Climate change is altering the timing, pace, and scale of the weather events that provide precipitation to California during the wet season from October through April. Historically, 90% of the annual precipitation shows up during this time with 50% showing up in the 3-month window from December through February. Snowpack is built up in the Sierra Nevada and Southern Cascade mountains from December through March, with a peak water content on or around April 1. Melting of the snowpack provides a key component of California’s water supply and typically occurs from April through July.
As the world warms, it is expected that in future decades, on average, there will be fewer but stronger storms during the wet season, a smaller snowpack limited to higher elevations, and warmer periods between storms that will act to dry out the landscape. The past decade has demonstrated that the historical patterns that are the foundation of current forecasting methods are already changing with new extremes (both wet and dry) that impact forecast quality using the methods that have been in place for decades.
Adapting to climate change requires changing the way we observe and forecast weather and hydrologic conditions. Historical patterns and relationships between precipitation, snowpack, and streamflow that have been used to anticipate how much water will run off for beneficial use have already shown vulnerabilities as illustrated in water year 2021. While DWR’s observation and forecasting programs have a long history of partnerships with the research community to bring relevant research advances into program operation, the pace and scale of extremes necessitate acceleration of recent and ongoing advances to ensure a forecasting framework that can adapt at the pace of a changing climate. This document provides a roadmap for a climate resilient forecasting framework (hereafter referred to as the Roadmap) to adapt to changing conditions.