Authors: David Baude, Rebecca Diehl, Ijaz Ul Haq, Kristen Underwood, Alexander Prescott, and Beverley Wemple – University of Vermont; Belize Lane and Colin Phillips – Utah State University
Title: Spatial and Temporal Variability in Global River Slopes from the Surface Water and Ocean Topography (SWOT) Satellite
Presentation Type: Poster Presentation
Abstract: River water surface slope (WSS) is fundamental for hydrologic, hydraulic, and geomorphic modeling. Unlike channel bed slope, often treated as short-term stationary, WSS varies dynamically as flow interacts with bed heterogeneity. We analyze global spatial and monthly patterns of WSS using the SWOT Level 2 River Single-Pass Vector data (within 2023/08 – 2025/05). Both hemispheres show significant monthly differences: WSS is generally higher in winter and lower in summer, likely due to higher discharge and stage during typical events that flatten the water surface, and low-flow winters where rugged bed topography exerts stronger control.
Month-to-month changes are larger during winter than summer. Despite temporal variability, spatial patterns remain strongly tied to topography. Monthly WSS coefficient of variation is strongly negatively correlated with median WSS (a topographic-slope proxy), indicating flatter rivers have higher WSS variability. These results clarify large-scale water surface dynamics and motivate testing temporal WSS in hydrologic and hydraulic models.