Evaluating the potential of reach water surface elevation product from the SWOT mission in assimilated hydrodynamic modelling.

Spatiotemporally consistent quantification of river discharge is a persistent problem in the field of hydrology. The current generation of technologically advanced satellite sensors provide reliable alternatives to the conventional gauge monitoring system. In this study, we utilize the Water Surface Elevation (WSE) measurements from the recently released river products from the Surface Water and Ocean Topography (SWOT) mission. We integrate the reach WSE measurements into a distributed hydrodynamic model through an assimilation system to study its contribution towards enhancing the modelled hydrodynamic variables over an entire river basin. Assimilation is implemented using both synthetic and real SWOT reach WSE measurements, where the former is generated using a new method involving the CNES Large Scale SWOT Hydrology Simulator and the NASA Jet Propulsion Laboratory’s (JPL) RiverObs toolkit. The study using synthetic data is conducted for a 3-year period, whereas that using real measurements are implemented based on the availability during the science phase of the mission. Real measurements from the SWOT mission are affected by the presence of outliers that are filtered prior to assimilation to ensure consistent improvements in the output variables corresponding to each satellite overpass date over the study region. SWOT reaches are accurately connected to the river network grid before initiating the assimilated model run. Results reveal notable improvement in modelled discharge after assimilation, with the NSE values exceeding 0.6 and 0.4 for the synthetic and real SWOT data-based experiments, respectively. The improvements, though pronounced towards the downstream reaches, are evident at all validation stations across the basin.