Global Warming Upped Heat Driving California’s Drought


A view from Monument Peak Ridge in the Trinity Alps taken in May, 2014.Trinity Lake, one of California’s largest reservoirs, is in the distance with a noticeable bathtub ring. Credit: Gary Robertson/Flickr

Global Warming Upped Heat Driving California’s Drought

Brian Kahn March 2nd, 2015

Despite a recent influx of snow and rain this past weekend, extremely low snowpack in the Sierra Nevada has conspired with warm temperatures to keep the state in the grips of one its worst droughts on record for at least another year. The precipitation has been the key ingredient to start the drought, but heat has played an important role in maintaining and intensifying it. A new paper published Monday in the Proceedings of the National Academy of Science shows that human greenhouse gas emissions have helped increase the odds in favor of warm, dry conditions for the Golden State. More ominously, the results suggest that by 2030, the warm weather driving the current drought could become a yearly occurrence. The current California drought began at the end of 2011, when a failed rainy season sparked moderate drought conditions around the state. Since then, it has expanded and strengthened, with nearly 40 percent of the state in the most severe type of drought listed by the U.S. Drought Monitor as of last week. Record warmth has helped keep those drought conditions locked in place.

The hot, dry weather has had huge impacts from exacting at least $2.2 billion in agricultural losses to literally moving mountains as farmers have drawn down historic amounts of groundwater to supplement meager rainfall. Urban areas have implemented water rationing programs and some ski areas have been forced to stop their lifts as snow has all but disappeared in the Sierra Nevada this year. Much has been made of the ridiculously resilient ridge, a block of high pressure that’s deflected storms to the north of the state. There have been hints of climate change in the ridge’s persistence but nothing conclusive about the drought. The new research published in the Proceedings of the National Academy Science turns its eye on temperature as a confounding variable and finds climate change is much more definitively connected. “There’s no question that low precipitation is a prerequisite for severe drought in California but it’s not sufficient,” Noah Diffenbaugh, a senior fellow at the Woods Institute for the Environment at Stanford University, said. “The efficiency of low precipitation turning into severe drought is much higher if there are warm conditions.”

Diffenbaugh led the new research, which analyzed 20 moderate to severe droughts that are on record for California going back to 1896. Those droughts have occurred twice as often since 1995. Wet season precipitation hasn’t changed noticeably over that time period. The big shift has been temperature….

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