Runoff and sediment dynamics induced by the “grain for green” programme: A case study in the Three Gorges Reservoir Area, China

In the context of climate change, large-scale vegetation restoration projects have significantly altered hydrological processes. However, existing studies have primarily focused on the impact of the “Grain for Green” programme (GGP) on hydrological dynamics in arid areas, neglecting humid regions. To help close this gap, we simulated streamflow and sediment yield in the Three Gorges Reservoir Area (TGRA), an important ecological zone in China, using the SWAT + model. We differentiated the effects of the GGP and climate change on streamflow and sediment yield in different hydrological periods. The results show that sediment yield responds more intensely to variations in vegetation composition compared to water yield. From 2000 to 2020, reforestation has significantly reduced annual sediment yield by an average of 802.6 kg/ha. Climate change was identified as the main driver of the changes in runoff and sediment yield. Furthermore, the effects of reforestation exhibit seasonality, with runoff increasing during the dry season and sediment yield decreasing during the flood season. The GGP also reduces runoff and sediment yield extremes and promotes the stability of the water-sediment relationship. In addition, projections of future climate scenarios from 2025 to 2050 indicate an upward trend in total runoff and a downward trend in soil retention. This study provides insights into the impacts of the GGP and climate change on hydrological processes in humid regions and offers guidance for future development pathways.