CHYM: A Grid based Hydrological Model

Watershed management and early warning flood forecasting system is becoming more and more important especially in relation to anticipated climate change. The characteristics and the validation of the Cetemps HYdrological Model (CHYM) developed by the hydrological group of the Cetemps Center of Excellence are described. CHYM is a grid based model and the main physical processes concerning the hydrological cycle are implemented in the model (Todini and Ciarrapica, 2002; Sorooshian et al., 1995). In the preprocessing phase different data sources are assimilated by the model in order to reconstruct precipitation field on the area of interest. At the moment the available data are the observed rain gauge values, the forecasted MM5 precipitation fields and the satellite rainfall estimation (Grimes et al., 2003). This multisources data acquisition system using observed and forecasted data makes it possible to simulate a time window that span from few days before the event to few days after. At each time step data from different source and with different spatial distribution are merged using a cellular automata based algorithm. The possibility to use MM5 data makes also the model suitable for climate change impact assessment. The model can be run with any spatial resolution up to 300 meters and in any spatial domain defined over the Italian area. Using the Digital Elevation Model (DEM), several flow check tests have been performed to verify how the drainage network is simulated in a realistic way for the main Italian river basins. The validation of the river flow against observed data is being performed and in the near future an evaluation of the model performances during the main flood events in the Italian area has been planned.