Climate change decisive for Asia’s snow meltwater supply

Meltwater from seasonal snow provides a substantial amount of runoff to many of the rivers that originate in the high mountains of Asia, yet the importance of snow in the region as streamflow component, its changes over the past decades, and its sensitivity to future climatic changes are relatively unknown. To understand future changes in the water supply to the millions of people living downstream, a better understanding of snow dynamics at large scale is key. Using a novel snow model, forced by ERA5 climate reanalysis and calibrated by MODIS remote sensing observations, we generate daily snow water equivalent output at 0.05° resolution covering all major river basins in Asia. We show that between 1979 and 2018 significant and spatially variable changes have occurred in snow meltwater availability and its timing, with melt peaks attenuating and/or advancing in time, and snowmelt seasons shortening. Additionally, our results reveal that snowmelt is a much more important contributor to streamflow than glacier melt in many of Asia's large river basins. In a bottom-up elasticity analysis we project strong changes in snowmelt in the future under changing temperature and precipitation. Sensitivity of snowmelt to climate change varies among basins, however, and actual losses are strongly dependent on the degree of future climate change. Limiting climate change in the current century is therefore crucial in order to sustain the role of seasonal snow packs in Asia’s water supply.