Elevation-Dependent Trends in Himalayan Snow Cover (2004–2024) Based on MODIS Terra Observations

Snow cover in the Himalayas plays a vital role in regulating elevation-dependent climate processes and sustaining downstream hydrology. However, its altitude-specific dynamics and implications for snow mass balance remain underexplored. Using the MOD09A1 dataset (2004–2024), this study conducts a pixel-based, elevation-stratified analysis with advanced spectral filtering and gap-filling techniques to enhance snow cover detection in complex terrain. The mean SCA was ~2.10 × 105 km2, with sub-regional contributions from WH: 8.59 × 104 km2, CH: 9.55 × 104 km2, and EH: 2.99 × 104 km2, indicating distinct spatiotemporal variability. Correlation analysis revealed that SCA in WH and CH is mainly precipitation-driven (r = +0.70 and r = +0.91), whereas EH is temperature-dominant (r = −0.65), reflecting strong climatic control. Altitudinal and zonal snow cover changes were assessed using Equilibrium Line Altitude–AAR and AABR methods for mass balance estimation. Regional trends showed a positive mass balance of 0.0389 at 4105 m in WH, with increasing SCA around 4516.12 ± 531.94 m; CH exhibited a negative balance (−0.0268 at 4989 m), with declines at higher altitudes; and EH demonstrated a negative balance (−0.015 at 4378 m), with notable SCA reduction. Mann–Kendall and Kendall Tau tests validated these trends, highlighting spatially heterogeneous snow-cover dynamics and their implications for Himalayan snow-mass balance.