The use of topographically-enhanced catchment descriptors to improve the predictions of streamflow events characteristics across German catchments

Catchment descriptors are standard explanatory factors for catchments hydrological signatures, they are widely used to infer dominant hydrological processes, identify and transfer information across similar catchment, and upscale findings from smaller to larger scales. However, conventional approaches for deriving catchment descriptors use spatial averages over the catchment, that overlook the inherent spatial variability arising from geomorphological catchment organization. This could explain the limited accuracy of existing models to predict hydrological responses across catchments. In this study, we examine the potential of topography to capture the spatial variability of catchment descriptors. We weight various catchment descriptors with four topographic metrics reflecting distinct aspects of spatial variability, namely, horizontal channel proximity (distance to nearest drainage), vertical drainage potential (height about the nearest drainage), flow-path length (distance to outlet), and river network hierarchy (stream order). We test their added value of the enhanced descriptors to predict mean values and variability of streamflow event characteristics (event runoff coefficient, time scale, rise time) in 392 German catchments.

Results show considerable improvement in prediction accuracy of mean event rise time and time scale using catchment descriptors weighted with distance to the nearest drainage and outlet compared to standard averaged descriptors. The proximity to the drainage that effectively controls the travel time likely to exert a strong control of shape and timing of event hydrographs. The prediction of the variability of event runoff coefficient improved considerably using when descriptors weighted with height above the nearest drainage. The latter effectively captures the soil moisture levels and channel saturation that likely controls the variability of runoff coefficients. However, predictions of the mean runoff coefficient, and variability of event time scale and rise time exhibited minimal gains. This indicates that these characteristics are rather governed by the climate and soil properties at larger scale, while their smaller scale variability plays only minor role. These findings demonstrate how topographic metrics serve as effective proxies for catchment geomorphological organization. The derived topographically-enhanced catchment descriptors have potential to improve predictions of hydrological signatures