Divergent Seasonal Biophysical Effects Induced by the Three Gorges Reservoir

Large artificial reservoirs have been increasingly promoted over the last decades as an effective tool to relieve the shortage of water resources and mitigate the unavoidable negative effects of climate change. However, due to complex interactions between human and natural systems, their associated biophysical effects and the spatial extent of their propagation remain unclear. Here, we focus on the Three Gorges Reservoir (TGR), the world's largest hydropower project, to quantify its induced biophysical impact over the operational period 2010–2021 by integrating ground observations, satellite-based retrievals and process-based model simulations. Results show that the impoundment of TGR has led to a cooling at the local scale in daytime land surface temperature (LST) (−1.28 ± 0.05 K) particularly pronounced during hot and wet seasons and a warming signal in nighttime LST (+0.22 ± 0.06 K), markedly in cold and dry seasons. Such effects propagate toward surrounding territories up to 12 km far from the water body. Model simulations suggest that the widespread alteration in land-covers and water storage resulting from the TGR has influenced considerably the surface energy budget at regional scale both in terms of energy redistribution and radiative forcing ultimately leading to a net cooling. Such signal appears mostly driven by the increase in latent heat promoted by the enhanced water availability and changes in wind fields which ultimately offsets the opposite warming effect associated with the increased solar energy absorption resulting from the reduction in surface albedo. These findings underscore the role of reservoirs in regional climate change and offer strategic insights for large dam planning to mitigate emerging, warming-related, climate threats.