Anthropogenic aerosols mask increases in US rainfall by greenhouse gases

Abstract Daily rainfall accumulations are a critical component of the global water cycle, and comprehensive understanding of human-induced changes to rainfall is essential for water resource management and infrastructure design. Detection and attribution methods reveal cause and effect relationships between anthropogenic forcings and changes in daily precipitation by comparing observed changes with those from climate models. However, at regional scales, existing studies are unable to conclusively identify human influence on precipitation. Here we show that anthropogenic aerosol and greenhouse gas emissions are the dominant drivers of precipitation change over the United States and, by simultaneously accounting for both agents, we resolve outstanding uncertainties regarding the human influence on regional precipitation. Greenhouse gas emissions increase mean and extreme precipitation from rain gauge measurements across all seasons. Aerosol emissions offset these increases in the winter and spring but appear to enhance rainfall during the summer and fall. Our results show that conflicting literature on trends in precipitation over the historical record can be explained by equal and opposite aerosol and greenhouse gas signals. At the scale of the United States, individual climate models reproduce observed changes due to anthropogenic forcing but cannot confidently determine whether these emissions sources increase or decrease rainfall.