Projection of surface air temperature and precipitation in High Mountain Asia and its major upstream river basins through multi-model ensemble from CMIP6

Future changes in temperature and precipitation over High Mountain Asia (HMA) and its major upstream basins are projected for the period 2025–2100 using eight selected Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6), with CN05.1 and ERA5-Land datasets serving as references. Projections derived from the Multi-Model Ensemble (MME) indicate a persistent warming trend, with rates of 0.1 (0.06–0.17) ℃·decade^-1 under SSP1-2.6, 0.3 (0.26–0.34) ℃·decade^-1 under SSP2-4.5, and 0.7 (0.61–0.80) ℃·decade^-1 under SSP5-8.5. By the mid-term period (2041–2060), the annual mean temperature over HMA is projected to reach 3.1 (2.4–3.8) ℃, 3.4 (2.7–4.0) ℃, and 3.9 (3.2–4.7) ℃ under the three scenarios, respectively. Winter exhibits the most pronounced temperature increase. High-warming areas are concentrated in the Tian Shan, the Pamir Mountains, the northwestern Himalayas, and the Bayan Kara Mountains. Among the upstream basins, the upper Yellow River generally exhibits the largest warming during the mid-term and long-term periods, while the upper Tarim and Ganges Rivers show relatively smaller warming. Precipitation also shows a distinct upward trend, with increasing rates of 0.8 (0.56–1.35) %·decade^-1 (SSP1-2.6), 1.2 (0.52–1.93) %·decade^-1 (SSP2-4.5), and 2.9 (1.49–4.73) %·decade^-1 (SSP5-8.5). By mid-term, projected precipitation amounts reach 574.5 (537.4–629.4) mm, 572.8 (528.2–634.3) mm, and 587.6 (521.8–649.2) mm under the three scenarios. Summer witnesses the most significant precipitation increase. Notable increases are projected over the western and central borders, the northern edges of the Tibetan Plateau, and the eastern Tian Shan. Among the upstream basins, the upper Ili River shows the largest precipitation increase, whereas the upper Amu Darya exhibits a slight decrease. These findings provide critical projections for water resource management and climate adaptation strategies in the HMA region.