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| Hydrological Ensemble Prediction Experiment | |
|---|---|
| Name | Hydrological Ensemble Prediction Experiment |
| Abbreviation | HEPEX |
| Formation | 2004 |
| Purpose | Improve hydrological ensemble forecasting and prediction |
| Headquarters | Global |
| Region served | Worldwide |
Hydrological Ensemble Prediction Experiment is an international initiative focused on advancing ensemble forecasting for rivers, watersheds, reservoirs, and flood risk through coordinated research, operational trials, and community building. It unites researchers, operational agencies, and international bodies to link atmospheric, hydrological, and decision-support modelling while promoting standards, verification, and open collaboration. The initiative interfaces with global projects, national services, and regional consortia to translate ensemble science into operational practice.
HEPEX brings together experts from European Centre for Medium-Range Weather Forecasts, National Oceanic and Atmospheric Administration, World Meteorological Organization, World Bank, United Nations Educational, Scientific and Cultural Organization, International Hydrological Programme, Food and Agriculture Organization of the United Nations, United Nations Office for Disaster Risk Reduction, International Commission for the Protection of the Rhine, Global Runoff Data Centre, European Flood Awareness System, Global Water Partnership, International Association of Hydrological Sciences, United Nations Environment Programme, Intergovernmental Panel on Climate Change, European Space Agency, National Aeronautics and Space Administration, Japan Meteorological Agency, Met Office (United Kingdom), Deutscher Wetterdienst, Météo-France and national hydrological services to foster ensemble prediction capabilities. The experiment emphasizes coupling between atmospheric ensembles such as from ENS and hydrological models used by United States Geological Survey, Australian Bureau of Meteorology, Hydrologic Engineering Center, Swiss Federal Office for the Environment, Finnish Meteorological Institute and research groups at Massachusetts Institute of Technology, ETH Zurich, University of Oxford and Imperial College London.
HEPEX was initiated in the early 2000s with formative meetings that included participants from European Centre for Medium-Range Weather Forecasts, World Meteorological Organization, National Oceanic and Atmospheric Administration and academic institutions such as University of California, Berkeley, Colorado State University, Delft University of Technology, University of Melbourne, Peking University and Tsinghua University. Milestones include coordinated workshops at venues linked to International Association of Hydrological Sciences assemblies and symposia supported by World Bank projects and United Nations initiatives. The evolution tracked advances in ensemble atmospheric prediction at European Centre for Medium-Range Weather Forecasts, probabilistic forecasting methods from Met Office (United Kingdom), data assimilation techniques from NASA Goddard Space Flight Center, and verification frameworks developed at Royal Netherlands Meteorological Institute, Irish Centre for High-End Computing and Swiss Federal Institute for Forest, Snow and Landscape Research.
HEPEX promotes methods that couple atmospheric ensembles from ECMWF Ensemble Prediction System, Global Ensemble Forecast System, European Flood Awareness System outputs, and regional ensemble systems to hydrological models such as HBV, SAC-SMA, VIC (model), SWAT, WRF-Hydro, Hydrologic Engineering Center's PRMS, RAPID (model), MIKE SHE and mizuRoute. Techniques include ensemble post-processing approaches derived from statistical frameworks used at European Centre for Medium-Range Weather Forecasts and Canadian Meteorological Centre, Bayesian model averaging advanced by researchers at University of Washington and Iowa State University, and data assimilation methods from National Aeronautics and Space Administration collaborations with Jet Propulsion Laboratory. HEPEX integrates remote sensing inputs from Sentinel (satellite constellation), Landsat, Global Precipitation Measurement, SMAP, GRACE, Copernicus Programme and in situ networks like those maintained by Global Runoff Data Centre and United States Geological Survey. Operationalization relies on software ecosystems including OpenDA, DSS (Decision Support Systems), Python (programming language), R (programming language) and platforms used by European Space Agency projects.
HEPEX-driven research supports flood forecasting efforts at European Flood Awareness System, Helsinki Commission, Mekong River Commission, Nile Basin Initiative, Amazon Cooperation Treaty Organization, Mississippi River Commission, International Commission for the Protection of the Danube River, and national services such as National Weather Service (United States), India Meteorological Department, China Meteorological Administration, Servicio Nacional de Meteorología e Hidrología del Perú and Environment and Climate Change Canada. Use cases include reservoir operations practiced by agencies like Tennessee Valley Authority, drought early warning systems used by Famine Early Warning Systems Network, urban flood management in cities linked to United Nations Human Settlements Programme, transboundary water risk assessment handled by International Committee of the Red Cross partnerships, hydropower scheduling with entities such as Itaipu Binacional and China Three Gorges Corporation, and insurance applications involving Munich Re, Swiss Re, Allianz and World Bank catastrophe risk financing.
HEPEX emphasizes verification metrics and protocols informed by verification communities at European Centre for Medium-Range Weather Forecasts, World Meteorological Organization, National Oceanic and Atmospheric Administration and academic centers including University of Reading, University of Colorado Boulder, University of Iowa and University of Bristol. Verification methods include continuous ranked probability score approaches advocated at European Centre for Medium-Range Weather Forecasts, Brier score applications used by Met Office (United Kingdom), reliability diagrams common at Canadian Meteorological Centre, and categorical event-based verification employed in flood case studies analyzed by International Centre for Water Hazard and Risk Management. Intercomparisons occur in multi-model experiments with participants from CNR (Italy), CSIR (South Africa), Korea Meteorological Administration, National Institute of Hydrology (India), Swiss Federal Institute of Technology Lausanne and Tokyo University.
HEPEX operates as a community network with working groups, steering committees and workshops involving organizations such as World Meteorological Organization, European Centre for Medium-Range Weather Forecasts, National Oceanic and Atmospheric Administration, International Association of Hydrological Sciences, Global Water Partnership, European Space Agency, NASA, Japan Meteorological Agency, Australian Bureau of Meteorology, Chinese Academy of Sciences, Indian Institute of Technology, École Polytechnique Fédérale de Lausanne, Max Planck Society, CNRS, CSIC, National Research Council (Italy), Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, Argonne National Laboratory, Princeton University and many national hydrological services and universities worldwide.
Key challenges addressed by HEPEX include integrating climate-scale projections from Intergovernmental Panel on Climate Change assessments with real-time forecasting as done by Coupled Model Intercomparison Project, improving ensemble generation methods used at ECMWF and Global Ensemble Forecast System, quantifying uncertainty propagated from remote sensing platforms like GRACE and SMAP, and ensuring uptake by stakeholders including World Bank, UN Office for Disaster Risk Reduction and regional river commissions. Future directions involve tighter coupling with Earth system modelling pursued by European Centre for Medium-Range Weather Forecasts research programs, expanded use of machine learning developed at Google DeepMind and Microsoft Research, scaling operational systems in partnership with European Space Agency and NASA, and enhancing capacity building through collaborations with International Hydrological Programme and universities such as Harvard University, Stanford University, Columbia University and University of Cambridge.