Does Catchment Nestedness Enhance Hydrological Similarity?

The topology of river networks defines the hierarchical organization of the landscape and controls the drainage pathways triggered by precipitation. This study investigates how the structure of channel networks influences spatial patterns of flow regimes by focusing on the hydrograph observed at the outlet of nested and non-nested basins. An extensive data set spanning diverse geomorphoclimatic conditions is used to show that – when inter-catchment distance increases – nested catchments exhibit a more pronounced decrease of streamflow correlation as compared to non-nested sites. Thus, non-nested basins have more correlated hydrologic responses at large distances. This unexpected behavior is explained by a geometrical model, which reveals that inter-catchment differences in size and elevation are larger in nested sites, thereby increasing the spatial heterogeneity of key hydrological processes that shape the hydrograph. This study provides clues to critically reinterpret the hydrological response on nested versus non-nested catchments, with relevant implications for hydrology and ecology.