California's drought was spawned by natural weather variations that have bedeviled the West throughout recorded history.
But a new study released Thursday says human-caused global warming is worsening the natural phenomenon. The study by Columbia University's Earth Institute isn't the first to say warming has played a key role in fueling California's dry conditions, but it is the first to measure its impact, predicting that it increased the problem by as much as 25 percent.
Weather patterns that push away the rain-carrying moisture in the atmosphere are normal for the state. But warming adds to the resulting dryness and heat. Some of the moisture stored in plants and the soil evaporates into the drier atmosphere.
"A lot of people think that the amount of rain that falls out the sky is the only thing that matters," said Park Williams, a bio-climatologist at Columbia University's Lamont-Doherty Earth Observatory who was the study's lead author. "But warming changes the baseline amount of water that's available to us because it sends water back into the sky."
Lightning strikes on parched earth are igniting wildfires all over the state. There are so many blazes that firefighters from across the world are rushing to help put them out.
In the Central Valley, the land is so dry that farmers are drilling deep into the soil to extract groundwater to irrigate crops. The drilling and pumping draws down aquifers that serve as a sort of liquid bank the state relies on when drought strikes and rivers and reservoirs aren't replenished by rain and snow.
The current drought is the most severe on record, state officials say, and 2014 was the hottest year in state history. Snowpack in the Sierra Nevada that recharges aquifers across the state was near zero, and there has been little rainfall. Californians are hoping that a giant El Niño weather pattern forming in the Pacific Ocean will deluge the state with rain next winter.
Even a large seasonal gusher would only delay the inevitable — a future of longer and more frequent drought in California, numerous researchers have said.
In February, researchers at NASA, Cornell and Columbia universities predicted that California and the southwest will slip into a 30-year megadrought by 2050 if greenhouse gas emissions are not curtailed.
A month later, researchers at Stanford University predicted increases in average temperatures will continue, leading to quick evaporation of rainfall and increasing the likelihood of prolonged dryness.