Exploring the impact of the temporal resolution of satellite gravity products on hydrological Data Assimilation (DA)

Terrestrial Water Storage (TWS) derived from the GRACE and GRACE-FO satellite gravity missions has been used in the past to improve the water storage representation of large-scale hydrological models through state-of-the-art sequential Data Assimilation (DA). These past experiments often used monthly gravity solutions, whose temporal resolution is not short enough to capture sub-monthly and fast-evolving hydrological processes such as floods. The future gravity missions, i.e., ESA’s NGGM (a single low-low satellite-to-satellite, ll-sst, gravity mission on an inclined orbit) and MAGIC (a double ll-sst gravity mission including NASA/DLR’s GRACE-C and ESA’s NGGM), are designed to provide gravity solutions with 5-day and monthly temporal resolutions with short latency. Their spatial resolution is expected to be better and their uncertainty smaller than the GRACE-type gravity missions. Therefore, in this study, we will evaluate the added value of the NGGM and MAGIC missions in hydrological DA applications, especially for simulating water storage and river discharge during sub-weekly and sub-monthly flooding events. This assessment is important to understand the role of the NGGM and MAGIC products in future operational flood prediction systems. Our experiments will be performed using the daily 0.1° resolution W3RA water balance model, forced by the ERA5 climate inputs, during floods in the Brahmaputra and Danube River Basins. As observations, 5-day and monthly GRACE-C-like, NGGM-like, and MAGIC-like TWS estimates will be used. The full error covariance matrix information of the observed TWS will be considered during the DA experiments, which are the outputs of closed-loop simulations of the ESA SING project, considering both instrumental and dealiasing errors. Validations will be performed against synthetic hydrological water storage and river discharge time series that are used to generate the hydrological truth.