Synergistic effects of vegetation greening and irrigation on summer climate in the Sichuan Basin, China

Study region: Sichuan Basin, Southwestern China Study Focus: Intensive irrigation activity and vegetation greening have occurred in recent decades around the Sichuan Basin. This study investigated their effects and underlying mechanisms on the summer climate using WRF dynamic downscaling simulations from 2001 to 2020, incorporating real-time satellite vegetation data. New hydrogeological insights from the region: Results showed a significant expansion (p < 0.01) of summer Leaf Area Index (3.59 %/decade) and Fractional Vegetation Coverage (0.36 m²/m²/decade). Vegetation greening, irrigation, and their interaction significantly increased (p < 0.01) relative humidity (RH) by 0.460 %, 0.452 %, and 0.912 %, respectively, and produced notable cooling effects (p < 0.01) on daily mean temperature (T2avg) of −0.110°C, −0.085°C, and −0.195°C. Despite increased RH and enhanced moisture flux, no significant change in summer precipitation was simulated. Vegetation greening increased evapotranspiration, producing localized cooling, particularly in the western plains. Irrigation enhanced soil moisture, latent heat, and evapotranspiration (1.640 mm, p < 0.05), which reduced sensible heat and yielded widespread cooling across the basin. Their combined effects led to net cooling in the central basin, while albedo-induced warming was observed around the northern and southwestern edges, particularly in daily maximum temperature (T2max). Increased humidity elevated extreme wet-bulb temperatures in the western plains, whereas extreme Humidex values declined noticeably in the southwestern regions.