Yoloğlu et al. (2026) Groundwater sustainability for irrigation in the semi-arid Konya Closed Basin, Türkiye, under climate change scenarios

Identification

• Journal: Hydrogeology Journal
• Year: 2026
• Date: 2026-03-30
• Authors: Onur Cem Yoloğlu, İrem Daloğlu Çetinkaya, Nadım K. Copty
• DOI: 10.1007/s10040-026-03052-z

Research Groups

• Institute of Environmental Sciences, Boğaziçi University, Istanbul, Türkiye

Short Summary

This study assesses groundwater sustainability in the semi-arid Konya Closed Basin, Türkiye, under climate change and agricultural scenarios using a coupled groundwater flow model and the net inflow concept. It concludes that combining enhanced irrigation efficiency with a shift to traditional rainfed crops is crucial for mitigating groundwater overexploitation and achieving sustainable use.

Objective

• To assess the impact of climate change scenarios and agricultural practices on groundwater sustainability in the semi-arid Konya Closed Basin, Türkiye, using a coupled unsaturated-saturated groundwater flow model and the net inflow concept.

Study Configuration

• Spatial Scale: The entire Konya Closed Basin (KCB), an endorheic agricultural basin in central Türkiye, covering an area of 50,000 square kilometers. The flow domain was discretized into uniform 10 km × 10 km cells.
• Temporal Scale: The model was calibrated for the period from January 2000 to December 2022. Scenario analyses and future projections were conducted for the period from 2023 to 2040.

Methodology and Data

• Models used:
  • MODFLOW (Modular Three-Dimensional Finite-Difference Ground-Water Flow Model)
  • UZF (Unsaturated-Zone Flow) package, coupled with MODFLOW, to simulate transient vertical water flow through the vadose zone.
  • Net inflow concept for post-processing and scenario evaluation.
  • 17 high-resolution regional climate model (RCM) and global circulation model (GCM) projections from the EURO-CORDEX framework (EUR-11, approximately 12.5 km resolution) for climate change scenarios (RCP4.5 and RCP8.5).
• Data sources:
  • Groundwater level observations from 29 long-term monitoring wells (January 2000 – December 2022).
  • Annual crop cultivation areas at the district level from the Turkish Statistical Institute (TUIK 2023).
  • Monthly crop water requirements for the Konya region from Türkiye's General Directorate of Agricultural Research and Policies (TAGEM 2017).
  • Monthly precipitation data spatially interpolated from 18 meteorological stations.
  • Aquifer properties (hydraulic conductivity, specific yield) derived from 81 pumping tests and geological maps.
  • Soil characterization studies for unsaturated zone parameters (residual saturation, pore-size distribution index).
  • Stakeholder input (farmers, NGOs, water authorities) for developing water management scenarios.

Main Results

• Historical Trends (2000-2022): Groundwater levels in the basin experienced a severe average drop of approximately 0.9 meters per year between 2000 and 2010 due to low irrigation efficiency. While government incentives led to a temporary slowdown in decline (2010-2015), a shift to more water-demanding crops (e.g., corn) and expansion of irrigated land caused a continued average drop of about 0.7 meters per year over the entire simulation period.
• Business-as-usual Scenario (2023-2040): Under both RCP4.5 and RCP8.5, groundwater levels are projected to continue declining, with an average annual drop ranging between 0.1 and 0.5 meters (median of 0.28 meters). This indicates that current practices are unsustainable, and benefits from past irrigation efficiency improvements are eroding.
• Enhanced Irrigation Efficiency Scenario (2023-2040): Increasing irrigation efficiency linearly from 0.65 to 0.80 by 2028 results in a median annual drawdown close to zero (average of 0.06 meters). However, drawdown is observed to increase in later years (2035-2040), suggesting that this measure alone would be short-lived in achieving sustainability.
• Combined Scenario (Enhanced Irrigation Efficiency + Corn Phase-out): This scenario, which combines increased irrigation efficiency (to 0.80) with a reduction of corn cultivation to 2005 levels (replaced by wheat), shows the most promising results. The median annual drawdown is projected to be near zero, ranging between +0.18 meters and -0.18 meters, indicating that this combined strategy can lead to sustainable groundwater use.
• Climate Projection Uncertainty: The analysis highlights substantial uncertainty in future groundwater level changes due to variations among the 17 GCM-RCM climate projections, emphasizing the need for flexible water management policies.

Contributions

• Developed a novel approach combining a coupled unsaturated-saturated groundwater flow model (MODFLOW/UZF) with the net inflow concept to assess groundwater sustainability under climate change and agricultural practices in a data-scarce, heavily exploited semi-arid basin.
• Indirectly estimated unmetered groundwater abstraction rates using cultivated crop areas, crop water requirements, and calibrated irrigation efficiency, providing a practical solution for regions with limited direct pumping data.
• Demonstrated that technological improvements in irrigation efficiency alone are insufficient for long-term groundwater sustainability in the study area; a combined strategy involving both enhanced irrigation efficiency and a shift back to traditional, less water-intensive crops (e.g., wheat instead of corn) is essential.
• Provided a robust, evidence-based management tool and methodology that can be extended to other water-stressed agricultural regions globally facing similar challenges of groundwater overexploitation and climate change.
• Utilized the net inflow concept as an easily understandable tool for communicating complex hydrological modeling results to stakeholders, facilitating informed water management decisions.

Funding

• Scientific and Technological Research Council of Türkiye (TÜBİTAK)
• InTheMED project, part of the PRIMA programme, supported by the European Union's HORIZON 2020 research and innovation programme under grant agreement No 1923.

Citation

@article{Yoloğlu2026Groundwater,
  author = {Yoloğlu, Onur Cem and Çetinkaya, İrem Daloğlu and Copty, Nadım K.},
  title = {Groundwater sustainability for irrigation in the semi-arid Konya Closed Basin, Türkiye, under climate change scenarios},
  journal = {Hydrogeology Journal},
  year = {2026},
  doi = {10.1007/s10040-026-03052-z},
  url = {https://doi.org/10.1007/s10040-026-03052-z}
}