Hydrological dynamics of the Cuvette Centrale peatlands: insights from enhanced land surface modeling and SMOS L-band data assimilation

The Cuvette Centrale wetland complex, located in the central depression of the Congo Basin, is a critical component of regional and global carbon and water cycles. The hydrological processes controlling these wetlands, of which 16.8 Mha are classified as peatlands, remain poorly understood, due to complex interactions between the Congo River, its tributaries, variable rainfall patterns, and anthropogenic influences. Here, we address this knowledge gap by interpreting the updates introduced by microwave data assimilation. The employed land surface data assimilation framework follows the setup of the 9-km Soil Moisture Active Passive (SMAP) Level-4 Soil Moisture algorithm that includes a land surface model specifically designed to simulate peatland hydrological processes (PEATCLSM).

First, we update PEATCLSM hydrological parameters for the Congo Basin peatlands, using a new event-based approach named: HYdrological PArameterization of in situ water level dynamics using SATellite-based precipitation (HYPA_SAT). Along with further adjustments to the PEATCLSM module, we significantly reduce the dry bias present in water level simulations with a previous model version. Second, we assimilate L-band brightness temperature (Tb) observations from the Soil Moisture and Ocean Salinity (SMOS) satellite mission for the period 2010 through 2022. We demonstrate that the assimilation of SMOS L-band Tb observations into PEATCLSM further enhances the accuracy of water level estimates, indicated by improved temporal correlations with in situ data. Finally, we present an analysis of the data assimilation state updates, which showed widespread systematic patterns that were linked to observed, but unmodeled, upstream river stage anomalies. The data assimilation results highlight the sensitivity of the hydrology of the Congo Basin peatlands to local and upstream rainfall variability, as well as river dynamics, and thus river management. Therefore, we emphasize the need for integrated hydrological and land management approaches in the peatland region.