A New C3S ECV Service for Terrestrial Water Storage and Groundwater

Satellite gravimetry from the GRACE and GRACE Follow-On missions has fundamentally advanced our understanding of the global hydrological cycle. Over the past two decades, these missions have enabled robust scientific assessments of terrestrial water storage and, derived from this, groundwater storage, supporting numerous studies on droughts, floods, and long-term water availability. While the scientific maturity of GRACE-based hydrological products is well established, their systematic translation into operational climate services had yet to happen. Bridging this gap is essential to support climate adaptation and water-related decision-making across societal sectors.

In this contribution, we present the operationalisation of GRACE-based hydrological science into a climate service through the introduction of a new Essential Climate Variable (ECV) Service, “Terrestrial Water Storage and Groundwater”, within the Copernicus Climate Change Service (C3S). The service delivers Climate Data Records (CDRs) for the ECV products Terrestrial Water Storage Anomalies (TWSA) and Groundwater Storage Change (GWSC), designed to meet the requirements of long-term climate monitoring and downstream applications. The datasets, together with a comprehensive Data Documentation Package following C3S standards, are already published or will be made publicly available in the coming weeks.

A central challenge in transforming GRACE-based products into an operational climate service is the assessment and communication of product quality. For global, satellite-derived estimates of TWSA and GWSC, suitable in-situ reference datasets are largely unavailable, particularly at the spatial and temporal scales resolved by GRACE. We therefore developed a dedicated quality assessment framework that combines internal consistency checks, uncertainty characterisation, inter-comparison with independent models and reanalyses, and transparent documentation of limitations and fitness-for-purpose.

The presentation will introduce the new C3S ECV service, describe the delivered datasets and documentation, and focus on the adopted approach to product quality assessment. By doing so, we aim to demonstrate how mature Earth observation science can be translated into an operational climate service that supports adaptation to climate variability and change, while clearly communicating uncertainties to users.