Influences of Desert Afforestation on Boundary Layer Convergence Lines and Related Convection and Convective Precipitation Over Desert-oasis Border

Land use and Land cover changes significantly influence weather and climate by altering surface albedo, roughness, heat flux, and boundary layer dynamics. These changes can modify convection and precipitation through shifts in near-surface temperature, moisture, and atmospheric instability. Vegetation heterogeneity across a desert-oasis divide has been observed to generate boundary layer convergence lines (BLCLs) and initiate convection. Afforestation may affect these behaviors through land-air interaction and boundary layer processes. Since 1986, the Hetao area of the Yellow River in north China, where an irrigated oasis is surrounded by extensive deserts, has undergone afforestation for over 30 years. This study examines how this desert afforestation may affect BLCLs and their associated convection and precipitation through ensemble simulation by perturbing a composite of 34 cases in the synoptic pattern that has the most frequent formation of BLCLs and their associated convection initiation (CI). The results indicate that the afforestation weakens the desert-oasis contrast in 2-m air temperature and moisture, causing BLCLs to form later, attain maximum length later, and weaken. Although delaying and weakening convective triggering, the afforestation increases the near-surface water vapor content and vertical transport of water vapor, and thus the resultant larger instability, which accelerates CI, intensifies and spatially broadens convection, and causes more frequent and heavier convective precipitation in Hetao area. This study suggests that afforestation can enhance convection and precipitation at the desert-oasis boundary even though it seems to do the opposite by delaying and weakening convection triggers. These findings have important implications for weather forecasting, land management, and climate adaptation in arid and semi-arid regions.