Californians Should Gear Up For More Extreme Weather

The atmospheric patterns related to droughts in California have happened frequently in recent times. The state has moved towards extreme weather, according to a study by Stanford University scientists. They analyzed large-scale circulation patterns that took place during California's extreme historical precipitation and temperature changes over the years.

"The current record-breaking drought in California has arisen from both extremely low precipitation and extremely warm temperature," said Noah Diffenbaugh, senior author of the study. "In this new study, we find clear evidence that atmospheric patterns that look like what we've seen during this extreme drought have in fact become more common in recent decades."

Diffenbaugh and his team studied atmospheric pressure patterns like those that took place during California's historical weather events. They tried to find out if they recently occurred with a different frequency.

By using historical climate data from United States government archives, the team could reveal changes during its "rainy season" from October to May. The team focused on identifying the specific North Pacific atmospheric patterns linked with the extreme temperature and precipitation seasons happening between 1949 and 2015.

There seemed to be a significant increase in atmospheric patterns related to extreme temperature and precipitation seasons over the 67 years they studied. There seemed to be a steady increase in patterns that were closely linked to those observed in the latter half of its ongoing drought.

"California's driest and warmest years are almost always associated with some sort of persistent high-pressure region, which can deflect the Pacific storm track away from California," said Daniel Swain, first author of the study. "Since California depends on a relatively small number of heavy precipitation events to make up the bulk of its annual total, missing out on even one or two of these can have significant implications for water availability."

Due to this "high" pushing winter storms away from California, there is a crucial lack of water supply  with about 75 percent of the state's precipitation in the coldest months. Moreover, the blocking pushes temperatures higher on land and in coastal oceans.

Still, California has not undergone a decline in wet atmospheric patterns.

"We're seeing an increase in certain atmospheric patterns that have historically resulted in extremely dry conditions, and yet that's apparently not occurring at the expense of patterns that have historically been associated with extremely wet patterns," Swain said. "We're not necessarily shifting toward perpetually lower precipitation conditions in California - even though the risk of drought is increasing."

Hence, extreme weather conditions in California are showing an increase. Residents should gear up for "more warm and dry periods, punctuated by wet conditions."

The findings were published  in the April 1, 2016, issue of Science Advances.