Varied responses of inland waters to compound heatwave-drought events in the Yangtze River Basin

Extreme heatwaves and droughts are coinciding more frequently worldwide, exerting far reaching and adverse effects on ecosystems and economic development. Nevertheless, our knowledge of compound heatwave drought events (CHDEs) and their negative impacts on inland waters remains relatively scarce. Our findings indicate that the average annual duration of heatwaves varies: 3-107 days in river segments, 4-69 days in directly connected lakes, and 2-71 days in controlled lakes in the Yangtze River Basin (YRB), China's largest basin from 1980 to 2022. Significant linear increasing rates of heatwave frequency and duration are 1.49 events/decade and 16.21 days/decade in river segments, 0.98 events/decade and 7.85 days/decade in directly connected lakes, and 1.21 events/decade and 8.72 days/decade in controlled lakes. However, varied responses of different inland waters to droughts and CHDEs are observed with increasing frequency and duration in river segments and directly connected lakes. In 2022, the YRB witnessed an unprecedented extreme heatwave compounded by an equally exceptional drought. These changes pose significant challenges to aquatic ecosystems and economic development. Human interventions have demonstrated some effectiveness in alleviating droughts and CHDEs in controlled lakes. In contrast, river segments and directly connected lakes exhibited more frequent and longer droughts and CHDEs compared to controlled lakes. The repercussions of extreme CHDEs have been profound, combined with the regulation of the Three Gorges Dam, resulting in a sharp seasonal and annual shrinkage of directly connected lakes. Furthermore, CHDEs have exacerbated the precarious balance between hydroelectricity generation and electricity consumption, posing a direct threat to economic development. However, the increasing abilities in disaster management result in a notable reduction in economic loss although escalating extreme climatic and hydrological events.