Using the IHACRES model to investigate the impacts of changing climate on streamflow in a semi-arid basin in north-central Iran

Understanding the variations of streamflow of rivers is an important prerequisite for designing hydraulic structures as well as managing surface water resources in basins. An overview of the impact of climate change on the streamflow in the Hablehroud River, the main river of a semi-arid basin in north-central Iran, is provided. Using the LARS-WG statistical downscaling model, the outputs of HadCM3 general circulation model under the IPCC SRES A1B, A2, and B1 emission scenarios were downscaled to a finer spatial scale and the daily precipitation and temperature time series over the period of 2011-2030 for the study area were obtained. Results showed that the study area would experience a decline in precipitation (8.2% on average). The IHACRES rainfall-runoff model was then calibrated in the study area. Based on the fit statistics in calibration and validation phases, the overall performance of the developed model was judged to be satisfactory. The calibrated hydrological model was driven by the downscaled rainfall and air temperature data to project the effect of changing climate on the outflow of the basin under study. Results showed that, with some exceptions in June, July and August, all emission scenarios predict a decrease in the long-term monthly average outflow of the Hablehroud Basin. The outflow reduction in winter, spring, summer, and autumn had an average value of 25.7, 14.3, 1.9, and 48.8%, respectively. It was also observed that if climate change would occur in the basin, monthly flows associated to each return period would decrease.