The influence of climate on the hydraulic geometry of natural river cross-sections

Abstract

Hydraulic geometry is one of the main empirical approaches to understanding the hydraulic adjustments of natural river channels. This study investigates the influence of climate on the exponents of hydraulic geometry (b, f, and m) through the comparative analysis of cross-sections of rivers distributed across five climate groups as defined by the Köppen-Geiger classification: tropical, dry, temperate, cold, and polar. The data were compiled from studies published between 1953 and 2020 and associated with their respective climate domains through spatial cross-referencing of collection points and global climate maps. The analysis was conducted based on b–f–m triaxial diagrams, allowing the evaluation of the hydraulic adjustment patterns of the sections in relation to the theoretical subdivisions associated with width-depth, depth-velocity relationships, Froude number, wetted area, and hydraulic roughness. The results indicate that, despite the marked climatic differences between the analyzed groups, the average structural patterns of the hydraulic geometry are broadly similar. In all climatic domains, a predominance of f > b and values of the exponent m concentrated in the central subdivisions of the diagram were observed, suggesting that climate does not act as a primary controller of hydraulic geometry. Differences between climate groups are mainly manifested in the dispersion of exponents and the occurrence of extreme values, especially in arid, cold, and polar climates, indicating that climate exerts an indirect influence by modulating the variability of hydraulic adjustments, without altering average structural patterns. This study contributes to the understanding of the applicability and limitations of hydraulic geometry as a tool for global comparative analysis, providing support for rapid diagnoses of relative hydraulic stability and for the development of integrated approaches that incorporate hydrological variability, sedimentary connectivity, and local geomorphological controls.