The continuing shrinkage of snow cover in High Mountain Asia over the last four decades

High Mountain Asia (HMA), known as Earth’s “third pole” and “Asia’s water tower,” is the largest glacier and snow reservoir on Earth except for the polar ice sheets. Snow is an important component of the HMA cryosphere, and its variability directly affects the water and energy balances in the region. Identifying long-term changes in snow cover in the HMA region is important for the development of downstream water resources, prevention of water disasters, and survival and social stability of the “Third Pole” region.

We had developed a long-term, high-quality, daily High Mountain Asia Snow Cover (HMASCE) product to systematically study the snow cover indicators (SCA and snow cover phenology (SCP)) in different sub-regions and altitudes in HMA over the past 40 years in the context of global climate change. The results show that (1) the accuracy of the HMASCE product was validated using station snow depth data, with OA, PA, and UA values of 81.99%, 84.20%, and 76.39%, respectively. (2) the SCA shows a significant trend of shrinkage (-0.56% a^-1), snow cover days (SCD) shortens by 15.5 days, and snow cover start date (SOD) is delayed by about 5.6 daysand snow cover end date (SED) has advanced by 10 d in HMA over the last 40 years. (3) Another important finding is the altitudinal dependence of SCD, where, below 5000 m, higher altitudes experience lead to greater SCD reduction than lower altitudes. The possible mechanisms underlying this phenomenon related to the region's own characteristics, the elevation dependence of warming (EDW), and the increased black carbon.