Hydro-Geochemical Conditions under Projected Climate Change Scenarios of Marshyangdi River, Nepal

Abstract

Assessment of hydro-geochemical processes in a Himalayan River fed by snow and glaciers in the context of global climate change is crucial to understanding the changes in water quality due to natural and anthropogenic influences. Thus, the hydro-geochemical status of water quality was analyzed in a snow-fed Himalayan Watershed, Marshyangdi located in western Nepal for current and future scenarios under the medium (RCP 4.5) and pessimistic (RCP 8.5) representative concentration pathways (RCPs) for two seasons (pre-and post-monsoon, 2019) based on multiple regional climate models. Flow at each sampling site of a total of twenty-one sites was estimated from a soil and water assessment tool (SWAT) hydrological model and then the concentration of water quality for the future was determined. A descriptive analysis of water quality was carried and a Piper plot diagram for evaluating the spatiotemporal variation as well as the hydro-geochemical status of water for the current and future scenarios. The results reveal alkaline water in the watershed based on pH values that follow the pattern of average ionic dominance Ca2+ > Mg2+ > Na+ > K+ for cations and HCO3− > Cl− > NO3− for anions indicating the carbonate-dominated lithology in the Marshyangdi Watershed for the current scenarios. However, for future scenarios dominance of cations is different for the respective seasons Ca2+> Na++K+ >Mg2+ and Na++K+ > Mg2+ > Ca2 with similar anion composition with respect to current scenarios under both RCPs.