Atmospheric river precipitation drives rapid terrestrial water storage variability in the western United States

Using a decadal (2007-present) record of continuous GPS observations of Earth surface deformation, we estimate terrestrial water storage (TWS) across the western United States (WUSA) by inverting GPS displacements for associated water load changes. Throughout our record, we find large short-period (days to weeks) increases in winter TWS. In low-lying coastal regions, these increases in water storage are quickly lost through runoff into the ocean. By contrast, mountainous regions exhibit sustained winter TWS due to a combination of increases in snowpack, soil moisture, and surface water reservoirs. Using a published reanalysis-based catalog of ARs, we are able to ascribe these changes to landfalling atmospheric rivers (ARs) that deliver large quantities of precipitation over periods of hours to days. We find that the largest 5% of ARs (those classified as Category 5) delivered 400 Gt of water to the WUSA region between 2007 and 2017, an amount that represented 41% of water delivered from all ARs over this period. Given future expected increases in extreme precipitation events due to global warming, these geodetic estimates of water storage increases from ARs can provide valuable information on expected water availability in mountain watersheds and in discharge regions downslope. In California, we expect that changing frequencies of ARs will drive changes in the timing and magnitude of water influx into the agriculturally important Central Valley, and we demonstrate how these changes could occur using present-day patterns of ARs and associated runoff.