Global warming has worsened California's drought

Doyle Rice | USA TODAY

Man-made global warming has made California's historic drought 15% to 20% worse than it would have been and will likely make future droughts even worse, a study published by the American Geophysical Union said Thursday.

California could also face nearly permanent drought conditions by the second half of this century, the study said.

The warming temperatures are making the drought worse because the extra heat draws moisture out of plants and soil, exacerbating the dryness, according to the study.

“A lot of people think that the amount of rain that falls out the sky is the only thing that matters” in a drought, said lead author A. Park Williams, a bioclimatologist at Columbia University. “But (global) warming changes the baseline amount of water that’s available to us, because it sends water back into the sky” through evaporation.

The study said statewide average temperatures have been creeping higher — about 2.5 degrees over the 114 years the scientists studied, which is in step with rising man-made emissions from fossil fuels.

The study appeared in the peer-reviewed journal Geophysical Research Letters, a publication of the American Geophysical Union.

The drought has also contributed to wildfires that have charred more than 100,000 acres across California, more than twice the average, according to CalFire, the state firefighting agency. It's also drying up wells and affecting the state's agricultural economy.

Martin Hoerling, a research scientist with the National Oceanic and Atmospheric Administration who was not involved in the study, noted that many scientists say warming temperatures are making droughts more severe, but "there is less agreement on how large that effect is."

"In California, adaptation to a dry climate has been happening for over a century and will continue to occur," said Hoerling, who authored a report last year on the topic. "Climate change is only one of many pressing demands on water, and all are part of a complicated and interwoven policy and social context through which the state;s water supply is distributed."

A separate drought-related study from NASA out Wednesday found that land in California's fertile San Joaquin Valley is sinking faster than ever before, nearly 2 inches per month in some locations. It's happening because huge amounts of groundwater are being pumped out for irrigation, as surface water supplies in reservoirs running low.

The sinking land has the potential to damage local, state and federal infrastructure, including aqueducts, bridges, roads and flood control structures, the study said.

“Groundwater acts as a savings account to provide supplies during drought, but the NASA report shows the consequences of excessive withdrawals as we head into the fifth year of historic drought,” California Department of Water Resources Director Mark Cowin said.