflicting results. But scientists not involved in the latest study described it as more thorough than any previous effort, because it analyzed nearly every possible combination of data on temperature, rainfall, wind speed and other factors that could be influencing the severity of the drought.
The group, led by Dr. A. Park Williams, a climate scientist at Columbia University, concluded that human-caused climate change was responsible for between 8 percent and 27 percent of the deficit in soil moisture that California experienced from 2012 to 2014.
Since 1895, California has warmed by a little more than 2 degrees Fahrenheit. That increase sounds small, but as an average over an entire state in all seasons, scientists say, it is a large number. The warmer air can hold more water vapor, and the result is that however much rain or snow falls in a given year, the atmosphere will draw it out of the soil more aggressively.
“It would be a fairly bad drought no matter what,” Williams told the New York Times. “But it’s definitely made worse by global warming.”
Headline image: This map, released Wednesday by the state, shows groundwater basins identified in a state of “critical overdraft,” meaning they are being pumped out much faster than they are being replenished by nature. Most are in the San Joaquin Valley, a farming region heavily dependent on groundwater and surface water imported from rivers to the north. Images courtesy California Department of Water Resources