Assessment of Seasonal Surface Runoff under Climate and Land Use Change Scenarios for a Small Forested Watershed: Upper Tarlung Watershed (Romania)

This study aims to evaluate the potential impact of climate and land use change on seasonal dynamics of surface runoff within the Upper Tarlung watershed of 71.62 km(2). Using the Soil and Water Assessment Tool (SWAT), we simulated the surface runoff under the projections from four global and regional combination models for two representative concentration pathways (RCP4.5 and RCP8.5) and three land use change scenarios. In addition, short (2020-2039), mid (2040-2069), and long-term model simulations (2070-2100) were analyzed compared with a ten-year baseline period (1979-1988). Ensemble SWAT outputs showed that, in spring, surface runoff could decrease by up to 28% or increase by up to 86%, in summer can decrease by up to 69%, while in autumn and winter, increases of approximately two to five times fold are expected. The decreasing tendency is more pronounced under climate conditions, while the sharpest increases are estimated in the comprehensive scenario of climate and land use change by 50%. Those results serve as a support for local water, forest, and land managers in anticipating possible threats and conceiving adaptive strategies to manage the studied watershed efficiently.