Estimation of river discharge in areas without statistics using SWOT satellite 

Monitoring global river discharge is fundamentally limited by the sparse distribution and ongoing decline of ground-based gauging stations. This observational gap is most critical in "ungauged basins," where lack of data hinders water resource management and flood forecasting. The Surface Water and Ocean Topography (SWOT) satellite mission serves as a transformative solution, providing the first global inventory of Earth’s surface water by measuring river height, width, and slope from space.Estimating discharge from satellite observations is a complex inverse problem because key hydraulic parameters, such as river bathymetry (bottom elevation) and bed roughness, are unknown in ungauged regions. This research explores various advanced methodologies to bridge this gap by integrating satellite-derived measurements of water surface elevation, width, and slope into hydraulic models. These approaches allow for the simultaneous estimation of unknown parameters and river flow, providing a globally consistent, observation-based record of discharge even in basins where ground-based statistics are entirely unavailableThe studies demonstrate that the unique spatial coverage of SWOT allows for a transition from traditional single-point calibration to a "multi-point" parameter selection approach. This strategy uses observations from numerous points across a river network, which significantly improves the model's ability to identify the correct hydrologic parameters compared to relying on a single virtual gauge.While the satellite data contains inherent measurement noise and systematic biases, the spatially distributed nature of the observations helps compensate for these errors. The research indicates that SWOT is particularly effective at resolving temporal variations in discharge, providing a reliable record of hydrologic events even when absolute discharge values carry uncertainty. However, the effectiveness of the mission can be influenced by river "flashiness"—basins with very rapid changes in flow may be harder to characterize due to the satellite's specific overpass timing.SWOT observations provide a vital resource for constraining hydrological processes globally. By enabling the calibration of hydrologic models in previously unmonitored regions, the mission allows for a better understanding of how streamflow responds to rainfall. This capability is expected to lead to transformative science in global hydrology, offering a consistent and observation-based measure of discharge that far exceeds the accuracy of existing uncalibrated global models.