Exacerbating hydrological extremes in China’s large reservoir drainage areas

Abstract

Reservoirs are vital infrastructure for mitigating hydrological extremes, providing water during droughts, and reducing risks associated with floods. Under a warming climate, increasing hydrological extremes in upstream catchments threaten water supply sustainability and dam security. However, the evolution and drivers of these extremes are still poorly understood due to limited precise drainage boundary data. To address this gap, we combine a delineation algorithm with manual adjustments according to recorded drainage areas, creating the most comprehensive publicly available inventory of 907 large Chinese reservoirs, each with a storage capacity exceeding 0.1 km³. By integrating delineated boundaries with an observation-based China natural runoff dataset, we find nearly 40 % of reservoirs face more intense and frequent droughts, jeopardizing their role in supporting regional water transfer projects. Additionally, nearly 60 % experience worsening pluvial conditions, putting reservoirs in the northwest, northeast, and lower Yangtze regions under flood control and coordination pressures. These intensifying hydrological extremes strongly correlate with climate variability modes, while their variations are further influenced by climate change, widespread greening, and other external factors. Given reservoirs’ essential role in human water use, this study highlights the urgent need to understand the effects of climate and landscape changes to advance sustainable water resource management and safeguard water security.