Investigation the effect of climate change scenarios on the monthly flow discharge at the outlet of Gelevard Dam

In recent years, hydrological models such as the SWAT model have been widely used by managers and hydrologists as a tool to identify natural and human activities affecting the basin hydrological system and their management and planning. As the eastern plains of Mazandaran is the only forbidden groundwater harvesting area in the north of the country, thus, with accurate prediction of inflow to the Gelevard dam for future periods, can provide accurate planning for downstream water supplies and manage demand for water and agricultural development. Therefore, the purpose of this study was to investigate the effect of climate change on the fluctuations of the flow discharge of Gelevard Dam in the east of Mazandaran province.

In this study, HadGEM2 and EC-Earth models were used to produce the minimum and maximum temperature and precipitation data for the period of 2021-4040 using a combination of Berma station data and global data at the Gelevard Dam. The LARS-WG6 model was used to fine-tune this data. Also, the Mann-Kendall and Sen Gradient tests were used to study the trend of climate parameters. Then, the data were entered to the SWAT model which was calibrated using local data and information (from 1984 to 2010 for calibration and 2011 to 2014 for validation) and the runoff changes were evaluated. The accuracy of the SWAT model in simulation of the output current was evaluated using evaluation indexes.

The results showed that the climate change had negative effects on the climate of the Gelevard dam area which increased the minimum and maximum temperatures by 1.40 and 2.40 °C, respectively. The SWAT model appropriately simulated the time of peak discharge and the peak discharge values so that it corresponds to the time of high rainfall event. Comparison of the effects of precipitation and the minimum and maximum temperatures on the outflow indicates that the effects of temperature are more than the precipitation, so that in the basic period, the minimum temperature is equal to 1.41 and the maximum temperature is 2.34. Also, the changes of monthly mean discharges in RCP4.5 (-0.01) and RCP8.5 (-0.11) scenarios are lower than the observed discharges (-0.16) and the output discharge is reduced in the hot months of the year. With investigation of the percentage of difference between maximum and minimum temperature and rainfall under RCP4.5 and RCP8.5 scenarios compared to the base period found that increasing of temperature caused more reduction in outflow rate in the future period. So that the effect of climate change on rainfall-runoff process reduced the water resources of Gelevard dam by 13%. The results of sensitivity analysis showed that soil evaporation coefficient, average length (slope), mean air temperature for snowfall (degree Celsius) and curve number in moisture conditions had the most effect on the output discharge.

The results, irrespective of the changes in each component, indicate the importance of the temporal pattern of changes throughout the year which has an important role in the water resources management of the basin. The results of the present study, emphasize the importance of potential effects of climate change at basin hydrology status, highlights the climate change and implications in the management of water resources in the Gelevard Dam.