Widespread Increase in Atmospheric River Frequency and Impacts Over the 20th Century

Abstract Atmospheric rivers (ARs) play a dominant role in water resource availability in many regions, and can cause substantial hazards, including extreme precipitation, flooding, and moist heatwaves. Despite this, there is substantial uncertainty about recent and ongoing changes in AR frequency and impacts. Here, we place recent observed trends in their longer‐term context using AR records extending back to 1940. Our results show that AR frequency has increased broadly across the midlatitudes, bridging the apparent discrepancy between the observed satellite‐era poleward shift and the general increase simulated in climate change projections. This increase in AR frequency enhances AR‐associated precipitation and snowfall across their region of influence in the mid‐ and high‐latitudes. We also find that, despite warmer surface temperatures associated with ARs, there is a decrease in the magnitude of AR‐associated temperature anomalies in high‐latitude regions due to Arctic amplification. An increase in AR‐associated humid heatwaves underscores the societal importance of changing AR activity.