Evaluating uncertainty in climate change impacts on peak discharge and flood volume in the Qaran Talar watershed, Iran

This study evaluates the effects of climate change (CC) on runoff properties over the case study of the Qaran Talar watershed located in Iran. To consider the two main sources of uncertainty on the subject of changing climate, i.e., greenhouse gases emission (GHG) scenarios and outputs of Atmosphere-Ocean General Circulation Models (AOGCMs), a daily rainfall time series was generated for two future periods (2021- 2050 and 2070-2099) at three risk levels of 0.1, 0.25 and 0.50. To this end, 22 AOGCMs outputs following two emission scenarios (RCP4.5 and RCP8.5) were used. The results showed that the uncertainty of CC scenarios was primarily owing to the uncertainty of GCMs outputs. Regarding the 2021-2050 period, under both emission scenarios, the increase in peak discharge (Q(peak)) and flood volume (FV) were estimated to reach 70, 50 and 30% at three risk levels of 0.1, 0.25 and 0.50, respectively. As the current century draws to a close, the difference between the results of the two emission scenarios becomes apparent so that in the 2070-2099 period, the RCP8.5 scenario estimates Q(peak) and FV more than the RCP4.5 scenario does. Additionally, it was found that the uncertainty caused by AOGCMs was more than that by GHG emission scenarios.