Future Changes in Snowpack, Snowmelt, and Runoff Potential Extremes Over North America.

Snowpack and snowmelt‐driven extreme events (e.g., floods) have large societal consequences including infrastructure failures. However, it is not well understood how projected changes in the snow‐related extremes differ across North America. Using dynamically downscaled regional climate model (RCM) simulations, we found that the magnitudes of extreme snow water equivalent, snowmelt, and runoff potential (RP; snowmelt plus precipitation) decrease by 72%, 73%, and 45%, respectively, over the continental United States and southern Canada but increase by up to 8%, 53%, and 41% in Alaska and northern Canada by the late 21st century. In California and the Pacific Northwest, there is a notable increase in extreme RP by 21% contrary to a decrease in snowmelt by 31% by the late century. These regions could be vulnerable to larger rain‐on‐snow floods in a warmer climate. Regions with a large variability among RCM ensembles are identified, which require further investigation to reduce the regional uncertainties. Plain Language Summary: Even though snow‐driven extreme events (e.g., snowmelt floods) have large societal impacts including infrastructure failures, how much future changes in the magnitude of snow‐driven extremes differ across North America is not well understood. Here, we found that the magnitudes of future extreme snow water equivalent (SWE) and snowmelt decrease over the continental United States and southern Canada but increase in Alaska and northern Canada by the late 21st century. In California and the Pacific Northwest, there is a notable increase in runoff potential (snowmelt plus precipitation) contrary to a decrease in snowmelt itself, suggesting that these regions may be vulnerable to larger rain‐on‐snow events in a warmer climate. Also, regions with a large variability among this study's regional climate models are identified. The large variabilities in extreme SWE and snowmelt in the western mountain regions and northern Canada as well as runoff potential in the southeastern United States require further investigation to reduce the regional uncertainties. Key Points: Extreme snow water equivalent (SWE), snowmelt, and runoff potential maps were developed using a regional climate model ensemble for historical and future periodsThe magnitudes of projected extreme SWE and snowmelt decrease over the CONUS and southern Canada but increase in Alaska and northern CanadaThere is a projected decrease in snowmelt but an increase in runoff potential (e.g., rain‐on‐snow) in California and the Pacific Northwest [ABSTRACT FROM AUTHOR]