From The Scripps Institution of Oceanography At The University of California-San Diego : “More Evidence that California Weather Is Trending Toward Extremes”

From The Scripps Institution of Oceanography


The University of California-San Diego

Robert Monroe

Chaparral Fire in 2021.Photo credit: JeffHall / Cal Fire.

A team led by Kristen Guirguis, a climate researcher at Scripps Institution of Oceanography at UC San Diego, found evidence that the risk of hazardous weather is increasing in the Southwest.

The researchers investigated the daily relationships among four major modes of weather affecting California. How they interact governs the formation of weather events such as atmospheric rivers capable of bringing torrential rains and Santa Ana winds that can spread devastating wildfires.

“This study suggests that weather patterns are changing in a way that enhances hot, dry Santa Ana winds, while reducing precipitation frequency in the Southwest,” said Guirguis. “These changes in atmospheric circulation are raising the risk of wildfires during California winters.”

The study was published in the journal Climate Dynamics [below] July 17, 2022.

The basis of the research was an examination of the dominant atmospheric circulation patterns over the North Pacific Ocean, known as Baja-Pacific, Alaskan-Pacific, Canadian-Pacific, and Offshore-California modes. What distinguishes them from each other are the relative positions of ridges and troughs in the atmosphere.

Dillard Road is flooded near the Hwy 99 off ramp, located south of Elk Grove, California. Photo credit: Florence Low / California Department of Water Resources.

The research team identified 16 recurring weather patterns that are created daily as these modes interact with each other. One product of the work was a summary of California weather patterns from 1949 to 2017. The patterns associated with the formation of dry gusty Santa Ana winds that often stoke Southern California fires are becoming more frequent. 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 [Earth’s Future (below)] is capable of holding more water so these storms are becoming more damaging.

The results suggest an increasing probability of compounding environmental hazards during California winters, said the research team. 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.

Photo of the Thomas Fire taken from a Santa Barbara beach. Photo credit: Carsten Schertzer / iStock.

“This spells challenges for wildfire and water resource management and provides observational support to our previous results [ScientificReports (below)] projecting that California will increasingly have to depend on potentially hazardous atmospheric rivers and floodwater for water resource generation in a warming climate,” said study co-author Alexander Gershunov, a Scripps Oceanography climate scientist.

Study authors say this work is helping to inform an experimental subseasonal-to-seasonal (S2S) forecast product being developed at Scripps Oceanography’s Center for Western Weather and Water Extremes (CW3E) that predicts extreme weather in California including atmospheric river landfalls, Santa Ana winds, drought, and heat waves.

The U.S. Department of the Interior via the Bureau of Reclamation and the Southwest Climate Adaptation Science Center, the California Department of Water Resources, and the Regional Integrated Sciences and Assessments (RISA) California—Nevada Climate Applications Program and the International Research Applications Program of the National Oceanic and Atmospheric Administration funded the study. Additional funding was provided by the University of California Office of the President MRPI grant.

High water levels on the Tuolumne River close River Road in the city of Modesto, California, part of Stanislaus County. Photo credit: Dale Kolke / California Department of Water Resources.

Study co-authors include Benjamin Hatchett of the Desert Research Institute in Nevada; Tamara Shulgina, Michael DeFlorio, Rosana Aguilera, achel Clemesha, Tom Corringham, Luca Delle Monache, and Marty Ralph of CW3E at Scripps Oceanography; Aneesh Subramanian and David Reynolds of the University of Colorado Boulder; Janin Guzman-Morales of the University of California Santa Barbara; and Alex Tardy and Ivory Small of the National Weather Service.

Science papers:
Climate Dynamics
Earth’s Future

See the full article here .


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A department of The University of California-San Diego, The Scripps Institution of Oceanography is one of the oldest, largest, and most important centers for ocean, earth and atmospheric science research, education, and public service in the world.

Research at Scripps encompasses physical, chemical, biological, geological, and geophysical studies of the oceans, Earth, and planets. Scripps undergraduate and graduate programs provide transformative educational and research opportunities in ocean, earth, and atmospheric sciences, as well as degrees in climate science and policy and marine biodiversity and conservation.

The University of California-San Diego is a public research university located in the La Jolla area of San Diego, California, in the United States. The university occupies 2,141 acres (866 ha) near the coast of the Pacific Ocean with the main campus resting on approximately 1,152 acres (466 ha). Established in 1960 near the pre-existing Scripps Institution of Oceanography, The University of California-San Diego is the seventh oldest of the 10 University of California campuses and offers over 200 undergraduate and graduate degree programs, enrolling about 22,700 undergraduate and 6,300 graduate students. The University of California-San Diego is one of America’s Public Ivy universities, which recognizes top public research universities in the United States. The University of California-San Diego was ranked 8th among public universities and 37th among all universities in the United States, and rated the 18th Top World University by U.S. News & World Report’s 2015 rankings.