Using GRACE-/FO 10-day CNES solutions for hydrological applications

Abstract

GRACE and GRACE-FO satellite missions measure the spatial and temporal variations in the Earth’s gravity field at a spatial resolution of around 300 kilometers. Unlike most  gravity field products available at monthly resolutions, the CNES produces a 10-day Level 2 solution constrained by Satellite Laser Ranging using Singular Value Decomposition and Tikhonov regularization, improving the estimation of the low- and high-degree spherical harmonics. Resolved up to degree 90 without  spatial filtering, this product enhances the spatial resolution of satellite gravity products. Here, we present the hydrological applications of the Level 3  product, corrected for the missing degree 1 and Glacial Isostatic Adjustment (GIA), representing Terrestrial Water Storage Anomalies (TWSA) expressed in gridded Equivalent Water Heights (mmEWH).This study assesses the added value of the 10-day CNES product for monitoring extreme hydrological events such as droughts and floods based on GRACE-Drought Severity Index (GRACE-DSI). Results show that the 10-day product captures major events like the 2010-2011 La Niña in Australia, and the severe drought that affected France during the 2022 summer. Comparison with the monthly CNES ensemble and daily ITSG-2018 products confirms the strong temporal consistency at seasonal to interannual time scales and substantially higher spatial and temporal resolutions of the CNES 10-day product.GRACE-DSI also shows good agreement with in situ indicators, particularly those integrating information over long time scales, such as the Palmer Drought Severity Index and the Standardized Precipitation Evapotranspiration Index (SPEI). By accounting for the total terrestrial water storage variability, integrated from the surface to deep aquifers, the GRACE-DSI complements indices targeting individual components of the hydrological cycle. The improved temporal and spatial resolution makes the 10-day CNES product and the associated 10-day GRACE-DSI particularly relevant for the monitoring of extreme hydrological events. This study also suggests potential for the preparation of hydrological applications of the future satellite gravimetry missions NGGM and MAGIC, with expected higher spatio-temporal resolution and shorter latency time.