Investigating the effect of climate change based on different scenarios on the runoff and inflow to Nahand dam reservoir

Background and Objectives
Global warming is one of the challenges that has attracted more and more public opinion in recent years, and if wrong behavior continues, including excessive use of fossil fuels, it can become a serious threat to human life. One of the effects of global warming is climate change. The phenomenon of global warming and the resulting climate change, with changes in temperature and precipitation, have significant effects on various systems such as water resources, agriculture, and the environment. In such a way that it can be considered as a big threat to water systems all over the world. These threats are different for different regions of the world. The industrialization of societies and increasing greenhouse gases have caused climate change and seriously threaten human life. Change in rainfall is one of the important effects of climate change. Changes in precipitation have affected surface runoff and underground water sources, and in such conditions, water resources management becomes more difficult and complicated. The most reliable tool for investigating the effects of climate change on different systems is the use of climate variables simulated by coupled atmosphere-ocean general circulation models. These models can simulate climate parameters (temperature, precipitation, etc.) for future periods. But the main weakness of these models is their low spatial resolution and the simplifications they consider for climate processes. Microscale exponentials are used to cover the weakness of spatial resolution. The aim of this research is to evaluate the climate change on temperature and precipitation and its effect on the runoff entering the Nahand dam reservoir.

Methodology
In this research, the daily temperature and precipitation data of Nahand basin during the period (1360-1384) were used as the base period to evaluate climate changes using the CanESM2 climate model and RCPs emission scenarios in future periods. And SDSM statistical model was used for the microscopic scale.By applying the output of the CanESM2 general circulation model, using the SDSM model under RCP 2.6, RCP 4.5 and RCP 8.5 emission scenarios, and with the help of the IHACRES conceptual integrated model, the impact of climate change on the runoff entering Nahand Dam was evaluated.Nahand Dam is one of the drinking water sources of Tabriz. Therefore, determining the incoming runoff to the tank can help to manage the system optimally. Also, to simulate the runoff entering the reservoir in future periods, the conceptual integrated model of IHACRES was used to simulate rainfall-runoff. The main goal of IHACRES model is to determine the hydrological behavior of the basin using a small number of parameters.
Findings
Based on the results of the temperature assessment in both the near future (2021-2060) and the far future (2061-2100) and under all emission scenarios, it is increasing and the temperature increase in the far future is more than the near future. The lowest and highest temperature increase is respectively related to the RCP 2.6 scenario in the near future period of 0.17°C and the RCP 8.5 scenario in the far future period to the extent of 1.01°C compared to the base period (1981-2005). By examining the trend of changes in the average precipitation in the coming periods, it can be seen that the precipitation, contrary to the temperature, is decreasing in all scenarios, so that the lowest and the highest decrease, respectively, related to the RCP 2.6 scenario in the future period is close to 7.23 mm and The RCP 4.5 scenario will be 25.77 mm in the far future period compared to the base period. Runoff will decrease in future periods under all scenarios. The lowest and highest decrease in the order of the near future (2021-2060) under the RCP 2.6 scenario is 0.08 m3s-1 (8.51%) and the far future (2061-2100) under the RCP 4.5 scenario is 0.08 m3s-1 It is 0.18 (19.15%).
Conclusion
In this study, the effects of climate change on the runoff entering the Nahand dam were investigated using general atmospheric circulation models (GCM) and the fifth report (AR5) of the International Panel on Climate Change (IPCC) with the CanESM2 climate model under RCPs emission scenarios. The results of the climate change study on the entrance to Nahand Dam show that the runoff will decrease under the influence of this phenomenon, so that under the RCP 4.5 scenario, the runoff will decrease by 19.15% in the far future period.