The C3S Water Service: Operational seasonal forecasts and climate change projections co-developed for the water sector

The Copernicus Climate Change Service (C3S) Water Service is an operational hydrological information system delivering authoritative water and hydroclimate information at European and global scales, spanning current conditions, seasonal forecasts, and long-term climate projections. Commissioned by ECMWF on behalf of the European Commission, the C3S Water Service supports climate change adaptation and resilient water management across sectors by delivering data via interactive web applications and the Copernicus Climate Data Store (CDS). The service is delivered by a consortium of European research centres, universities and operational hydrometeorological organisations, ensuring rigorous scientific underpinning while promoting operational sustainability and user-oriented design.  

The operationalisation of the C3S Water Service advances beyond experimental prototypes, engaging users to co-develop and deliver timely, quality-controlled hydrological information at global and regional scales. Meeting universal user needs, it provides variables such as river discharge, soil moisture, runoff, and snow water equivalent, alongside specific indicators defined by users, tailored to their sectors. This supports operational decision-making for flood and drought risk, water resources planning, and climate risk assessments.  

The C3S Water Service adopts a multi-model ensemble framework, enabling a seamless service from seasonal outlooks to multi-decadal assessments and climate projections. Consistent re-gridding and bias adjustment are applied to the climate input data for both the seasonal forecasting system and the hydroclimate projections production. The seasonal forecast models currently used are the ECMWF SEAS5 model and CMCC-SPS3.5, with the inclusion of more systems planned over the coming years. For climate projections, a selection of members from the CMIP6 ensemble is used for the Global domain, and CMIP6 EURO-CORDEX members for the European domain. The hydrological models ECLand, HYPE, JULES, LISFLOOD, mHM, PCR-GLOBWB and VIC-WUR are applied consistently across both time horizons at a resolution of 5 km over Europe, and 0.1 deg. (approximately 10 km) globally. In addition, the service provides the processed meteorological forcing data, allowing future inclusion of additional hydrological models with minimal effort. 

Critically, the C3S Water Service is founded on an iterative development and community engagement strategy to refine product scope, improve usability, and co-develop applications that meet evolving scientific and operational needs. Through ongoing workshops, user forums, and collaborative research activities, we invite hydrologists, hydroclimate modellers, data scientists, water practitioners, and policy makers to contribute insights, test emerging products, and shape the future trajectory of the service.