Regional drying over the Western U.S. driven by enhanced atmospheric subsidence amid global moistening from 1980 to 2020

Abstract

Abstract As the global climate has warmed anthropogenically over the past decades, the atmosphere across most of the globe has experienced significant moistening, except for a “moistening hole” (MH) -like change over the Western U.S. This regional anomaly since 1980 is at odds with the forced response of climate models to global warming in this region. Here, through analysis of a wide array of observations and water-tagging enabled simulations, we find that atmospheric forcing originating from the North Pacific contributes to the MH. A barotropic high-pressure circulation trend over the North Pacific, driven by observed sea surface temperature cooling in the tropical Eastern Pacific, enhances atmospheric sinking over the Western U.S. through equatorward cold air advection. This intensified atmospheric descent suppresses precipitation and weakens land-sourced evaporation, which are critical for replenishing atmospheric moisture in the region. We suggest that focusing on low-frequency changes of atmospheric vertical motion may offer insights into assessing and projecting climate stress and drought risks posed by long-term atmospheric moisture deficits in arid regions.