Catchment response times – understanding runoff dynamics from catchment distances and celerities

ABSTRACT In this study we explore how varying the river network (RN) density affects the distribution of hillslope to RN distances, the subsurface water celerities and hence the response times. Eleven Norwegian catchments (with areas of 0.007 to 500 km2) were used for the analysis, and the Distance Distribution Dynamics (DDD) hydrological model was calibrated for each catchment and RN. Equally good Kling-Gupta efficiency scores suggest a degree of equifinality in that many constellations of RNs and subsurface celerities have equally good model performance. All catchments display a linear relationship between the calibrated mean subsurface water celerity and mean hillslope to RN distance, consistent with a constant mean response time (MRT). The MRTs vary from 1 to 49 days for the different catchments and agree with MRT estimated from recession analysis and regionalized through regression and catchment characteristics. The latter aids in the estimation of model parameters for ungauged basins.