Assessing the snow cover dynamics and its relationship with different hydro-climatic characteristics in Upper Ganges river basin and its sub-basins

Abstract

Snowmelt is an important source of water in upstream part of the Ganges river basin (GRB), which provides water for different purposes to its 655 million inhabitants. However, studies assessing relationship between snow cover dynamics and changes in hydro-climatic variables are limited within this region, motivating the current research. In this study, MODIS snow cover product (MOD10A1) was used to assess the snow cover area (SCA) dynamics within the Upper Ganges river basin (UGRB) and its sub-basins for the time period of 2002–2014; available climate and hydrological data were used to assess the hydrological characteristics within three selected sub-basins in Nepal; and relationships between snow cover and different hydro-climatic variables are established for three sub-basins owing to availability of hydro-climatic data. Results show that the average annual maximum SCA is around 24.6–47.5% for UGRB and its sub-basins. Upper Yamuna river basin (UYRB) with lowest mean elevation among the sub-basins shows a single SCA peak in spring within an annual cycle, whereas UGRB and the higher sub-basins show an additional lower peak in fall mainly resulted from snow sublimation. During 2002–2014, SCA shows slight decreasing trends for UGRB (Kendall's Tau τ = −0.039) and the higher elevation zones B (3001–4500 m a.s.l.) and C (>4500 m a.s.l.) of most sub-basins, with significance in Zone C of SaRB (τ = −0.070) and KoRB (τ = −0.062). Annual discharge for Gandaki river basin (GaRB) and Koshi river basin (KoRB) shows non-significant decreasing trends (τ = −0.182, −0.303) which are resulted from decreasing discharge in different seasons in different sub-basins. Seasonal correlation analysis indicates an important water supply from rainfall in GaRB and combined water supply from rainfall and snowmelt in KoRB, along with dominant contribution of precipitation in monsoon months and snowmelt in non-monsoon months for all the three sub-basins.