Höckh et al. (2026) Screening the Future Security of Groundwater-based Water Supply on the Scale of a Regional Water Supplier

Identification

• Journal: Water Resources Management
• Year: 2026
• Date: 2026-02-16
• Authors: Frederick Höckh, Michael Finkel, Andreas Morhard, Olaf A. Cirpka
• DOI: 10.1007/s11269-025-04481-3

Research Groups

• Department of Geosciences, University of Tübingen, Germany
• GIT HydroS Consult GmbH, Freiburg, Germany

Short Summary

This study develops a simple, low-cost screening framework using a novel Groundwater Use Index (GWUI) to assess the future security of groundwater-based water supply under climate change. Applied to a regional water supplier in southwest Germany, the framework projects significant water stress and potential shortages by 2070, even in a historically humid region, primarily due to declining groundwater recharge.

Objective

• To propose a novel, easily implementable screening framework, based on a new Groundwater Use Index (GWUI), to assess the future security of groundwater-based water supply by considering changes in water availability and demand on different time scales and at monthly resolution.

Study Configuration

• Spatial Scale: Two regional groundwater catchments (Oberes Gäu and Neckar valley) of the Ammertal-Schönbuch Gruppe (ASG) water supplier in Baden-Württemberg, southwest Germany, covering approximately 113 square kilometers of recharge area.
• Temporal Scale: Historical analysis from 2000 to 2022 (with recharge trends from 1990-2023); future projections up to 2070. Monthly resolution for water demand and availability, with GWUI evaluated over averaging periods of 35, 36, 60, and 120 months.

Methodology and Data

• Models used:
  • Soil-water-budget model: GWN-BW (Gudera and Morhard 2015) for groundwater recharge estimation.
  • Climate models: Ensemble of 13 CMIP5 generation Global Climate Models (GCMs) (EC-EARTH, MIROC5, HadGEM2, MPI-ESM, CanESM2) from the KLIWA project, downscaled using dynamic and statistical methods (e.g., WETTREG2018, CCLM4-8-17, Episodes2018) for RCP8.5 emission scenario.
  • Empirical Climate Scenario (ECS): Combines historical hydrological winter and summer half-years to match projected temperature trends.
• Data sources:
  • Historical meteorological data (precipitation, air temperature, relative humidity, sunshine duration/global radiation, wind speed) from the German Weather Service (DWD).
  • Historical public water demand data from the Ammertal-Schönbuch Gruppe (ASG) water supplier.
  • Hydrogeological data: Geological maps, soil maps, land-use maps (CORINE Land Cover dataset), digital elevation models (LGL 2025), hydrogeological maps, water protection zones, and tracer test data.
  • Future population projections from the German Federal Office of Statistics (Bundesamt für Statistik 2022).

Main Results

• Historical groundwater recharge in the study area showed a significant decline, from an average of 152 millimeters per year (1990-2000) to 92 millimeters per year (2020-2023), representing an almost 40% reduction.
• The newly introduced Groundwater Use Index (GWUI) with an optimized averaging period of 35 months (GWUI35) effectively correlated with historical water stress events experienced by the supplier. Historically, GWUI35 values exceeding 35% over multiple consecutive months indicated a considerable risk of water levels falling below operational thresholds.
• Future projections by 2070 indicate widespread water insecurity: GWUI120 values are projected to exceed 40% in most scenarios, and GWUI35 values over 40% are expected within the next decade in all scenarios, intensifying to partly exceed 60% after 2050.
• The most pessimistic climate model combination (HadGEM2+WETTREG2018), which best reproduced the observed historical decline in groundwater recharge, projects recurring critical situations for the water supplier, with GWUI values consistently exceeding 40%.
• Even scenarios based on the Empirical Climate Scenario (ECS), which assume nearly stagnant recharge rates, show a shift in GWUI distribution of up to 10% compared to historical values, primarily due to projected changes in water demand.
• The study concludes that the current infrastructure and operating conditions will likely be insufficient to meet water demand during periods of low groundwater availability under pessimistic future scenarios.

Contributions

• Proposes a novel, simple, and low-cost screening framework for assessing the future security of groundwater-based water supply, addressing the need for practical tools for regional water suppliers.
• Introduces the Groundwater Use Index (GWUI) as a versatile indicator that can be calibrated to local conditions and historical stress events (e.g., optimal N=35 months for the study area).
• Demonstrates the framework's ability to consider changes in water availability and demand on different time scales (monthly resolution, decadal and sub-decadal GWUI), capturing seasonal and inter-annual fluctuations.
• Provides a critical assessment for a region in southwest Germany, highlighting that even areas traditionally considered resilient to climate change (humid climate, no irrigation, long-distance water supply) face significant future water stress.
• Emphasizes the importance of selecting climate projections that align with recent historical trends, even if they represent more pessimistic outcomes than ensemble means, for robust water supply planning.

Funding

• German Federal Ministry of Research, Technology, and Space (BMFTR) (project number: 02WGW1670).

Citation

@article{Höckh2026Screening,
  author = {Höckh, Frederick and Finkel, Michael and Morhard, Andreas and Cirpka, Olaf A.},
  title = {Screening the Future Security of Groundwater-based Water Supply on the Scale of a Regional Water Supplier},
  journal = {Water Resources Management},
  year = {2026},
  doi = {10.1007/s11269-025-04481-3},
  url = {https://doi.org/10.1007/s11269-025-04481-3}
}