From GRACE Science to Climate Service: Operational TWSA and GWSC Products in the Copernicus Climate Change Service (C3S)

Abstract

Over nearly 25 years, GRACE and GRACE-FO have matured from a novel observing system into an operational-grade data source, with terrestrial water storage anomaly (TWSA) and, derived from this, groundwater storage change (GWSC) products now feeding directly into drought, flood, and water-availability assessments. Despite this maturity, systematic translation of GRACE-based TWSA and GWSC into a sustained, standards-compliant climate service has so far been missing. This gap has limited uptake by climate adaptation and water-management communities which rely on Essential Climate Variable (ECV)-type products with defined uncertainty and provenance.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 TWSA and GWSC, built to C3S CDR requirements for homogeneity, traceability, and long-term consistency. The datasets, together with a comprehensive Data Documentation Package following C3S standards, are published on the Climate Data Store (CDS).A key challenge in this operationalisation is quality characterisation in the near-absence of suitable in-situ reference data at GRACE's native spatial and temporal resolution. We address this with a dedicated quality assessment framework combining internal consistency checks (e.g., mass conservation, basin-scale closure), inter-comparison with global hydrological models and land-surface/reanalysis products, and the explicit documentation of known limitations and fitness-for-purpose. Additionally, TWSA is compared against independent mascon and spherical-harmonic solutions and GWSC against regionalised in-situ measurements from groundwater boreholes.As the C3S strives towards more accessible information for the public and decision makers, both products contribute to Climate Intelligence efforts through a variety of visualisations across different time scales, which will also be presented here.