Observational Evidences in the Effects of Large-Scale Reforestation on Precipitation

Reforestation is widely recognized for its potentials to enhance downwind precipitation. However, this claim is largely based on climate models or estimates derived from global water budgets. Given the significance of this subject, scientific communities repeatedly call for observational evidences to validate this claim. In this study, we select China's Loess Plateau (LP) as a representative region for large-scale reforestation, with vegetation cover increasing from 32% in 1999 to 64% in 2019, to statistically test its effects on downwind precipitation. Using satellite-derived forest data and precipitation observations from 274 ground stations, combined with simulated moisture transport trajectories from FLEXPART-WRF, we apply nonparametric trend tests and correlation analyses to assess the impact of reforestation on precipitation. The results reveal a significantly positive LAI-precipitation relation in LP during the growing season, particularly in the northeastern part of the region, highlighting the role of reforestation in increasing regional precipitation. The non-growing season has little impact on identifying the correlation. We further analyze the potential driving factors and mechanisms behind the observed patterns. No significant effects are detected beyond LP region. This study provides statistical evidences on the influence of reforestation on downwind precipitation. Some uncertainties are also discussed.