The report from UC Irvine’s Center for Hydrologic Modeling is an update to a 2011 study which showed the basins lost nearly as much water as the volume of Lake Mead over a seven year period.
The new report finds water storage in the last two years continues to plummet, and the study doesn’t even include the most recent dry winter.
Report author Jay Famiglietti says the amount of water lost is equal to the water used by all of California’s urban areas each year. Most of the loss is due to groundwater withdrawals.
Famiglietti says groundwater levels drop faster during drought than they can be replenished during wet periods.
“This is a worse than ever situation," says Famiglietti. "So we really have to watch what’s going to happen with the groundwater. It’s been bad in the past during drought periods and now with a zero surface water allocation I’m quite concerned that it will be terrible in the future.”
January brought above-average rainfall and snow to much of California, partly due to El Niño. But forecasters say the ocean warming condition is "taking a break" for the next week or longer.
The U.S. Drought Monitor says, other than a slight reduction in exceptional drought in the northern Sierra, it needs more time to assess impacts of the recent moisture on California's long-term drought.
California regulators have made modest adjustments to water conservation requirements for cities.
The second measurement this winter of snowpack in the Sierra Nevada was 130 percent of average. State water officials say the snowpack will help reservoir recovery.
California's water conservation rate dropped to 18 percent in December. But water regulators say the state continues to meet its long term goals.