Increasing heatwave frequency in streams and rivers of the United States

Abstract Heatwaves are increasing in frequency, duration, and intensity ocean, coastal, lake ecosystems. While positive water temperature trends have been documented many rivers, heatwaves not analyzed. This study examined rivers throughout the United States between 1996 2021. Riverine increased frequency over period, with most robust increases occurring summer fall, mid‐ to high‐order streams, at free‐flowing sites above a reservoir. The increase heatwave was accompanied by an moderate strength as well doubling of annual mean total number days site. were often associated normal or below‐normal discharge conditions ≤ 250 m 3 s −1 . These results provide first assessment for large geographic area States.