Reinecke et al. (2026) The ISIMIP groundwater sector: a framework for ensemble modeling of global change impacts on groundwater

Identification

• Journal: Geoscientific model development
• Year: 2026
• Date: 2026-01-15
• Authors: Robert Reinecke, Tanjila Akhter, Annemarie Bäthge, Rachel Dietrich, Sebastian Gnann, Simon N. Gosling, Danielle Grogan, Andreas Hartmann, Stefan Kollet, Rohini Kumar, R. B. Lammers, Sida Liu, Yan Liu, Nils Moosdorf, Bibi S. Naz, Sara Nazari, Chibuike Orazulike, Yadu Pokhrel, Jacob Schewe, Mikhail Smilovic, Maryna Strokal, Wim Thiery, Yoshihide Wada, Shan Zuidema, Inge de Graaf
• DOI: 10.5194/gmd-19-523-2026

Research Groups

• Institute of Geography, Johannes Gutenberg-University, Mainz, Germany
• Department of Civil and Environmental Engineering, Michigan State University, East Lansing, Michigan, USA
• Chair of Hydrology, University of Freiburg, Freiburg, Germany
• School of Geography, University of Nottingham, Nottingham, United Kingdom
• Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA
• Institute of Groundwater Management, TU Dresden, Dresden, Germany
• Agrosphere (IBG-3), Institute for Bio- and Geosciences, Research Centre Juelich, Juelich, Germany
• Department Computational Hydrosystems, Helmholtz Centre for Environmental Research GmbH – UFZ, Leipzig, Germany
• Earth Systems and Global Change Group, Wageningen University and Research, Wageningen, the Netherlands
• Leibniz Centre for Tropical Marine Research (ZMT), Bremen, Germany
• Institute of Geosciences, Kiel University, Kiel, Germany
• Potsdam Institute for Climate Impact Research, Member of the Leibniz Association, Potsdam, Germany
• Water Security Research Group, International Institute for Applied Systems Analysis, Laxenburg, Austria
• Chair of Hydrology and Water Resources, ETH Zurich, Zurich, Switzerland
• Vrije Universiteit Brussel, Department of Water and Climate, Brussels, Belgium
• Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia

Short Summary

This paper introduces the new ISIMIP Groundwater sector, a framework for multi-model ensemble simulations of global change impacts on groundwater. It outlines the sector's protocol and demonstrates significant inter-model differences in simulated water table depth and groundwater recharge, highlighting the need for ensemble assessments.

Objective

• To establish the new ISIMIP Groundwater sector, integrating multiple global, continental, and regional-scale groundwater models for ensemble impact assessments of global change.
• To provide a comprehensive understanding of groundwater representation in large-scale models, identify uncertainties, and enhance the robustness of predictions regarding global change impacts on groundwater and connected systems.

Study Configuration

• Spatial Scale: Global, continental, and regional scales, with a targeted output resolution of 5 arcminutes (approximately 9.25 kilometers at the equator). Individual models operate at resolutions ranging from 30 arcseconds (approximately 0.9 kilometers) to 0.5 degrees (approximately 55.5 kilometers).
• Temporal Scale: Historical period from 1901 to 2019 (ISIMIP3a) and future projections (ISIMIP3b). Model simulations typically use daily timesteps, with outputs aggregated to monthly resolution for intercomparison.

Methodology and Data

• Models used: Water Balance Model (WBM), Community Land Model (CLM), Community Water Model (CWatM), Global Gradient-based Groundwater Model (G3M), VIC-WUR-MODFLOW (VIC-wur), V2KARST, Global Groundwater Rain-fed Recharge (GGR), ParFlow.
• Data sources: Bias-adjusted climate models from CMIP6 ensemble (ISIMIP framework), observational climate data (obsclim), historical socioeconomic data (histsoc). Specific model forcings include WaterGAP 2.2d, MSWEP V2, GLDAS, ERA5, GRanD v1.1, LUH2, FAO AQUASTAT, GFDL-ESM4, GSWPv3, chelsa-W5E5v1.0, and GSWP3-W5E5.

Main Results

• Eight diverse groundwater models are integrated into the ISIMIP Groundwater sector, providing between 1 and 19 of the 23 defined output variables.
• Significant inter-model differences exist in simulated global arithmetic mean water table depth, ranging from 6 meters to 127 meters at simulation start.
• Global arithmetic mean groundwater recharge also varies substantially among models, from 78 millimeters per year to 228 millimeters per year (or 332 millimeters per year including V2KARST), with distinct spatial patterns of disagreement.
• Preliminary analysis of relative changes in groundwater recharge between 2001 and 2006 shows plausible regional changes, such as decreases in Spain and Portugal consistent with drought conditions, and increases in arid regions like the Sahara, Middle East, Australia, and Mexico.

Contributions

• Establishes the first long-term, community-driven, structured model intercomparison project for groundwater models at regional to global scales.
• Provides a framework for compiling a multi-model ensemble to systematically assess the impacts of global change on groundwater and quantify associated model and scenario uncertainties.
• Enhances cross-sectoral activities within ISIMIP, fostering interlinkages with other sectors (e.g., Global Water, Water Quality) to enable interdisciplinary assessments of climate change impacts.
• Serves as a foundation for developing better modeling frameworks, critically examining current modeling practices, and creating new datasets for model parameterization and assessment.
• Aims to provide scientific evidence for policy-relevant reports, such as the European Climate Risk Assessment (EUCRA) and the IPCC Assessment Reports, addressing a critical gap in global change impact assessments.

Funding

• Johannes Gutenberg University Mainz (for open-access publication).
• The ISIMIP Groundwater sector itself is a community-driven effort without specific external funding.

Citation

@article{Reinecke2026ISIMIP,
  author = {Reinecke, Robert and Akhter, Tanjila and Bäthge, Annemarie and Dietrich, Rachel and Gnann, Sebastian and Gosling, Simon N. and Grogan, Danielle and Hartmann, Andreas and Kollet, Stefan and Kumar, Rohini and Lammers, R. B. and Liu, Sida and Liu, Yan and Moosdorf, Nils and Naz, Bibi S. and Nazari, Sara and Orazulike, Chibuike and Pokhrel, Yadu and Schewe, Jacob and Smilovic, Mikhail and Strokal, Maryna and Thiery, Wim and Wada, Yoshihide and Zuidema, Shan and Graaf, Inge de},
  title = {The ISIMIP groundwater sector: a framework for ensemble modeling of global change impacts on groundwater},
  journal = {Geoscientific model development},
  year = {2026},
  doi = {10.5194/gmd-19-523-2026},
  url = {https://doi.org/10.5194/gmd-19-523-2026}
}