Assessing the effect of climate and land use changes on the hydrologic regimes in the upstream of Tajan river basin using SWAT model

Climate change is the most important challenge in achieving sustainable development. Semi-arid and arid areas (such as Iran) are particularly susceptible to the effects of climate change on water supply. In this research, the effect of climate change and upstream land use is investigated on Tajan, a river in the north of Iran. The data regarding the climate were produced via second-generation Canadian Earth System Model (CanESM2) and adopted as the input to SWAT hydrologic model under RCP2.6 and RCP8.5 for the period of 2016–2066. The results showed that the peak streamflow will increase by 4% and 5.7% and the average annual discharges will decrease by 16% and 16.5% from 2016 to 2066 for RCP2.6 and RCP8.5 scenarios, respectively. Besides, the effect of different land use change scenarios on streamflow was investigated under four diverse scenarios selected to represent a comprehensive range of possible land use map of the basin. Land use change scenarios led to 8.5–15.8% increase in the average annual streamflow, highlighting the fact that it is less effective than climate change on streamflow. It could be concluded that downstream water users in the basin should adopt strategies to cope with water-stressed condition under the changing climate.