Evaluation of the Effects of Climate Change on Groundwater Recharge Using a Hybrid Method

Abstract

In this study, a new framework was developed for the estimation of groundwater recharge based on a hybrid method. In this regard, the homogeneous recharge zones were determined by the analytical hierarchy process (AHP). The recharge rates in these zones were calculated using the Thornthwaite and Mather’s method. These zones and their recharge rates were entered into the MODFLOW model. Next, the modeling processes, modification of recharge, and calibration of empirical models were interactively continued in the MODFLOW. This way, one of the most important disadvantages of conventional empirical models, i.e., ignoring the physical properties of the aquifer, was resolved by considering the main parameters such as soil properties, unsaturated thickness, land cover, irrigation, and precipitation in the resulting nonlinear equations. The low root mean square error values (less than 5.2) for all equations and high values of the coefficient of determinations indicated the accuracy and reliability of the models. The results of this hybrid method were a series of independent, cost-effective, rapid, and simple to use empirical equations for recharge estimation. As an example for the application of this method, the effects of climate change on groundwater recharge were evaluated in the study area. The obtained results showed that climate change would reduce the recharge rates of the homogeneous zones differently. Moreover, the recharge rate had a general decreasing trend in all regions. Overall, the total annual recharge rate would decrease in the plain. This reduction, especially in the west of the plain which is one of the most important sources of recharge supply, is considerable and will turn the entire plain vulnerable. In general, little reduction in rainfall or increase in temperature would have significant effects on groundwater recharge in the region. Therefore, due to the high dependence of this plain on groundwater resources, special planning is required for the exploitation of groundwater resources in the region.