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. However, at regional scales, existing detection and attribution 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. Specifically, our results show that conflicting literature on trends in precipitation over the historical record can be explained by equal and (in many cases) opposite aerosol and greenhouse gas signals. At the scale of the United States, climate models reproduce observed behavior but cannot confidently determine whether these emissions sources increase or decrease rainfall.