Future Warming and Intensification of Precipitation Extremes: A “Double Whammy” Leading to Increasing Flood Risk in California

Abstract

This study focuses on quantifying future anthropogenic changes in surface runoff associated with extreme precipitation in California's Sierra Nevada. The method involves driving a land surface model with output from a high resolution regional atmospheric simulation of the most extreme atmospheric rivers (ARs). AR events were selected from an ensemble of global climate model simulations of historical and late 21st century climate under the “high‐emission” RCP8.5 scenario. Average precipitation during the future ARs increases by ~25% but a much lower proportion falls as snow. The resulting future runoff increase is dramatic—nearly 50%, reflecting both the precipitation increase and simultaneous conversion of snow to rain. The “double whammy” impact on runoff is largest in the 2,000–2,500 m elevation band, where the snowfall loss and precipitation increase are both especially large. This huge increase in runoff during the most extreme AR events could present major flood control challenges for the region.

Enhanced winter, spring, and summer hydroclimate variability across California from 1940 to 2019

“…In particular, California winter precipitation in the latter half of the 21st century is projected to be associated with less frequent, but wetter ARs at the expense of low to moderate precipitation from frontal storms (Gershunov et al ., 2019). These extreme precipitation events are expected to be 25% wetter with a sizable reduction in the amount of snow received at higher elevations across California’s Sierra Nevada (Huang et al ., 2020). Precipitation variability is further projected to increase by 10–25% from historical amounts throughout the state, especially in the south (Swain et al ., 2018; Gershunov et al ., 2019).…”

Connections Between Mean North Pacific Circulation and Western US Precipitation Extremes in a Warming Climate

“…We further examine precipitation changes near the WUS coast in the context of large-scale oceanic moisture flux changes, as moisture transport across the North Pacific is known to contribute substantially to precipitation in this region (Higgins et al, 2000;Lavers et al, 2016). As is the case for mean precipitation, precipitation extremes over the WUS coastal regions are driven by the large-scale moisture flux from the eastern North Pacific Ocean, mainly in the form of atmospheric rivers with substantial impact on the extreme rainfall events (Huang, Stevenson, et al, 2020;Leung & Qian, 2009;Nash et al, 2018;Ralph et al, 2004Ralph et al, , 2019. In this section, we aim to investigate the moisture flux changes, distributions, and uncertainties over the coastal regions during the wet season, and how that relates to the dynamical portion of future changes to precipitation.…”

Depth‐Duration‐Frequency of Extreme Precipitation Events Under Internal Climate Variability: Indian Summer Monsoon

“…We use the CESM‐LE (MICE) to quantify the internal variability by assuming that it captures all the variability such as Pacific decadal variability, Atlantic multidecadal variability, and interannual variability in tropical Pacific sea surface temperatures associated with the El Nio Southern Oscillation (ENSO) (Huang, Stevenson, & Hall, 2020). Such events largely influence the ISM extreme precipitation, which results in higher uncertainty.…”