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Study Finds California Drought and Eastern Storms Linked

Thursday, Feb. 19, 2015

USU faculty member and researcher Simon Want

Simon (Shih-Yu) Wang, assistant professor in the USU Department of Plants, Soils and Climate and lead author of the new study, and his colleagues, find that human activity is driving weather events to greater extremes.

Despite heavy but spotty rainfall in recent months, the drought in California and other parts of the West is expected to continue and intensify, and the atmospheric anomaly behind the drought is also pushing record snowfall and cold temperatures in the Eastern United States, again.

A study of the causes of the recent California drought found a strong and persistent high pressure ridge over the West Coast developed at the same time as a low pressure trough developed in the East, both related to changes in ocean temperatures. The results of an examination of 17 climate models — aimed at understanding and predicting these climate events — by scientists at Utah State University, Taiwan Normal University and the Pacific Northwest National Laboratory was released this week [Feb. 16] in Atmospheric Science Letters, published by the Royal Meteorological Society.

Though a report issued in November by the National Oceanic and Atmospheric Administration (NOAA) questioned a link between human-caused climate change and these exceptional weather events, Simon (Shih-Yu) Wang, assistant professor in the USU Department of Plants, Soils and Climate and lead author of the new study, and his colleagues find that human activity is driving weather events to greater extremes. The NOAA report also emphasized changes in average or mean precipitation over the coming decades, but this new study says it is the year-to-year variation that is increasing and of concern.

“Our new study focuses on the pathway in which warming in the western Pacific Ocean influences a very persistent weather pattern that is reducing rainfall in California,” Wang said. “We also differentiate between mean amounts of precipitation and what we expect will be wide variations in precipitation. Most climate models project that in the next few decades winter rainfall in California will gradually increase with a warmer climate. But we find that it will also be punctuated with years of extreme drought and years of extreme precipitation.”

Jin-Ho Yoon of the Pacific Northwest National Laboratory and a co-author of the newly published study, points out that only looking at predictions of long-term mean rainfall and temperature doesn’t tell the whole story.

“Precipitation variation is amplified by greenhouse gases in the atmosphere,” Yoon said. “It means very wet winters could follow a period of prolonged or intense drought. So only looking at long-term mean rainfall doesn’t tell much of future climate extremes.”

“People must live with the extremes,” Wang said. “If you have an almond orchard or grow crops, it doesn’t help when all the rain you expected for several months falls in one or two days, and you can’t capture or manage it, and then you get no precipitation for months afterward. People don’t live in the mean climate. Our studies of climate models and understanding how climate works can help governments and citizens prepare for future similar events. Understanding the ‘pathway’ illustrated in our analyses can help forecast future drought.”

The paper, The North American Winter ‘Dipole’ and Extremes Activity: a CMIP5 Assessment, published in Atmospheric Science Letters, is available online.

Related links:

USU Department of Plants, Soils and Climate

USU College of Agriculture and Applied Science

Contact: Simon Wang, 435-797-3121,

Writer: Lynnette Harris, 435-797-2189 (office), 435-764-6936 (cell),

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