Quantifying Climatic Controls on River Network Branching Structure Across Scales

摘要

The branching structure of river networks is an important topologic and geomorphic feature that depends on several factors (e.g., climate and tectonics). However, mechanisms that result in such branching patterns in river networks are poorly understood. Observations from natural catchments have revealed controls of climate on drainage density (D-d). In this study, we investigate the effects of climatic forcing on river network topology and geometry beyond D-d. For this, we selected 26 basins across the United States with equal D-d, however, different climate aridity index (defined here as the ratio of mean annual potential evaporation to precipitation). The river networks of these basins were extracted, using a curvature-based method, from high-resolution (1-m) digital elevation models, and several metrics such as width functions, branching angles, and side branching ratio were computed. We used a multiscale entropy approach to quantify the geometric and topologic irregularity and structural richness of these river networks. Our results revealed the systematic impacts of climate forcing on the structure of river networks. We showed that the width functions of dry basins have higher entropy as compared to those of humid basins across spatial scales. Higher entropy suggests more heterogeneity in drainage network of dry basins. This heterogeneity is manifested in channels and their junctions resulting, on an average, in larger junction angle and longer channel links in dry basins compared to humid basins.