How can rainfall-runoff models handle intercatchment groundwater flows? Theoretical study based on 1040 French catchments

This paper examines the possible solutions that may allow a rainfall-runoff model to cope with the existence of unknown intercatchment groundwater flows over a given catchment. On the basis of a large catchment set we compare four versions of the GR4J and the SMAR rainfall-runoff models that differ in the way they use one of their parameters to adjust catchment-scale water balance. We show that from both the hydrological likelihood and the modeling efficiency point of view it is preferable to explicitly represent intercatchment groundwater transfers. The surrogate corrective solutions tested in this paper (correcting or scaling factors applied to the climatic input data or to the catchment area) that are sometimes used in practice could be used on the sole grounds of streamflow simulation efficiency, but we show that they should be avoided since they may lead to obviously unrealistic corrections and consequently yield a similarly unrealistic distribution between evaporation streamflow and underground fluxes.