A Geographical approach of watershed prioritization in the Himalayas: a case study in the middle mountain district of Nepal

In recent decades, watersheds in the middle Himalayan belt have witnessed land degradation, flood, and landslide disasters. Growing population pressure, intensified use of watershed resources, and development activities—often alleged injudicious, have brought resource productivity and availability to the edge of unsustainability. The threat to precarious ecological balance, sustainable livelihood, and disaster risk is underpinning issues of densely populated Himalayan watersheds. Hence, understanding the essential physical characteristics of watersheds vis-à-vis human dimensions is essential for assessing and prioritizing the watersheds intended for ecological restoration, landslide and erosion control, and disaster risk reduction in upstream and downstream zones. Following these issues, this study using a geographical approach examines watershed variables representing susceptibility, hydrological and geomorphic response, land use, and human pressure to assess sub-watershed conditions and prioritize sub-watersheds. The study used high-resolution satellite imageries, digital elevation model, topographic and geological maps, rainfall and socioeconomic data from government sources to obtain the watershed variables. These variables were analyzed in the GIS platform. The leading variables and their relative importance were identified for assessing the watershed conditions by analyzing the correlation matrix, and AHP supported the expert judgment. These variables are mean basin slope, lineament density, drainage density, landslides, population density, and non-forest-forest ratio. The sub-watersheds condition of the Syangja District was assessed. The calculated overall vulnerability of sub-watersheds is positively related to susceptibility, poor land management, and human pressure index. The present study provided a methodological basis for assessing and prioritizing the watershed condition.