Precipitation regime change in Western North America: The role of Atmospheric Rivers

Alexander Gershunov,David W Pierce,Rachel E S Clemesha,Michael D Dettinger,Suraj D Polade,Julie Kalansky,F Martin Ralph,Kristen Guirguis,Daniel R Cayan,David A Lavers,Tamara Shulgina

doi:10.1038/s41598-019-46169-w

Abstract

Daily precipitation in California has been projected to become less frequent even as precipitation extremes intensify, leading to uncertainty in the overall response to climate warming. Precipitation extremes are historically associated with Atmospheric Rivers (ARs). Sixteen global climate models are evaluated for realism in modeled historical AR behavior and contribution of the resulting daily precipitation to annual total precipitation over Western North America. The five most realistic models display consistent changes in future AR behavior, constraining the spread of the full ensemble. They, moreover, project increasing year-to-year variability of total annual precipitation, particularly over California, where change in total annual precipitation is not projected with confidence. Focusing on three representative river basins along the West Coast, we show that, while the decrease in precipitation frequency is mostly due to non-AR events, the increase in heavy and extreme precipitation is almost entirely due to ARs. This research demonstrates that examining meteorological causes of precipitation regime change can lead to better and more nuanced understanding of climate projections. It highlights the critical role of future changes in ARs to Western water resources, especially over California.

Highlights

We show that precipitation delivered by land-falling atmospheric rivers (ARs) along the West Coast will be enhanced by climate change, resulting in more frequent and stronger precipitation extremes even as the overall frequency of precipitation decreases due to fewer non-AR storms
The challenges faced by West Coast reservoir managers in balancing the mandates for water storage and flood control will escalate with an increasingly volatile precipitation regime
As ARs and their associated precipitation become more extreme, the need for improved predictions of AR activity on timescales ranging from days to seasons will grow in order to better manage the consequences of the changing climate

Summary

Other GCMs

The exercise of model validation with respect to the realism of simulated AR activity (Fig. S1) allowed us to constrain the range of GCM projections considered. In the Chehalis River basin (Fig. 2a), the projected increase in the frequency of dry days (

Russian River

Santa Ana River

Data and Methods

Author Contributions

Findings

Additional Information