Atmospheric water cycle over the Loess Plateau under the implementation of the Grain for Green project

Under the implementation of the Grain for Green project, a significant vegetation restoration trend has been observed on the Loess Plateau in recent decades, which has profoundly affected the regional water cycle. To investigate the effects of ecological restoration projects on the atmospheric water cycle, we analyzed the temporal and spatial variations in the key variables (including precipitation, evaporation, water vapor flux and its divergence, and precipitation recycling ratio) on the Loess Plateau during the 1991—2020 growing seasons, based on the MERRA-2 data and the moisture tracking model. The research has 3 results. ①From 1991 to 2020, both precipitation and evaporation showed significantly increasing trend over the Loess Plateau, and the trend in precipitation is higher than that of evaporation. ②Under an increasing precipitation trend, the precipitation resources on the Loess Plateau increased at approximately 0.352 × 10¹⁰ m³/a, with both external moisture sources and local evaporation exhibiting significant increases in absolute water vapor contribution. ③Although the increased precipitation primarily depends on additional contributions from external moisture source regions, the precipitation recycling ratio during the growing season over this region has increased significantly over the past 30 years due to the implementation of the GrainforGreen project, with an increasing rate of 0.0483%/a. This indicates that large-scale ecological restoration projects have exerted a positive effect on the regional atmospheric water cycle. The research findings of are of great significance for elucidating the driving mechanisms of large-scale ecological restoration projects on local hydrological processes and climate systems.