Anthropogenic aerosols contribute to the recent decline in precipitation over the U.S. Southwest

Abstract

A significant decline of precipitation over the Southwestern United States (SWUS) has been observed since 1980. To investigate the causes behind this decline, we determine the relative contributions of internal decadal variability in Pacific Sea Surface Temperatures (SSTs) and anthropogenic forcings. Applying a low frequency component analysis (LFCA) and multivariate linear regressions to observations and a set of counterfactual climate model experiments with CESM2, we find up to 22% of the observed SWUS precipitation trend can potentially be attributed to anthropogenic aerosol (AA) induced SST changes. Other radiative forcings counteract this influence, leading to a relatively weak net forced response in SWUS precipitation in CESM2. Our results imply that the near-future emission trajectories of these forcings, in particular aerosols, are important for making projections of SWUS precipitation.