Understanding the Role of Snowmelt Processes on Soil Moisture Storage and Vegetation Dynamics acrossTopographic Gradients of Himalayan Catchments

Seasonal snowmelt strongly influences hydrological and ecological processes by controlling the timing of peak soil moisture and subsequent vegetation growth; yet, this relationship is less studied in the Indian Himalayan region, especially in Himachal Pradesh’s snow region. This study investigates the linkage between snow disappearance timing and peak soil moisture using station data across various elevation ranges from 1571 m to 3325 m and the FLDAS dataset (daily, 0.01° resolution), and then their effect on vegetation growth using the MODIS NDVI product (8-day, 250-m resolution). We quantified the spatial and temporal variability in snow recession by fitting an exponential decay model. The recession rate varies between 0.03 and 0.27 across various elevation ranges and temporal periods. The recession rate also exhibits a strong elevation dependency, being low at higher elevations (e.g., Lari, 3325 m m.s.l., k = 0.044 m/day) and high at lower elevations (e.g., Dodra Kawar, 2522 m m.s.l., k = 0.169 m/day). Based on analysis from 2001 to 2020 across nine stations, results show that snow onset occurs in mid-December, followed by snow recession in late February and complete snow disappearance by late March across Himachal Pradesh. We observed an average lag of 3-4 days between the timing of peak soil moisture and snow disappearance, and a correlation of 0.94 (p < 0.05) was observed across various stations. Early melt does contribute to greening, as evidenced by the weaker but still positive correlation (0.54, p < 0.05) between the timing of snow disappearance and the rise in NDVI. The results show that the timing of snowmelt primarily influences soil moisture dynamics and controls vegetation activity in Himalayan catchments.