Impact of model structure on flow simulation and hydrologicalrealism: from lumped to semi-distributed approach

Model intercomparison experiments are widely used to investigate and improve hydrological model performances. However, a study based only on runoff simulation is not sufficient to discriminate different model structures. Hence, there is a need to improve hydrological models for specific signatures of streamflow (e.g. low and high flow) and multivariable predictions (e.g. soil moisture, snow and groundwater). This study assesses the impact of model structure on flow simulation and hydrological realism using three versions of an hydrological model called MORDOR: the historical lumped structure and a revisited formulation inflected for lumped and semi-distributed structures. In particular, the main goal of this paper is to investigate the relative impact of model equations and spatial discretization on flow simulation, snowpack representation and evapotranspiration estimate. The models comparison is based on an extensive dataset composed of 50 catchments located in French mountainous regions. The evaluation framework is founded on a multi-criteria split sample strategy. All models were calibrated using an automatic optimization method based on an efficient genetic algorithm. The evaluation framework is enriched by the assessment of snow and evapotranspiration modeling against in-situ and satellite data. The results showed that the new model formulations perform significantly better than the initial one in terms of the various streamflow signatures, snow and evapotranspiration predictions. The semi-distributed approach provides better calibration-validation performances for snow cover area, snow water equivalent and runoff simulation especially for nival catchments.