Colin Gleason (UMass Amherst, United States); Cécile Cazals (CNES, France); Michael Durand (The Ohio State University, United States); Stephen Coss (The Ohio State University, United States); Jonathan Flores (UMass Amherst, United States); Merritt Harlan (USGS, United States)

The Surface Water Ocean Topography (SWOT) satellite mission returns terrestrial surface water height, width, and slope, parameters that in turn are used to invert river discharge at a global scale in the Confluence framework. SWOT estimates discharge under two orbits with spatial and temporal tradeoffs: the initial, semi-global, 90-day 'Fast Sampling Orbit' (‘FSO’) from April to August 2023 and the primary, global, 21-day cycled 'Science Orbit' (‘SO’) from mid-August until end of lifetime. The reaches included in both orbits provide an opportunity to assess SWOT global discharge performance between orbits and its capabilities for discharge regime capture in both gauged and ungauged basins at a hydrologically relevant timescale. To characterize temporal sampling effects on river discharge characterization, we ran the Confluence framework ‘offline’ on all 22,777 FSO reaches. We tested discharge performance reaches from FSO only, SO only, both continuous orbits (‘continuous’), and FSO sampled like SO (‘sampled’) in time for these reaches to isolate the effect of the orbit, focusing especially on hydrologic regime capture as well as variability during the April-July FSO time period. While all configurations generally show low bias and evenly distributed global discharge differences, the FSO alone slightly underestimates discharge at any magnitude compared to ‘continuous’ data especially in Arctic regions whereas SO only data overestimates low discharge and underestimates high discharge especially in Arctic regions compared to ‘continuous’ data.