Study predicts more extreme storms for California in the future

BOSTON, Jan. 3 (UPI) -- Scientists believe a warmer climate will deliver more extreme storms to California, like the one that dropped three inches of rain on San Francisco in just an hour in 2014, triggering flooding and mudslides.

According to new models developed by scientists at MIT, a rise in global temperature of 4 degrees Celsius will yield an extra three extreme precipitation events per year in California by the end of the century.

"One of the struggles is, coarse climate models produce a wide range of outcomes. [Rainfall] can increase or decrease," Adam Schlosser, senior research scientist in MIT's Joint Program on the Science and Policy of Global Change, said in a news release. "What our method tells you is, for California, we're very confident that [heavy precipitation] will increase by the end of the century."

Most models predict future precipitation by analyzing large scale climate trends. These models have trouble integrating local factors like moisture convection and topography. As part of their prediction efforts, scientists decided to forgo local precipitation forecasting in favor or large-scale atmospheric patterns.

"We've actually found there's a connection between what climate models do really well, which is to simulate large-scale motions of the atmosphere, and local, heavy precipitation events," Schlosser said. "We can use this association to tell how frequently these events are occurring now, and how they will change locally, like in New England, or the West Coast."

Scientists looked extreme precipitation events in California and the Midwest between 1979 to 2005, paying special attention to the two most influential factors, wind currents and moisture content.

"We essentially take snapshots of all the relevant weather information, and we find a common picture, which is used as our red flag," Schlosser explained. "When we examine historical simulations from a suite of state-of-the-art climate models, we peg every time we see that pattern."

Researchers then looked at how larger climate trends, like global warming, will influence these two factors through 2100. The new models -- reflecting a warming climate -- revealed a higher frequency of red flags, the patterns associated with heavy storms.

Schlosser and his colleagues detailed their process in the Journal of Climate. The same team of scientists is now working on building a similar model to predict the prevalence of heat waves.