Global Assessment of Reservoir Impacts on Near-Surface Temperature

Large reservoirs have expanded rapidly worldwide over recent decades, substantially altering surface water distribution and land–atmosphere interactions. While reservoir-induced temperature effects have been documented at local and regional scales, their global characteristics and controlling factors remain poorly constrained. Using a dataset of 348 reservoirs and spatially consistent reanalysis data constrained by in situ observations (2001-2020), with elevation effects explicitly corrected, we quantified near-surface air temperature differences between reservoir-adjacent areas and surrounding reference regions. About 67% of reservoirs are associated with local cooling, particularly in arid and continental regions. Reservoirs reduce daytime extreme temperature by 0.14 °C on average and increase nighttime extreme temperature by 0.04 °C, showing a general pattern of daytime cooling and nighttime warming and narrowing the diurnal temperature range. Notably, the mitigating effect on extreme high temperatures has strengthened significantly over the 20-year period. Attribution analysis using mixed-effects modeling indicates that reservoir-induced thermal responses are primarily regulated by water body characteristics (area, capacity, regulation, and shape) and modulated by regional climate. These findings provide an observation-constrained global characterization of reservoir-induced temperature effects and highlight the role of large reservoirs in modifying land-atmosphere thermal interactions across diverse climatic settings.