Some hydrological challenges in understanding discharge generation processes in the Rhine and Meuse basins

Although societal hazard related to hydrological events has increased dramatically over time, our understanding of the discharge generating processes is still deficient. The main challenges appear to be related to the scale of the processes. Hydrological processes are highly heterogeneous, non-linear and interconnected. Upscaling from micro- to catchment scale and subsequent parametrisation appears undoable because of data requirements, model complexity, computational time requirements, and equifinality (implying that different combinations of parameters generate equally good results). A new generation of hydrologists is looking for answers to match the observed complexity at the plot-scale, with the apparent simplicity that arises at the catchment scale. One of the key processes in the watersheds of the Meuse and Rhine is the rapid sub-surface flow, a process which is still poorly understood.