Mechanism for Increasing Tropical Rainfall Unevenness With Global Warming

Abstract

Global climate models predict that tropical rainfall will be distributed more unevenly with global warming; that is, dry regions or months will get drier and wet regions or months will get wetter. Previous mechanisms such as “dry‐get‐drier, wet‐get‐wetter”; “rich‐get‐richer”; or “upped‐ante” focus on the spatial pattern of rainfall changes rather than the changes in probability distribution. Here, we present a quantitative explanation of the warming‐induced probability distribution change of rainfall: Subcloud moist static energy (MSE) gradients are amplified by Clausius‐Clapeyron relationship given roughly uniform warming and constant relative humidity. Therefore, the present‐day wet regions will become more competitive for convection in a warmer world. Though changes in the atmospheric circulation pattern can enhance rainfall in one place and suppress rainfall in another, our results show that the total effect should be a decrease in the area of active convection even with uniform warming.