| dc.description.abstract | Groundwater is important for supporting ecosystems and assuring human resilience to significant and unpredictable climatic change, especially as surface water systems become more unsustainable due to fast population expansion and climate change. Therefore, groundwater use has become a flexible and adaptive feature for usage demands. However, there are currently fewer studies evaluating the effective management of water resources to be aware of the possible impact of climate change on the combination between the land surface and subsurface in local areas. The objectives of this study were to apply the coupled SWAT-MODFLOW models, which include the Soil Water Assessment Tool (SWAT) and Modular Three-Dimensional Finite-Difference Groundwater Flow (MODFLOW-NWT), to estimate streamflow discharge, groundwater recharge, and water exchange between surface water and groundwater in the Choushui River Alluvial Fan, Taiwan. For further comprehensive strategies, the research assessed the distribution and proportion of recharge areas and the impact of future climate change scenarios influence on groundwater recharge. The finest practical spatiotemporal resolutions of five kilometres over 100 years were selected to accommodate the future climatic conditions of catchment features provided by TCCIP. A strong association exists between simulation and actual observations, as shown by the input′s calibration and verification of the output parameters (streamflow and groundwater level) results. Confidence in the calibrated model was enhanced by validation through generally good statistical performance for the temporal pattern of streamflow and groundwater level, with the Nash–Sutcliffe model efficiency coefficients, R2, percent bias, root mean squared error, and mean absolute error, respectively, which helps achieve a reliable simulation of the watershed response. The results showed that the calibrated and validated SWAT model in the Choushui river were 0.920 and 0.846, respectively, for NSE. For the case of the Pei-Kang river, the NSE values for calibration and validation were 0.549 and 0.548, respectively. Computing the groundwater head of the high correlation (NSE = 0.98) and small error (3 m) revealed that the groundwater recharge from the SWAT model utilized is consistent with the hydrogeological model in the study area and provided the background for coupled SWAT-MODFLOW. The spatiotemporal variability of groundwater recharge for 2005-2100 was estimated under the baseline and four representative concentration pathways (RCPs) scenarios. The findings showed that recharge mainly occurs in the proximal fan area, catching up with some high potential recharge locations with previously delineated sensitive areas for groundwater recharge in literature. The results also showed that during the dry years, the recharge rate from the streams to the shallow aquifer was lower than the groundwater portion discharge to the streams. Besides, the climate change signal predominates the annual variability, resulting in a more pronounced pattern of greater recharge concentrated in a few years. This study expressed the procedure for assessing the impact of climate change on groundwater recharge based on the top one ranking (MIROC5) projection of the GCMs. The maximum and minimum impact rates of climate change on groundwater recharge in the study area from the 2020s to the 2100s were RCP2.6 (66.36%, -41.92%), RCP4.5 (51.86%, -39.48%), RCP6.0 (56.11%, -40.13%), or extreme climate RCP8.5 (48.93%, -39.85%), respectively. The result suggests that even when groundwater recharge lies in geology and soil properties, the effects of climate change still substantially influence it. The well-tested coupled model would be a valuable tool for evaluating a wide variety of realistic scenarios in order to determine the most efficient and workable water resource management plans for replenishing the critically depleted surface water and groundwater supplies. These findings help decision-makers and stakeholders devise sustainable water resource strategies. | en_US |