Linkages between atmospheric rivers and humid heat across the United States

The global increase in atmospheric water vapor due to climate change tends to heighten the dangers associ- ated with both humid heat and heavy precipitation. Process- linked connections between these two extremes, particularly those which cause them to occur close together in space or time, are of special concern for impacts. Here we investigate how atmospheric rivers relate to the risk of summertime hu- mid heat in the United States. We find that the hazards of atmospheric rivers and humid heat often occur in close prox- imity, most notably across the northern third of the United States. In this region, high levels of water vapor – result- ing from the spatially organized horizontal moisture plumes that characterize atmospheric rivers – act to amplify humid heat, generally during the transition from dry high-pressure ridge conditions to wet low-pressure trough conditions. In contrast, the US Southeast, Southwest, and Northwest tend to experience atmospheric rivers and humid heat separately, representing an important negative correlation of joint risk.