the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Sep 2026
Operational Earth system hydrology at ECMWF
Abstract. The representation of river routing and floodplain dynamics remains a key limitation in many global Earth system and numerical weather prediction models, despite their importance for hydrological extremes, water resources, and land–atmosphere interactions. This paper presents the implementation of a global hydrodynamic river routing capability within the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) through the integration of the Catchment-based Macro-scale Floodplain (CaMa-Flood) model into the ecLand land surface scheme.
The system enables the routine simulation of river discharge, water level, and inundation extent within a physically consistent Earth system modelling framework. We describe the scientific design and technical developments required to transition from research to operational implementation, including coupling strategies, state initialisation, parallelisation using a basin-based hybrid MPI/OpenMP approach, and integration within ECMWF's Research-to-Operations workflow. The implementation maintains consistency across multiple configurations, from offline experiments to fully coupled forecasts, while preserving operational constraints such as computational efficiency and forecast stability.
The added value of the integrated system is demonstrated through a range of applications, including global water resources monitoring contributing to the World Meteorological Organisation State of Global Water Resources Report, real-time ensemble flood forecasting, high-resolution regional simulations, and land-surface diagnostics. Results illustrate that river discharge provides a powerful integrative constraint on the land water cycle and supports the identification of model deficiencies in hydrological processes. The system also enables the generation of continuous, global, high-frequency hydrological datasets suitable for both operational applications and emerging data-driven modelling approaches.
This work establishes a new capability for global hydrological prediction within an operational Earth system model and provides a framework for future developments toward fully coupled atmosphere–land–river interactions.
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Status: open (until 30 Oct 2026)
- RC1: 'Comment on egusphere-2026-4305', Toby Marthews, 25 Sep 2026 reply
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RC2: 'Comment on egusphere-2026-4305', Jan Polcher, 01 Oct 2026
reply
Review in attached document.
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RC3: 'Comment on egusphere-2026-4305', Fitsum Woldemeskel, 13 Oct 2026
reply
General comments:
The manuscript presents the integration of global hydrodynamic river routing model, CaMa-Flood, within the ECMWF Integrated Forecasting System (IFS). The paper also offers a valuable account of the scientific and technical steps required to transition experimental research to operation system. Overall, the manuscript is well written and makes a meaningful contribution, however, I have few specific comments that could further strengthen the paper, as follows.
Specific comments:
- While the manuscript focuses on the design and technical developments, a robust assessment of model outputs, particularly discharge and flood inundation is missing other than application for selected case studies. This would be valuable to provide greater confidence in the forecast performance in different regions of the world. Such analysis would also help identify areas of strength and weakness of the modelling/forecasting system.
- In addition, the statement in line 585 that the flood forecast is 'realistic' requires further justification. It appears there is a noticeable timing error in Figure 7d-f. The model also underestimated the subsequent event that peaked around 10/11 February. The authors should discuss these and provide potential explanations for the forecast discrepancies. I think adding the rainfall forcing would shed some light about this.
- Further clarification of how the flood categories (minor, moderate, major etc) are defined in Figure 7 is required. For example, in Australia where the case study is conducted, flood categories are typically defined based on impacts rather than exceedance probabilities. Therefore, a discussion of the rational behind the approach and how this translates to local emergency management authorities would be beneficial.
Citation: https://doi.org/10.5194/egusphere-2026-4305-RC3
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The authors are reporting the results of a process whereby they are introducing a new capability for global hydrological prediction within the operational Earth system model IFS (the Integrated Forecast System). Coupling together a sophisticated river hydrodynamics model like CaMa-Flood with a robust and well-tested land surface model like ecLand within a wider Earth System Model framework like IFS is a challenging undertaking and represents a significant step forward. It is fantastic to learn that this process has been completed at ECMWF and it is a credit to the hard work of all the authors listed - and many more - who have worked on it.
This work represents a substantial contribution to modelling science because there are very few coupled modelling systems of this type available to researchers or policy-makers. A spatially-consistent prediction system like the updated IFS will be of significant interest in many contexts because being able to predict reliably water cycle quantities is fundamental to planning and management of water resources in both water-poor (often drought affected) and water-rich (often flood-affected) parts of the world.
Specific comments: Several case studies are presented and discussed in depth (Global 2024, Burdekin 2025, Zambezi 2023 and Indus 2022). These represent very in-depth summaries of directly relevant studies in a variety of large catchments around the world, demonstrating the usefulness of the IFS tool in contrasting environments. Each one shows different aspects of what is now possible using IFS and I believe will be of great use for future workers who will be able to refer back to these as standard analyses.
The paper is very professionally written. The description of the release curation cycle and version control systems that have been developed at ECMWF during this effort is interesting and it gives a great insight into the complexity of such an undertaking and the many levels of checks and validations that are required to make sure that the result is operationally capable.
Technical corrections: None