The (ir)relevance of plot- and hillslope scale processes for catchment runoff

Experimental field studies are crucial to understanding hydrological processes. Studies at the plot-, hillslope-, or small catchment-scales have helped us to understand how water flows toward the stream network of larger catchments. However, little of this detailed knowledge is used in hydrological models because the calibration of simple models already leads to good runoff simulations. Furthermore, not all hillslope locations contribute equally to catchment runoff and in some cases, hillslopes or specific hillslope locations may seem irrelevant for the catchment scale runoff response, at least until a certain threshold is crossed. It is essential to consider these thresholds because climate or land use change may cause them to be passed more frequently in the future, so models based on historic runoff data might no longer accurately predict the catchment runoff response. In this talk, I will provide examples of such thresholds and discuss the need to consider connectivity between landscape elements when interpreting the streamflow or stream chemistry response at the catchment scale. In doing so, I will highlight the need to understand hydrological processes at the plot and hillslope scales for predicting catchment-scale runoff, even if these processes may seem irrelevant at first.