Assessment of Climate Change Impact on Groundwater Quantitative Status in the Dehgolan Aquifer Using the MODFLOW Model

Extended Abstract Background: Monitoring and evaluating water resources are crucial steps in increasing the knowledge of a country's water resource conditions. The results of these investigations should inform water resource management. Iran, with its arid and semi-arid climate, faces challenges due to low rainfall rates and uneven distribution. Climate change has further complicated these issues, affecting meteorological variables and the hydrological cycle. Factors such as population growth, urbanization, industrialization, and agricultural development have increased water demand. The increased use of groundwater in arid regions has led to a decrease in groundwater storage. To address the negative balance of Dehgolan groundwater resources and prevent depletion, the Regional Water Company of Kurdistan announced the development of Dehgolan groundwater resources in 2003. This research aims to investigate the quantitative effects of climate change on the Dehgolan aquifer, the largest aquifer in Kurdistan Province. Utilizing climate models to predict climate change and integrating them with hydrological models can help predict future hydrological changes. Methods: The Dehgolan plain, the largest plain in Kurdistan Province, covers an area of 982.8 km2. This plain is located between the longitudes 47˚10' to 47˚45' and the latitudes 35˚05' to 35˚35'. The Dehgolan aquifer and Talvar catchment areas are 779.8 km2 and 2491 km2, respectively. The geophysical studies determined the Dehgolan aquifer as an unconfined aquifer. The elevation in the Dehgolan aquifer ranges from 1740 to 2045 m. Various land uses cover the watershed, with dryland farming, range, irrigated agriculture, residential areas, and water bodies accounting for different percentages. Climate data, including rainfall and temperature, were collected. The average annual rainfall in the Dehgolan Plain is 319.32 mm. The average annual temperature ranges between 9.39 and 9.12 ˚C, respectively. This study utilized the IPCC Fifth Assessment Report to predict meteorological variables (minimum and maximum temperature, precipitation, and relative humidity) under different scenarios including RCP2.6, RCP4.5, and RCP8.5 using the SDSM model. The MODFLOW model was employed for 3D groundwater flow modeling. The conceptual model of the Dehgolan aquifer was developed in GMS software, incorporating boundary conditions, aquifer network, and other parameters. Monthly elevation of the water table was estimated under RCP2.6, RCP4.5, and RCP8.5 scenarios. Simulation and prediction were conducted for specific periods. Groundwater information from September 2008 to September 2017 was used for model calibration, and then groundwater was predicated for 10 hydrological years from September 2017 to September 2027. Model efficiency was evaluated using various coefficients such as R2, ENS, PBIAS, and MAE. Results: The SDSM and MODFLOW models showed accuracy in simulating climate variables and groundwater flow. Maximum similarity between simulated and observed data belonged to minimum and maximum temperatures. Sensitivity analysis revealed hydraulic conductivity as the most sensitive parameter whereas the specific yield had the least effect on groundwater changes. Results from the MODFLOW model projected a negative balance in the Dehgolan aquifer under different scenarios. Under the RCP2.6, RCP4.5, and RCP8.5 scenarios, the average annual water table in the predicted period will be -1.60, -1.61, and -1.36 m, and the average annual groundwater storage will be -23.69, -23.85, and -20.21 mcm, respectively. The RCP2.6 and RCP4.5 scenarios indicated a more critical situation than RCP8.5. Conclusion: Climate models and RCP scenarios suggest changes in climatic conditions and hydrological processes in the Talvar River basin. Increased atmospheric temperatures and decreased precipitation will impact groundwater resources. The high atmospheric temperature will increase the rate of evaporation. High evaporation should have negative impacts on both quantitative and qualitative parameters of groundwater resources. The future may see fluctuations in groundwater levels following natural patterns.