The Potential of SWOT River Discharge Estimates to Constrain Hydrological Processes Globally in Ungaged Basins

Remote sensing of hydrology provides the key to one of the longest-standing problems in hydrology: ungaged basins. The global network of river discharge measurements available publicly accurately captures overall streamflow into global ocean, but coverage for smaller tributaries upstream, is vanishingly small. The forthcoming Surface Water and Ocean Topography (SWOT) mission will vastly expand measurements of global rivers. However, converting the SWOT measurements of height, width and slope into river discharge is non-trivial. SWOT discharge algorithms will provide discharge for all SWOT-observed rivers, but at lower accuracy than what is possible at a gage. In this paper, we answer the question of where and how SWOT discharge will be valuable. We show that median river discharge accuracy will be on the order of 50%, in terms of normalized root mean squared error (nRMSE), whereas unbiased nRMSE will be on the order of 10-20%. We discuss how SWOT discharge will contribute to global hydrologic science in the coming decade.