Lake Morphometry Influences the Accuracy of SWOT Estimates of Water Level

Accurate assessments of surface water resources are vital as climate change reshapes the hydrological cycle and intensifies pressure on freshwater availability. The Surface Water and Ocean Topography (SWOT) mission delivers transformative measurements of water-surface elevation (WSE), yet lake morphology may influence accuracy. Here, we compared SWOT-derived WSE with gauge records from 62 Swedish lakes to test whether circularity, elongation, compactness and lemniscate index affect performance. First, we find that SWOT meets its design specification for lakes ≥ 1 km² (median RMSE = 10.04 cm) and maintains acceptable accuracy for smaller lakes (median RMSE = 19.1 cm). Second, we find that circularity, elongation and compactness are correlated with the RMSE. Finally, we find that after a multilinear regression, shoreline morphology accounts for 29% of the residual error. These findings demonstrate that shoreline morphology, not only lake size, influences SWOT accuracy and should be considered in uncertainty models and mission performance evaluations.