Recent trends in precipitation extremes in the Western US

Abstract

Seasonality is the strongest characteristics of the Western US hydroclimate, a region experiencing a Mediterranean type climate. With the recent shifts in the climate seasonality, Western US recently experienced severe summer and autumn droughts and wildfires, followed by flash floods. In contrast to this,  core winter months exhibit precipitation increase over the last few decades. Previous studies  that analyzed extreme precipitation along the West coast found slight increase in heavy precipitation events over southern and central coastal parts of California, and Washington state, and decrease in northern California and central Oregon coast. Considering different spatial patterns of precipitation extremes in the Western US at the annual and seasonal scale, in our research, we address spatial and temporal changes in precipitation extremes between 1960-2022 on monthly level. We particularly focus on differences in spatial pattern of precipitation extremes and their trends between the Northern (Oregon and Washington) and the Southern parts (California) of the Western US region. Finally, we ask what are the large-scale atmospheric conditions underpinning changes in precipitation extremes over the Western US. Both, extreme wet and dry precipitation events can have a significant influence on water resources and agriculture. A more detailed study of these events is critical for efficiently managing an already limited water supply in this region.