Simulation of the impacts of climate and land-use change on groundwater level in the Hashtgerd plain, Iran

Groundwater is one of the most important sources of water supply in arid and semi-arid regions, but its availability with sustainable quantity and quality is threatened by various factors, among which climate and land-use change have the most important role. Therefore, it is essential to achieve reliable methods for predicting changes in aquifer storage to plan for the sustainable use of groundwater resources. This study aimed to estimate the potential impact of climate change and land use on the groundwater level of Hashtgerd plain for sustainable use of groundwater resources. In this regard, groundwater supply and demand for 2020 as the base year was simulated to forecast the trends until 2050 by considering climate and land-use changes. Five General Circulation Models under four Representative Concentration Pathways (RCP2.6, RCP4.5, RCP6, and RCP8.5) were used to project future rainfall and temperature. The LARS-WG model was used to downscale the climatic data. Classification of land-use was performed using Landsat satellite images of 1990, 2005, and 2020 in ENVI 5.3 software. Then, by these maps, the Markov chain method implemented in TerrSet software was used to model land-use change for 2050. The indexes used to evaluate the model were the overall accuracy of prediction and the kappa coefficient. The overall accuracy of 94.34% and kappa coefficient of 0.92 were in the calibration stage and 86.34 and 0.82 in the validation stage, respectively. Finally, the effect of climate and land-use change on the decrease of groundwater level was simulated using the MODFLOW model for the period 2020–2050. RMSE and MAE values of steady-state calibration were 0.91 and 0.75, respectively. These values were estimated to be 0.97 and 0.8 in the calibration step for the unsteady-state and 1.01 and 0.91, respectively, in the validation step. The results of climate change showed a decrease in the average annual precipitation and an increase in the average annual temperature. The annual temperature increased by 1.4 °C and 3.2 °C for RCP 4.5 and 8.5 respectively, by 2050. The annual precipitation decreased by 2.45% and 4.47% for both scenarios. The results of land-use change show an increase of residential, barren, and agricultural lands by 105, 41, and 8%, respectively, and a decrease of 94% in pastures lands. The future land-use change reduced aquifer reserve by up to 41%. The combined impacts of climate and land-use change in the most critical state reduced aquifer reserve by 61%.