Coupling of TRAIN and ZIN

As TRAIN simulates rather long term fluxes between soils, vegetation and atmosphere it is an ideal supplement to ZIN, which concentrates on short term runoff generation processes. The coupling layer of both models is the soil storage. Here a “dynamic” coupling is envisaged with a flexible time step of modelling which is adopted to periods of rain and no-rain. During times of rain the field-based runoff generation routine of the ZIN model is active describing the filling of the soil storage (field derived infiltration functions) and overland flow generation by Hortonian or saturation excess runoff. The temporal resolution will be at its maximum (5 minutes) using all information of the radar data. Certain modules of TRAIN will be de-activated (e.g. evapotranspiration, which is negligible during rainfall). The generated surface runoff will be concentrated, and routed through the channel network by ZIN accounting for surface reservoirs and channel transmission losses. During times of no-rain the soil module of TRAIN is active emptying the soil storage by evapotranspiration. These calculations are important for modelling the next event, as they describe initial filling of the soil storage. SVAT-processes do not need the high temporal resolution of hydrological runoff generation, which means that at that time a 1h time step will suffice. As such TRAIN provides the missing long term soil moisture reduction terms to ZIN which changes the single event model ZIN to a combined model that can be run on a continuous mode. On the other hand the runoff generation, concentration and routing routines of ZIN provide hydrological components additionally to TRAIN making the combined model two-dimensional accounting for lateral fluxes and spatial concentration of water resources important for water management.

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