Projected Changes to Extreme Precipitation Along North American West Coast From the CESM Large Ensemble

Weiming Ma, Jesse Norris and Gang Chen

Abstract

Precipitation events along the North American (NA) west coast are strongly modulated by atmospheric rivers, yet the mechanisms of their influences on the probability distributions of precipitation events are not well studied. Simulations from the Community Earth System Model (CESM) large ensemble under global warming are investigated using a moisture budget conditioned onto precipitation events for the recurrence intervals ranging from 0.1 to 50 years. In the midlatitudes, the increases in precipitation intensity and accumulation for all events over the NA west coast are predominantly controlled by moisture increases. In contrast, changes in the subtropical precipitation distributions in southwestern NA are associated with moisture increases and duration decreases for all events, with additional dynamical amplification for the heaviest precipitation events. These interpretations from the conditional moisture budget are more consistent with future projection of atmospheric rivers than the conventional mean and transient decomposition of the moisture budget.

Gang Chen

Professor, Dept. of Atmospheric and Oceanic Sciences, University of California, Los Angeles

Math Sci Building 7149, Los Angeles, CA 90095

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Projected Changes to Extreme Precipitation Along North American West Coast From the CESM Large Ensemble

Published in Geophysical Research Letters, 2020

Recommended citation: Weiming Ma, Jesse Norris and Gang Chen, 2020: Projected Changes to Extreme Precipitation Along North American West Coast From the CESM Large Ensemble, Geophysical Research Letters, 47, 1–10, doi:10.1029/2019GL086038.

Abstract

Precipitation events along the North American (NA) west coast are strongly modulated by atmospheric rivers, yet the mechanisms of their influences on the probability distributions of precipitation events are not well studied. Simulations from the Community Earth System Model (CESM) large ensemble under global warming are investigated using a moisture budget conditioned onto precipitation events for the recurrence intervals ranging from 0.1 to 50 years. In the midlatitudes, the increases in precipitation intensity and accumulation for all events over the NA west coast are predominantly controlled by moisture increases. In contrast, changes in the subtropical precipitation distributions in southwestern NA are associated with moisture increases and duration decreases for all events, with additional dynamical amplification for the heaviest precipitation events. These interpretations from the conditional moisture budget are more consistent with future projection of atmospheric rivers than the conventional mean and transient decomposition of the moisture budget.

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