Global Analysis of Topographic and Climatic Controls on Drainage Basin Shapes.

Drainage basins are fundamental units of Earth's surface, describing how flows accumulate across landscapes. They are direct expressions of how tectonics and climatic forces alter Earth's surface morphology. Here, we measure the width‐to‐length ratios (WLRs) of 386,931 drainage basins (average area ∼157 km2), covering all continents except Antarctica and Greenland. Global variations in WLRs are correlated with climatic aridity, whole‐basin slope, and local topographic roughness. Basins in arid landscapes tend to be narrower, potentially reflecting a higher prevalence of surface runoff and therefore a stronger slope‐parallel component of the transporting flow. Local topographic roughness is associated with wider basins, potentially reflecting greater dispersion of flow directions. Conversely, whole‐basin topographic gradients, potentially reflecting gradients in uplift, are associated with narrower basins. However, steeper basins are also often rougher, so revealing the effects of whole‐basin slope requires correcting for the confounding effects of roughness variations. Plain Language Summary: Drainage basins are essential features that help us understand how water accumulates and flows across Earth's landscapes. In this study, we examined the width‐to‐length ratios of 386,931 drainage basins from all continents except Antarctica and Greenland. We found that basins tend to be narrower in more arid climates. We also observed that, all else equal, basins with greater local roughness tend to be wider, and those with steeper whole‐basin slopes tend to be narrower. Our results thus indicate that on the global scale, basin shapes are strongly influenced by topographic roughness, whole‐basin slope and climatic aridity. Our findings hold across different basin scales, encompassing smaller basins with a mean area of approximately 157 km2 to larger basins with a mean area of around 1,000 km2. These results advance our understanding of global patterns of basin shapes and the tectonic and climatic drivers behind them. Key Points: Globally, basins with greater topographic roughness tend to be wider, and those with steeper whole‐basin slopes tend to be narrowerIn arid regions (aridity index <0.65), basins tend to widen as climate becomes more humidBasin shape is strongly correlated with topographic roughness, whole‐basin slope and climatic aridity on a global scale [ABSTRACT FROM AUTHOR]