Recent shift in California’s precipitation distribution based on observations

Abstract Changes in precipitation in California are of great relevance to freshwater resource management, agriculture and food production, ecosystem health, wildfire risks, flood risks, and hydro-electric power generation. In this study, we use Parameter-elevation Regressions on Independent Slopes Model observational data to detect changes in California precipitation during 1981–2022. We report widespread drying after the late 1990s. The decline in mean annual precipitation between the first and last 20-year periods exceeds 100 mm yr −1 across more than 30% of California, with the largest losses concentrated in coastal regions, the Sierra Nevada, and northern California. The drying trend is obscured by large inter-annual variability and the occurrence of extreme precipitation events, especially during the wet season. The reduction in mean annual precipitation is accompanied by a decrease in precipitation variability and extreme precipitation events. The contribution of extreme precipitation events (top 8-percentile) to mean annual precipitation has decreased from 24% during 1982–2001 to 17% during 2002–2021. In contrast, extremely dry events (bottom 8-percentile) have increased modestly in several northern and central regions. A regression analysis indicates that large-scale circulation modes capture the spatial pattern of the observed drying trends during the analyzed period, even though they only explain ∼25% of the observed inter-annual variability in wet anomalies. These results indicate a gradual shift in California’s precipitation toward drier conditions and fewer extreme precipitation events in recent decades, which has implications for adaptation to drought, water resources management, and evaluation of hydroclimatic risks.