A proposed modelling towards the potential impacts of climate change on a semi-arid, small-scaled aquifer: a case study of Iran.

Several studies have evaluated the impact of climate change on the alluvial aquifers; however, no research has been carried out on a small-scale aquifer without any human influences and pumping wells. The object of this study is to assess the response of such an aquifer to the climate change to observe if it can preserve its storage or not. Pali aquifer, southwest Iran, is solely discharged by Taraz-Harkesh stream and geological formations. On the other hand, it is recharged by precipitation and geological formations. The Taraz-Harkesh stream's discharge rates and the Pali aquifer's groundwater level were simulated by IHACRES and MODFLOW, respectively, in the base (1961-1990) and future (2021-2050) time periods under two Representative Concentration Pathways, i.e., RCP4.5 and RCP8.5. The outputs of IHACRES were regarded as the input of MODFLOW. The groundwater model was calibrated in the steady-state for the hydrological year 2007 and in the unsteady-state for the time period 2008-2014 with annual time steps. Further, the groundwater model was verified for the time period 2015-2018. The statistical criteria maintained the groundwater model's ability, consequently measuring the root mean square error to be 0.69, 0.85, and 1.18 m for the steady calibration, unsteady calibration and verification of the groundwater model, respectively. Results indicate that the stream's discharge rates would decrease in the future time period, especially under RCP8.5. Nevertheless, the groundwater level would not fluctuate considerably. Indeed, the groundwater resources, even a semi-arid, small-scaled aquifer, may be considered as the water supplying systems under the future climate change.