Adapting the coupled hydrological model ISBA-TOPMODEL to the long-term hydrological cycles of suburban rivers: Evaluation and sensitivity analysis

The hydrological model ISBA-TOPMODEL, initially developed for large rural basins prone to flash floods, has been adapted to suburban basins. Impervious surfaces were taken into account assuming very low infiltration, production of runoff drained through the sewer network when the maximal surface stock capacity is exceeded and groundwater infiltration. This model was evaluated on a French basin, located in the northwestern France, within a suburb of the city of Nantes. A sensitivity study was first performed on the major urban parameters in order to determine which ones had to be calibrated. A ten-year period (2001–2010) was simulated, with the first three years for calibration purposes and the last seven for the actual evaluation. The statistical criteria reveal that the model tends to underestimate total discharge during dry periods while it overestimates discharge during wet weather. The underestimation seems to be caused by an unrealistic deep drainage through the soil, whereas the overestimation can be attributed to impervious surface runoff overestimation. Nevertheless, over the entire simulated period, the statistical criteria still indicate satisfactory results.