Snow cover variability and trend over the Hindu Kush Himalayan region using MODIS and SRTM data

Snow cover changes have a direct bearing on the regional and global energy and water cycles and the change in the Earth's climate conditions. We studied the relatively long-term (2000-2017) altitudinal spatiotemporal changes in the coverage of snow and glaciers in one of the world's largest mountainous regions, the Hindu Kush Himalayan (HKH) region, including Tibet, using remote sensing data (5gkm grid resolution) from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Terra satellite. This dataset provided a unique opportunity to study zonal and hypsographic changes in the intra-annual (accumulating season and melting season) and interannual variations in snow and glacial cover over the HKH region. The zonal and altitudinal (hypsographic) analyses were carried out for the melting season and accumulating season. The altitude-wise linear trend analysis (Pearson's) of snow cover, shown as a hypsographic curve, clearly indicates a major decline in snow cover (average of 5g% or more at 100gm interval aggregates) between 4000-4500 and 5500-6000gm altitudes, which is consistent with the median trend (Theil-Sen - TS) and the monotonic trend (Mann-Kendall - MK; statistics) analysis. This analysis also revealed the regions and altitudes where major and statistically significant increases (10g% to 30g%) or decreases (-10g% to -30g%) in snow cover are identified. The extrapolation of the altitude-wise linear trend shows that it may take between g1/4g74 and 7900 years, for 3001-6000 and 6000-7000gm altitude zones respectively, for mean snow cover to decline approximately 25g% in the HKH. More detailed analysis based on longer observational records and model simulations is warranted to better understand the underlying factors, processes, and feedbacks that affect the dynamic of snow cover in HKH. These preliminary results suggest a need for continued monitoring of this highly sensitive region to climate variability and change that depends on snow as a major source of freshwater for all human activities.