Effects of Climate Change on Groundwater Recharge (Case Study: Sefid Dasht Plain)

Nowadays, the issue of climate change and its related problems are fundamental crisis in water resource management. On the other hand, considering that groundwater is the most important water resources, determination of the effects of climate change on groundwater and estimation the amount of their recharge will be necessary in the future.
In this research, to analyze the effects of climate change scenarios on groundwater resources, a case study has been applied to the Sefid Dasht Plain located in Chahar Mahal and Bakhtiari Province in Iran. One of the three Atmospheric-Ocean General Circulation Models (AOGCM) which is called HadCM3, under the emission scenarios A2 and B1 is used to predict time series of climate variables of temperature and precipitation in the future. In order to downscale the data for producing the regional climate scenarios, LARS-WG model has been applied. Also, IHACRES model is calibrated and used for simulation of rainfall - runoff with monthly temperature, precipitation and runoff data. The predicted runoff and precipitation production in future have been considered as recharge parameters in the ground water model and the effects of climate change scenarios on the ground water table has been studied. To simulate the aquifer, GMS software has been used. GMS model is calibrated in both steady and unsteady state for one year available data and verification model has been performed by using the calibration parameters for four years.
Results of T- test shows that LARS-WG model was able to simulate precipitation and temperature selected station appropriately. Calibration of IHACRES model indicated the best performance with τw=6 æ f=7.7 and the results shows that IHACRES model simulated minimum amount of runoff appropriately. Although it didn’t simulate the maximum amount of runoff accurately, but its performance and Nash coefficient is acceptable. Results indicate that changes of monthly precipitation in the future period are less than the base period in both scenarios A2 and B1. Precipitation increases about 26 and 33 percent under the scenario B1 and A2 respectively in the future compared to the base period. The monthly average temperature in the future compared to monthly average temperature in the base period has been increasing in both scenarios about 1 degree. Root Mean Square Error criteria for aquifer simulation was 1.6 in steady state and 1.9 in unsteady state. This result indicates that the aquifer has been accurately simulated. Assuming the same rate of pumping wells in the future period and in the base period, despite the increasing of recharge in the future period, water levels decrease notably in the central plains due to exceeding operation. At the end of the period (year 2035) the amount of cumulative groundwater recharges in the scenario A2 compared to scenario B1 increases about 10 cubic meters per second, which shows that the impacts of climate change in the A2 scenario compared to the B1 scenario is more.
Study the impact of climate change is important in our country because the major uses of water supply of groundwater. Enormous use of this resource has been defected aquifer problematically. So, it is necessary to survey impacts of climate change in future period on recharge and water levels aquifer by modeling and simulation. It is useful to predict the future conditions of groundwater. Although the recharge increases in future period, but with respect to high rate of groundwater use, it is impossible to achieve an equivalent level of aquifer without any planning. We need to control on pumping well and treatment of aquifer such as underground water dam, artificial recharge and etc. results of this research can be evaluated by other climatic scenarios, downscaling models and rainfall-runoff models. The results of this research, considerably helps to assess the effects of climate change scenarios on ground water resources as well as its proper planning and management.