Estimation of Aquifer Recharge of the Semi-Arid Konya Closed Basin in Türkiye under Climate Change

Irrigated agriculture in semi-arid closed basins depends heavily on groundwater, yet the feedbacks between irrigation practice and aquifer recharge remain poorly quantified. The Konya Closed Basin, one of Türkiye's most productive agricultural regions, exemplifies this challenge: with intensive largely unregulated irrigation withdrawals exceeding aquifer recharge leading to rapid declines of groundwater levels. This study develops a coupled unsaturated-saturated flow model based on the MODFLOW/UZF framework to estimate spatiotemporal recharge dynamics across the basin and to assess the sensitivity of recharge and the overall water budget to changes in irrigation efficiency, cropping patterns, and future climate. The model explicitly captures the complex non-linear processes governing water infiltration through the vadose zone and evapotranspiration, with groundwater extraction estimated from historical cultivated areas and crop water demands. Future hydroclimatic conditions were projected using seventeen regional climate models within the EURO-CORDEX framework. Projected climate change through 2040 is modest, so irrigation management and cropping decisions emerge as the dominant controls on recharge dynamics. Moreover, recharge is spatially variable, governed principally by the spatial distribution of precipitation, crop type, and vadose zone hydraulic properties. The highest recharge rates are concentrated in the Beyşehir Lake catchment and along the Taurus Mountain forming the southern basin boundary. Temporally, recharge exhibits somewhat steady rates relative to surface water application, a pattern attributed to the buffering capacity of the thick unsaturated zone, which dissipates and delays peak infiltration signals. Scenario analyses demonstrate that improvements in irrigation efficiency and transitions away from water-intensive summer crops such as corn, while effective in reducing consumptive water use, exert limited influence on irrigation return flow recharge, owing to the dominance of evapotranspiration losses during the summer irrigation period. Recharge rates are estimated at approximately 20–40% of total water application, placing the basin at the upper end of values reported for irrigation-intensive semi-arid regions. These findings underscore the importance of accurate recharge quantification as a prerequisite for sustainable groundwater resource governance in water-scarce, agriculturally dependent semi-arid basins.