Divergent and Changing Importance of Glaciers and Snow as Natural Water Reservoirs in the Eastern and Southern Tibetan Plateau

Glaciers and snow are natural water reservoirs in the Tibetan Plateau (TP), affecting ecosystems, water and food security, and more than one billion downstream people. Meltwater volumes are traditionally estimated using the degree-day concept considering only air temperature, which cannot consider the influence from downward solar and longwave radiation, humidity, wind and resultant turbulent heat fluxes. Here, we used a physically based energy budget approach considering the full energy balance in seven large river basins in the eastern and southern TP. For 1982–2011, the estimated average glacier melt was 0.32 ± 0.007 m water equivalent/yr with large spatial variability. Air temperature, downward longwave radiation, humidity, and wind speed influenced the overall glacier melt trend, and glacier melt accelerated with a rate of 0.42 mm/yr. Yet, downward shortwave radiation played an additional role in influencing the glacier melt rate fluctuation. On average, snow and glacier melt contributed 17.6% of annual river discharge during 1982–2011, including 10.0% from snow and 7.6% from glaciers. The highest and lowest relative melt contributions were in the Yarlung Tsangpo and Yalong Rivers, respectively. Mainly due to decreasing snow melt, glacier and snow melt contributions to discharge would decrease to 11.9% during 2021–2050 under the extreme climate scenario (RCP8.5), and the greatest change in the relative contributions would occur in the Upper Nu River (−9.2%). These findings indicate the divergent and changing importance of glaciers and snow as natural water reservoirs, potentially affecting socioeconomic development and adaptation to climate change in South, Southeast, and East Asia.