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Publication Date
1 September 2017

The Changing Character of Twenty-First-Century Precipitation over the Western United States in the Variable-Resolution CESM



The changing characters of precipitation frequency and intensity have been comprehensively investigated from recent historical period to the end of the 21st century over the western United States. Variable-resolution Community Earth System Model (VR-CESM) ensemble simulations are applied with a fine grid resolution of ~0.25 degrees over the study area. Simulations are forced with prescribed sea-surface temperatures, sea-ice extent and greenhouse gas concentrations from the representative concentration pathway (RCP) 8.5 scenario. VR-CESM is shown to be effective at accurately capturing the spatial patterns of the historical precipitation climatology. The results of VR-CESM output provide significantly regional details with crucial enhancement of precipitation representations over complex terrain. In the Intermountain West and Southwest U.S., we observe a statistically significant increase in mean precipitation and rainy days through mid-century, although this trend is tampered by end of the century in response to a decrease in relative humidity. Over the Pacific Northwest, extreme precipitation events are observed to increase significantly as a result of increased cool-season integrated vapor transport associated with a moistening of the cool seasons and drying through the warm seasons. In particular, extreme precipitation in this region appears to increase more rapidly than would be predicted by the Clausius-Clapeyron relationship. No clear climate signal emerges in mean precipitation or extreme events in the majority of California, where the precipitation climatology is attributed with large interannual variabilities that are tied closely to ENSO patterns.

“The Changing Character Of Twenty-First-Century Precipitation Over The Western United States In The Variable-Resolution Cesm”. 2017. Journal Of Climate 30: 7555-7575. doi:10.1175/jcli-d-16-0673.1.
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