Has the Three Gorges Reservoir impacted regional moisture recycling?

Abstract

The Three Gorges Dam (TGD) and its impoundment significantly alter natural river properties and local land cover, drawing considerable concerns regarding its climatic and environmental effects. However, with the role of the Three Gorges Reservoir (TGR) in narrowing temperature ranges and changing precipitation patterns is well understood, its impact on moisture recycling is little known. Here, we tracked precipitation in the TGR basin back to evaporated moisture to explore the features of moisture recycling and quantify local evaporation ratios in the pre-dam (1980–2002) and post-dam (2003–2022) periods. The influences of the forcing data, simulation time steps and different tracking models on evaporation recycling are investigated. Relevant mechanisms are analyzed in terms of atmospheric motion, surface radiation, land cover changes and climate variability impacts. Results indicate that the precipitationshed shows a reduction in both summer and winter during the post-dam period. Local evaporation recycling ratios (ERRs) in TGR basin decrease by 0.46%, 1.07%, 0.59, 0.94% during the post-TGD period relative to the pre-TGD period in spring, summer, autumn and winter, respectively. Local evaporation contributions are limited in both the pre-dam and post-dam periods, especially in dry years. The reduced precipitation in TGR region is more dependent on upwind moisture, which results from the enhanced sinking motion and moisture divergence. Although different forcing data and simulation time steps show good agreement in spatial and temporal variations in the recycled moisture, the local ERRs are larger when calculated from the UTrack model than from the WAM-2layers model.