Observed hydro-climatic trends and local perceptions of water availability: a mixed-methods study in Marsyandi river basin, Nepal

Sammanfattning: In the central Himalayas, water dynamics are expected to change due to multiple factors like climate change, hydro power development and shifting land use practices. This thesis looks at possible changes in water dynamics in Marsyandi river basin, Nepal, as well as causes to those changes and how they are perceived locally. Grounded in critical physical geography, the study uses mixed methods and an analytical approach of socio-hydrology. Trends in streamflow, precipitation and evapotranspiration from year 1998-2018 were analyzed using climate indices and the Regional Hydro-Ecological Simulation System, and local perceptions were explored through surveys and focus group discussions with households in a mid-hill village, Gaunshahar. The results indicate that the catchment’s average annual hydrograph peaks in August with variation in both peak timing within the monsoon season months and volume during the years of study. Evapotranspiration rates on the other hand, are highest in the pre-monsoon season according to the hydro-ecological model, which reaches a Nash-Sutcliffe efficiency of 0.51 against observed daily streamflow. Detected climate trends from 1998-2018 include a statistically significant increase in consecutive dry days (2 to 5 days/year), decrease in total precipitation (-26.1 mm/year) and increase in days above 25°C (2 days/year, all p-value >0.05). While the focus group participants highlight the importance of a new water pipe system which has increased the security of water supply, there are indications that the pipe system’s effectiveness varies within the village. The results prove that the local community has a high dependency on rainfall distribution and spring water availability rather than glacial or snow melt. In combination with the results of increasing temperatures and rainfall intensities over the time period the outcomes show that water availability has been more unpredictable over the course of the study period, but improved water infrastructure has simultaneously lowered the risk of water stress in the local community. For future studies, the Regional Hydro-Ecological Simulation System needs site-specific adjustments of model parameters but shows promising results for application in a Himalayan river basin. Social structures like caste and gender may be important aspects to consider for deepened understanding of the effects on water availability on a local scale.