Climatic effects of afforestation over the middle-upper reaches of the yellow river

Afforestation is an important human activity that changes land use, and would affect regional climate. However, the impact of afforestation on the regional climate in arid and semi-arid regions remains a subject of controversy. By ensemble sensitivity simulations using Advanced Research Weather Research and Forecasting (WRF) model, this study investigates the influence of vegetation category change within a 100 km width along the middle and upper reaches of the Yellow River (YR) on regional climate. Results suggest that afforestation would reduce summer surface temperature by -0.05 ~ -0.8℃ and increase summer convective precipitation by 3 ~ 45 mm in the afforestation regions, instead, summer non-convective precipitation would increase (3 ~ 35 mm) in the upper reaches of the YR. The increased non-convective precipitation in the upper reaches of the YR could be attributed to the increased integral water vapor convergence, cloud hydrometeor, and decreased cloud top temperature. In the afforested region, the increased convective precipitation could be related to the enhanced thermodynamic and water vapor conditions. These findings emphasize that even on regional scale in semi-arid and arid regions, greening can lead to evident regional climate impacts, these also provide insight for policymakers in formulating sustainable afforestation strategies.