Quantifying the impact of large-scale afforestation on the atmospheric water cycle during rainy season over the Chinese Loess Plateau

Afforestation is an efficient measure to mitigating climate change and achieving carbon neutrality. However, there is a growing concern regarding the impact of afforestation on water resource availability owing to the water consumption through evapotranspiration (ET). The Loess Plateau (LP) in China has implemented the largest afforestation program in the world, the Grain for Green Program (GFGP), to curtail severe soil erosion. However, the effects of large-scale afforestation on the atmospheric branch of the hydrological cycle (i.e., the atmospheric water cycle (AWC)) are poorly understood. Combining a regional climate model and an analytical precipitation recycling model, this study quantitatively investigated the responses of precipitation recycling and components of the atmospheric water cycle to the GFGP over the LP during the rainy season. Two long-term simulations with high resolution were conducted for the LP's regional climate under two scenarios: with and without the implementation of the GFGP. Results show that the GFGP intensified the AWC and increased the precipitation and atmospheric water vapor. The GFGP enhanced the ET and precipitation recycling ratio of the internal branch of the AWC, which contributed 15.51% of the increased precipitation. Meanwhile, the contri-bution of the external branch was 84.49%. In addition, both the inflow and outflow moisture fluxes showed increases induced by the GFGP; the inflow was larger than the outflow, leading to more moisture being retained on the LP. Moreover, the enhanced ET reinforced surface diabatic heating and caused an abnormal cyclone, resulting in more moisture being advected from the southern boundary, which can partly counteract the weakening East Asian summer monsoon. Furthermore, the GFGP has remotely strengthened the water vapor advection being received by downwind areas. This work advances the current understanding of the way large-scale afforestation affects the hydrological cycle from the viewpoint of the AWC, and can help direct future afforestation plans towards science-informed carbon neutrality and sustainable ecosystem management.