Hydrologic implications of aerosol deposition on snow in High Mountain Asia river basins

Abstract. The deposition of light-absorbing particles (LAPs) on snowpack is known to accelerate snowmelt. However, the resulting hydrological impacts, particularly on streamflow, remain under-explored. This study assesses the hydrologic consequences of LAP deposition on snow in High Mountain Asia (HMA) based on model simulations with and without aerosol deposition (“clean snow” scenario) during 2004–2018. We use the Community Land Model with a detailed aerosol-snowpack radiation module and the mizuRoute river model, driven by a 12-km meteorology-aerosol reanalysis dataset – the Model for Atmospheric Transport and Chemistry (MATCHA) – generated by the Weather Research and Forecast model coupled with Chemistry that assimilates satellite aerosol optical depth every three hours. The results show that LAPs advance seasonal snow cover disappearance by two weeks to over a month compared to the clean snow scenario. This shift alters both runoff and evapotranspiration (ET). LAP-deposited snow produces more runoff and ET until it is depleted; afterward, runoff declines due to earlier loss of snowmelt, while elevated ET persists even after LAP-deposited snow disappears as a darker, snow-free surface enhances evaporation from soil. Consequently, the annual runoff is slightly reduced under the LAP-deposited snow condition. Streamflow increases from late winter until snow melts completely but decreases due to earlier snow disappearance in LAP-deposited snow. This pattern is most evident in the headwaters, with the impact diminishing downstream. The semi-arid basins in the western HMA (e.g., Amu-Darya and Indus) show greater sensitivity to LAP deposition than the monsoon-dominated eastern HMA (e.g., Brahmaputra and Ganges). In western HMA regions, where larger perennial snow exists, LAP-enhanced snowmelt persists into summer and fall, leading to greater streamflow during these seasons compared to the clean snow scenario. This study provides important implications for the synergistic control of air pollution and water resource management.