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California droughts caused mainly by changes in wind, not moisture

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California droughts caused mainly by changes in wind, not moisture

Posted: 05 Jul 2016 07:26 AM PDT

Droughts in California are mainly controlled by wind, not by the amount of evaporated moisture in the air, new research has found. The research increases the understanding of how the water cycle is related to extreme events and could eventually help in predicting droughts and floods. … “Ocean evaporation has little direct influence on California precipitation because of its relatively weak variability,” Wei said.
Instead, the researchers found that disturbances in atmospheric circulation, the large-scale movement of air, have the most effect on drought because they can affect factors that will cause it to rain more or less.

….Most of California has been in a severe drought since 2011, although a strong El Niño in the winter of 2015 helped diminish the drought. The current drought is caused by a high-pressure system that disturbs the atmospheric circulation. The development of the high-pressure system is related to a sea surface temperature pattern in the Pacific Ocean, according to research cited by the study.

Although this is a very rare event, the probability of this kind of high-pressure system is likely increasing with global warming,” the authors said. Yang said that the research could aid in the prediction of droughts and floods by improving scientific understanding of the intricate factors that influence rainfall the most. “The topic is extremely timely as current and future climate change would mean more changes in extreme events such as droughts and floods,” Yang said. “Understanding this asymmetric contribution of ocean evaporation to drought and flooding in California will ultimately help us make better predictions.”

Jiangfeng Wei, Qinjian Jin, Zong-Liang Yang, Paul A. Dirmeyer. Role of ocean evaporation in California droughts and floods. Geophysical Research Letters, 2016; DOI: 10.1002/2016GL069386


This is California as viewed from the International Space Station.

Credit: NASA, Stuart Rankin

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