The effect of climate change on surface and groundwater resources using WEAP-MODFLOW models

In addressing management scenarios and climate changes, it is necessary to consider surface water and groundwater resources as an integrated system. In this context, the present research first simulates and evaluates surface water and groundwater simultaneously; then, it examines the possible effects of climate change on these water resources in the study area (Mahabad, Northwest of Iran). In the first stage, the WEAP-MODFLOW model was applied to a 10-year period (2006-2015) in order to take into account the interactions between surface water and groundwater and calibrate the amount of recharge and drainage from the aquifer. In the second stage, in order to study the effect of climate change on surface water and groundwater resources, we compared the micro-scale model outputs under the RCP4.5 scenario for different climate change models in the period 2021-2045. The results show that root-mean-square error (RMSE) and mean absolute error (MAE) scores are equal to 0.89 and 0.79 in unsteady conditions, respectively, which confirm the efficient performance of groundwater simulation. In addition, the results of the WEAP model based on MARE assessment criteria for calibration and validation modes are equal to 0.54 and 54.0, respectively. This finding provides evidence for the efficient performance of the simulation model. Once the interactions between groundwater and surface water were specified, the results R-2 and NS suggested that indices were equal to 0.62 and 0.59, respectively, for Mahabad hydrometric station. The efficient performance of the proposed model for runoff simulation was therefore confirmed. Owing to climate change in the study period, groundwater decreased by about 1.6-1.9 m. Moreover, the amount of runoff declined from 0.1 to 0.001 MCM/month in all months except December. Unless appropriate decisions are taken to improve groundwater and strategies are applied to reduce the effect of climate change, under the present conditions this region will suffer irreparable damages in the future.