Scientists find evidence showing hazardous weather to increase in U.S. California

LOS ANGELES, Aug. 12 (Xinhua) -- A group of scientists from the U.S. states of California, Nevada and Colorado have found evidence that the risk of hazardous weather is increasing in the Golden State, a report of the University of California (UC) said Thursday.

This research, investigating the daily relationships among four major modes of weather affecting California, was led by Kristen Guirguis, a climate researcher at Scripps Institution of Oceanography at UC San Diego.

The four dominant atmospheric circulation patterns over the North Pacific Ocean were known as Baja-Pacific, Alaskan-Pacific, Canadian-Pacific, and Offshore-California modes.

They interact with each other daily and create 16 recurring weather patterns which form extreme weather events such as atmospheric rivers capable of bringing torrential rains and Santa Ana winds that can spread devastating wildfires.

One product of the work was a summary of California weather patterns from 1949 to 2017, which proved that the patterns associated with the formation of dry gusty Santa Ana winds that often stoke Southern California fires are becoming more frequent.

Meanwhile, patterns associated with what might be considered "normal" rainfall are decreasing in the Southwest thus promoting drought, but patterns associated with extreme precipitation and strong atmospheric river episodes have remained steady over the study period.

The researchers noted that while the patterns associated with heavy precipitation and strong atmospheric rivers have not changed in frequency, a warmer atmosphere is capable of holding more water so these storms are becoming more damaging, especially in winter.

"Though winter atmospheric rivers are the antithesis of hot, dry Santa Ana wind conditions, sequences of wildfires followed by strong atmospheric rivers often compound the damage from fires when they trigger flash floods and destructive debris flows from burn scars," the report explained.

Guirguis was also quoted a saying that this study suggested that weather patterns were changing in a way that enhances hot, dry Santa Ana winds, while reducing precipitation frequency in the Southwest and these changes would rise the risk of wildfires during California winters.

The study, "Winter wet-dry weather patterns driving atmospheric rivers and Santa Ana winds provide evidence for increasing wildfire hazard in California," has been published in the journal Climate Dynamics.

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