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Did you know that roughly half of California’s annual precipitation and over 90-percent of its flood damages are caused by a phenomenon known as

atmospheric rivers?

ARs, as they are commonly known, are focused channels of moisture in the atmosphere that can carry the equivalent of 25 Mississippi Rivers’ worth of water within individual storm systems. Accurately forecasting ARs to strengthen our resilience to climate change is the central goal of California scientists, federal and state agencies, and regional water districts.

Sonoma Water, scientists at UC San Diego’s Scripps Institution of Oceanography, California Department of Water Resources, and the U.S. Army Corps of Engineers have pioneered a program called forecast-informed reservoir operations, or FIRO for short. FIRO enables water resource managers to optimize how much water is stored in California reservoirs by incorporating AR forecasts into operational decision making. This approach allows water agencies to enhance their water supply while also mitigating flood risks during the rainy season. In 2021, FIRO enabled Sonoma County to store an additional 11,000 acre feet, a nearly 20-percent increase, in Lake Mendocino that otherwise would have been required to be released under existing regulations. 

Improved AR forecasts also provide the data needed for the National Weather Service to create hazard weather forecasts alerting residents and emergency managers of dangerous mudslides and post-wildfire debris flows within burn zones. Forecast-based decisions also support groundwater recharge efforts, renewable energy generation, and biodiversity conservation goals. 

A statewide coalition water agencies and stakeholders, including CSDA, are pursuing a $10 million budget request to the State of California to ensure continued AR forecast improvement and FIRO implementation at additional reservoirs. The Governor’s May Revise includes $10m in ongoing funding to expand FIRO and support AR forecast development. For more information about the coalition and its efforts, please contact Ian Clampett with UC San Diego’s Scripps Institution of Oceanography at iclampett@ucsd.edu.

The $10 million proposal for AR forecasting and FIRO implementation is included in the 2022 Key Budget Requests CSDA is supporting in the State Budget process. Legislators must pass a balanced budget by the Constitutional deadline of June 15.

To learn more about AR and advanced precipitation quantification information radar systems, watch this CSDA video featuring Sonoma Water and Santa Clara Valley Water District. For more information about Scripps atmospheric rivers research, please visit the Center for Western Weather and Water Extremes (CW3E) website. CW3E at Scripps is the world’s leading center for research on atmospheric rivers. Its aims are to improve scientists’ abilities to characterize ARs, predict if, when and where they will originate and make landfall, and how intense they will be. A scale created by CW3E scientists works similarly to scales measuring wind or hurricane strength and helps emergency officials distinguish between largely beneficial ARs and those with the potential to cause severe flooding and property damage.