Scripps Scientist Keynotes Meeting of State Water Managers

Extreme weather expert address a nod to increasing value of precipitation forecasts in reservoir operations

F. Martin Ralph, a researcher at Scripps Institution of Oceanography at the University of California San Diego, laid out the progress the science community has made in creating information that has the potential to support more flexible reservoir operations to the Association of California Water Agencies on Nov. 30.

At the association’s fall conference in Anaheim, Calif., Ralph briefed water managers from throughout California on the science of atmospheric rivers, channels of moisture in the atmosphere that can deliver large amounts of rain and snow in a matter of days. In places like California, these episodic events can deliver half a region’s annual water supply during the course of several winter storms. Ralph leads a community of scientists using the understanding of these phenomena to update thinking on how reservoirs throughout the state might operate more flexibly.  He works closely with the Sonoma County Water Agency (SCWA), California Department of Water Resources, U.S. Army Corps of Engineers, NOAA, and many others to pursue these problems.

“We now understand that atmospheric rivers are the key to California’s water supply, and are working with water managers, flood control experts, and others to explore how better predictions of atmospheric rivers could enable both enhanced water supply reliability and flood mitigation,” Ralph told an audience of several hundred people.

The address capped a year of collaboration between Scripps researchers and state officials on water issues, one that began with an El Niño winter that did little to lift the state out of a historic drought. In June, California Gov. Jerry Brown authorized the allocation of funds that will create a program proposed by a Northern California water agency that drew on science largely developed by Ralph and Scripps colleagues.

Earlier in November, Scripps Oceanography hosted with the California Department of Water Resources a workshop on improving seasonal precipitation forecasting, an area of research state water managers hope to make a greater collaborative priority among climate scientists and officials. The meeting highlighted advances in atmospheric river understanding and predictive tools, and the need for innovative approaches to be developed to advance forecast skill. 

Ralph leads a branch of science barely in existence 20 years ago. Strong atmospheric rivers can move an amount of water vapor equivalent to about 20 times the average flow of liquid water at the mouth of the Mississippi River. Based on advances in modeling in the early 1990s, scientists first coined the term “atmospheric river” to describe the key role of this phenomena in the global water vapor budget.  However, it wasn’t until a study by Ralph in 2004 that brought new satellite and research aircraft data to the subject, and documented the key role in precipitation that study blossomed.  Since then, specialized satellite observations have enabled scientists to detect and characterize atmospheric river conditions. With support from NOAA and the U.S. Navy, among others, Ralph has led development of atmospheric river observatories on the West Coast to provide complementary ground-based data. Forecasters are now able to develop short-term predictions of precipitation based on present knowledge, but observation must continue over the long term to improve forecast capabilities.

In 2013, Ralph joined the Scripps Oceanography faculty and created the Center for Western Weather and Water Extremes at Scripps.

The Atmospheric Rivers: Research, Mitigation, and Climate Forecasting Program funded by Brown this summer could enable greater water supply reliability for reservoirs than is possible now. Researchers hope it will provide potent new information to support modern reservoir operations strategies now under development by the U.S. Army Corps of Engineers and other entities.

The program was authorized in 2014 with passage of Senate Bill 758 authored by 39th District State Senator Marty Block, and funded in 2015 with support from Senate President Pro Tem Kevin de Leon, Senate Speaker Anthony Rendon, and Assembly Budget Chair Philip Ting. The program could enable better forecasts of atmospheric rivers and retooling of operations at Lake Mendocino near Ukiah, for example, where SCWA officials estimated that such measures could increase available water supply from the lake 10 to 20 percent.

–      Robert Monroe

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