Geophysical Research Letters | 2019
Contributions of Extreme and Non‐Extreme Precipitation to California Precipitation Seasonality Changes Under Warming
Abstract
Changes in seasonality of extreme precipitation have important implications for flood and fire hazards and water resources. Here we explore the contributions of extreme and non‐extreme precipitation in the sharpened wet season in California under warming and the underlying mechanisms. Modeling evidence shows that increased extreme precipitation due to enhanced extreme intensity and more extreme days dominates the wetter winter, while decreased non‐extreme precipitation due to fewer wet days induces the dryer spring and fall. Moisture budget analysis indicates that increased moisture dominates the extreme precipitation increase in winter, while weakened circulation offsets the moisture increase, resulting in no changes in spring and fall. The sharpened seasonal cycle of extreme precipitation via both dynamic and thermodynamic effects is consistent with the seasonality changes in atmospheric river days and is mainly attributed to the seasonality changes in the number of extreme days rather than the intensity during extreme days. Plain Language Summary There is an increasing demand for projections of precipitation changes under warming in California with a growing population and economy. Previous studies identified seasonality changes of mean precipitation showing a sharper winter peak but a shorter wet season in the future. Extreme precipitation may have more important societal and economic impacts, but potential changes in its seasonal cycle are unknown. Here we decomposed the total precipitation changes into extreme and non‐extreme components and found that increases in both extreme and non‐extreme precipitation contribute to the wetter winter, while decreases in non‐extreme precipitation dominate the dryer spring and fall. In particular, the increased extreme precipitation in winter comes from both enhanced intensity and frequency, while the decreased non‐extreme precipitation in spring and fall mainly comes from reduced frequency. Both dynamic and thermodynamic effects contribute to the sharpened wet season for extreme precipitation, consistent with the seasonality changes in atmospheric river days, which is the result of changes in seasonality of extreme days rather than the seasonality changes of circulation or moisture intensity during extreme precipitation days.