Assessment of Snow Persistency over Central Himalaya in Relation to Climate Variability

Snow covers a vast area of the Hindu Kush Himalayan (HKH) region, extending over ~18 % of the total area. Seasonal snow is a key component of the cryosphere in the HKH region and a major source of freshwater for sustaining the livelihood of more than one billion people. This study analyzes changes in annual snow persistency over Nepal in central Himalaya using an improved MODIS snow product (intersection of aqua and terra snow products) from 2003 to 2019 and the association with temperature and precipitation from ERA5-land reanalysis data. Annual snow persistency (SP) maps demonstrate significant variability in both space and time controlled by the interaction of topography and climate. The spatial distribution of annual SP trend over Nepal shows a heterogeneous pattern with a median value of 2 fewer days (with snow cover) per year. Average SP trends calculated for different elevation bands show negative values across all bands with the largest magnitude (3 fewer snow-cover days/year) between 4000 to 5000m where seasonal snow dominates. Precipitation and temperature data from ERA5-land reanalysis product showed a strong correlation (r>0.8) with gridded observed data (APHRODITE), Hence it is used to explore the relationship with annual SP. The study finds the SP to be positively correlated with precipitation in the mid and far western parts of Nepal whereas the relationship in central, and eastern regions was generally insignificant. However, annual mean temperature shows a negative correlation with SP for the whole country, such that a higher mean temperature leads to a lower snow persistency, as expected.