Discharge Estimation via Assimilation of Multisatellite-Based Discharge Products: Case Study Over the Amazon Basin

Emery, Charlotte M. ; Paris, Adrien ; Biancamaria, Sylvain ; Boone, Aaron ; Calmant, Stephane ; Garambois, Pierre-Andre ; Silva, Joecilia Santos Da ; David, Cedric H.

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<p align=justify>River flows are an essential component of the water cycle and are directly accessible for human consumption and activities. River water flux (i.e., river discharge) not only can be measured locally at in situ gauges but also can be estimated at larger scales with the river routing models. However, the number of in situ gauges is declining worldwide while emerging river-related products from satellites are becoming more available. Especially, discharge products based on satellite altimetry water elevations are emerging. These altimetry missions provide different spatial and temporal coverages and may not provide the same amount of information. In this study, discharge products from two satellite altimetry missions (ENVISAT and JASON-2) were assimilated into the large-scale hydrologic model Intéractions Sol-Biosphére-Atmosphére-CNRM's Total Runoff and Integrating Pathways (ISBA-CTRIP) using an ensemble Kalman filter, to correct the simulated discharge. This work investigates whether it is better to assimilate products with a dense spatial coverage but a lower temporal sampling (ENVISAT) or the opposite (JASON-2). Three experiments have been performed: the first two assimilated each product separately, and the last one assimilated the combined product. The open-loop normalized root-mean-square error evaluated against in situ discharge (RMSEn) is 69%. RMSEn is decreased for all experiments. Specifically, it is slightly lower when assimilating ENVISAT-based discharge product (51%) than JASON-2 product (53%) as the ENVISAT-based product spatial coverage is denser. The best results are obtained when both products are assimilated (RMSEn=49%). These results are very encouraging and could be improved when the future Surface Water and Ocean Topography (SWOT) wide swath altimetry mission discharge product will be available.</p>
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