Preserving the dominant physical processes in a lumped hydrological model

SummaryThis paper analyses the relationship between the Saturated Area Ratio (SAR) and the Relative Water Content (RWC) within a hydrological catchment. The SAR–RWC relationship is fundamental in lumped modelling in correctly representing the dominant physical processes. According to the simulations provided by a distributed model (TOPKAPI) on several catchments, the SAR–RWC relationship is affected by hysteresis, which is also supported by observations and numerical simulations by other researchers. Due to the strong linearity, this relationship is difficult to derive analytically. In this paper we propose a physical interpretation of the hysteresis and present a methodology to model it. By incorporating this mechanism in a lumped model, we demonstrate improvement in discharge reproduction as evaluated by comparative streamflow simulations.

Research highlights
► We developed a methodology to represent the non linear relationship between the mean soil relative water content (RWC) of a cathcment with the extent of the saturated area (SAR).
► We applied this relationship to the TOPKAPI lumped model and verify that it is able to reproduce the discharge as well as the TOPKAPI distributed mode.
► The TOPKAPI lumped model with the RWC-SAR proposed relationship preserves the values of the main physical parameter i.e. it has the same parameters values of the TOPKAPI distributed model and perfoms equally well without extra calibration.