Suchana Acharya, Tomoharu Hori, Saroj Karki

The resources of the earth are under immense pressure due to the multiple anthropogenic influences. The land resources which largely attribute to the quality as well as quantity of the water, is facing extreme stress due to the rapid urbanization resulting from population growth as well as socio-economic development. It is imperative that the response of hydrological processes to the change in landuse is properly understood for the sustainable management of water and land resources. In view of the underlying problem of unscientific landuse practice as a result of the rapid urbanization and the consequent water-stress, this study has attempted to assess the spatio-temporal dynamics of the water-balance components in Kathmandu valley watershed from the past to the future. Forecasting the future landuse scenario and applying popular semi-distributed, physically based hydrological model Soil and Water Assessment Tool (SWAT), the change in water-balance component in the past, present and future scenario was evaluated. In order to exclusively quantify the impact of landuse change, the same climatic conditions are forced for all scenarios. Projection of landuse revealed that nearly half of the total area of Kathmandu valley watershed will be covered by built-up zone by the year 2040. The increase in the built-up area is compensated mainly by agriculture areas and the forest areas which will have further implications on the multiple ecosystem services. The results and analysis clearly indicated that the rapid urbanization will significantly alter the water-balance components of the study watershed that is already reeling under the water-stress. It was also concluded that the impact of landuse change on the water availability will be felt greater at the sub-basin level than at the basin level. The findings of this study entail the urgency to regulate the landuse practice as well as formulate appropriate measures to abate the adverse impacts.