Expanding SWOT-derived river discharge time series through leveraging river network topology and regionalization

It is often assumed discharge upstream and downstream of a river location are highly correlated and can be transferred between locations using a scaling factor like the drainage area ratio between locations. However, urbanization and instream infrastructure impact this assumption. This is especially important for the upcoming Surface Water and Ocean Topography (SWOT) mission, which will observe water surface elevations, extents, and slopes for rivers wider than 50-100 meters using a 21-day orbit, providing river reach derived discharges that are not uniform in time and not coincident with derived discharges of many upstream/downstream reaches. Here, the applicability of the drainage area ratio method to integrate, in space and time, SWOT-derived discharges throughout the observable river network of the Mississippi River basin is assessed. In some cases, area ratios ranging from 0.01 to 100 can be used, but cumulative urban area and/or the number of dams/reservoirs between locations decrease the methods applicability. Though the mean number of SWOT observations for a given reach increases by 83% and the number of peak events captured increases by 100%, expanded SWOT sampled time series distributions often underperform compared to the original SWOT sampled time series for significance tests and quantile results. Alternate expansion methods may be more viable for future work.