Studying Groundwater Resources Balancing Plan under Climate Change Conditions (Case Study: Hashtgerd Study Area)

The purpose of this study is to evaluate the balancing strategies of groundwater resources in order to adapt to climate change. Accordingly, the simulation of two parameters of precipitation and temperature in Hashtgerd region with three climatic models HadGem2Es, EC-ERATH and GFDL-CM3, was performed using three emission scenarios RCP2.6, RCP4.5 and RCP8.5. Groundwater resources are one of the most important sources of water supply in arid areas, especially in areas facing surface water shortages. This shortage, along with climate stress, has made the water resource utilization system complex. The complexities of water resources systems along with unplanned exploitation of groundwater resources and the strong dependence of operators on it have made the development of a systemic approach in water supply and demand management for development clear. Due to the decline in groundwater aquifers, management of abstraction from these resources and control of abstraction is very important and many aquifer equilibrium scenarios have been proposed to achieve this goal.

Hashtgerd study area with code 4105 is in the division of National Water Resources Management Company-Ministry of Energy located in the west of Alborz province with an area of 1170.6 square kilometers, and with alluvial aquifer with an area of 410.7 square kilometers (Figure 2). This study area is located in the northern half of the Namak Lakebasin. Kordan river, the most important surface water source of this region, originates from the northern part and after passing through the central areas of the plain, it leaves the southern part. Most of the water resources in this area are exploited by wellsAfter climatic simulation, exponential down scaling was performed using LARS-WG v6 model. After evaluating the effect of climate change in the region, in order to evaluate the quantitative status of the aquifer, simulations were performed using the MODFLOW model and the prediction of the future situation under climate change conditions was analyzed.

The results of climatic simulation showed that the simulated values in comparison with the observational data indicate an increase in average precipitation and a decrease in temperature in most months of the year. The difference between the values obtained at the statistical level of 95% indicates a significant difference and appropriateness of simulation results. On the other hand, the quantitative results of the quantification of the aquifer indicate the continuation of the aquifer decline trend and the extracted results show that the highest rate of decline is recorded in the RCP 8.5 release scenario and the lowest rate is recorded in the RCP 2.6 scenario. The rate of aquifer drop in RCP 2.6 scenario was obtained in three models between 7.8 to 8 meters, in RCP 4.5 scenario between 7.9 to 8.8 meters and in RCP 8.5 scenario between 8.5 to 9.7 meters. After evaluating the future situation, aquifer equilibrium scenarios were analyzed in order to adapt to climate change in the region using 5 evaluation strategies by evaluating the relative improvement of the aquifer. The results of balancing strategies showed that in the scenario of drinking water supply through Taleghan dam and replacement of water from wells in the region, it was determined that 20 million cubic meters of water should be allocated for Hashtgerd drinking water supply and replace 20 million cubic meters of water extracted from wells. It becomes. Accordingly, in this scenario, while transferring water and considering the return water coefficient of drinking consumption of 60%, it was determined that a volume equivalent to 32 million cubic meters of water is taken less than the aquifer. The results obtained from the application of various balancing strategies in Hashtgerd aquifer indicate that the aquifer decline continues during the forecast period until the end of the 2024-2025 water year. Examination of the simulation scenarios shows that S1 solution, which is a 15% reduction in water abstraction from the aquifer, has shown the highest efficiency in all three scenarios of climate diffusion in the aquifer. 5. and RCP2.6 will occur at 4 and 3.2 m, respectively. The results also showed that the highest degree of uncertainty in the results of the aquifer level is related to S1 solution and shows a difference of 1.15 meters in the results of diffusion scenarios. The results of this study indicate the importance and necessity of developing strategies for balancing groundwater resources in all study areas of the country, which will be more acute in the event of climate change.