While the scientific jury is still out as to whether or not human-caused climate change is the source of extreme storms and other natural disasters, scientists say climate change has increased global warming, which in turn increases California’s risk for drought, according to a September 2014 report examining recent extreme weather events.
“Human-caused climate change has increased the likelihood of extremely high atmospheric pressure over the North Pacific Ocean, which suggests an increased risk of atmospheric patterns conducive to drought in California,” summarized Daniel Swain, a PhD candidate in environmental earth system science at Stanford University, on Weather West, his blog on California weather. Swain is a co-author of The Extraordinary California Drought of 2013/2014: Character, Context, and the Role of Climate Change, a paper included in a special bulletin of the American Meteorological Society report “Explaining Extreme Events of 2013 from a Climate Perspective.” Twenty different research groups from around the world explored 16 various 2013 weather events, including California’s drought, and tried to determine which, if any, were caused or affected by human-generated climate change. In short, they concluded that the scientific tools and the historical data available today make it unclear if some events are the sole result of human-caused climate change or just natural variations. One exception was global warming and heat waves, “The findings indicate that human-caused climate change greatly increased the risk for the extreme heat waves assessed in this report.”
What Caused California’s Drought?
California’s drought of 2013-2014 was the most severe in its history and has been deemed an “extreme event” by climate scientists. The state declared a “drought emergency,” and all 58 counties have been declared federal disaster areas. A combination of record high sea surface temperatures, other conditions, and a shifted jet stream changed seasonal patterns that historically bring a series of wet storms to California from late October to May. Drought occurs when these storms fail to reach the state and replenish its water “bank,” most of which is held in the form of snow in the Sierra Nevada mountains that later melts and fills reservoirs.
In looking at climate models, Swain and his co-authors found that conditions that block California’s “normal” winter storm pattern “occur much more frequently in the present climate than in the absence of human emissions.”
Regardless of the cause, California could be in for continued dry conditions and water hardship following three winters of record low precipitation. The report was inconclusive as to if weather conditions that extend the current drought will persist through this winter.
Already, the state has curtailed water deliveries to farms in the central valley, the nation’s premier growing area, instituted mandatory water conservation, and passed historic legislation to limit groundwater pumping. Rural towns are beginning to run out of water. The drought has caused millions of dollars in farming losses, and increased prices for produce and beef as fields go dry, and water-intensive crops are reduced. (Read “California’s Bitter Drought”) Tensions have also risen between environmentalists and central valley farmers who see each other as competitors for dwindling water supply.
So much water has is being pumped from the aquifers beneath the central valley that the ground settlement can be measured by satellite. And the Sierra Nevada mountain range is rising as the earth’s crust uplifts from the loss of so much water.
While scientists are still studying how global warming and the melting of the northern sea ice is affecting the atmosphere and weather patterns, there is no doubt that California was experiencing its warmest year on record in 2014 and increased land temperatures amplify drought conditions by further drying out the soil.
Understanding the link between climate change and California droughts will be vital to assessing the state’s future risk of severe droughts and how to best prepare for it.