Coupling the ISBA Land Surface Model and the TOPMODEL Hydrological Model for Mediterranean Flash-Flood Forecasting: Description, Calibration, and Validation

Béatrice Vincendon,Eric Martin,Florence Habets,Georges-Marie Saulnier,Joel Noilhan,Katia Chancibault,Ludovic Bouilloud,Sandrine Anquetin,Véronique Ducrocq

doi:10.1175/2009jhm1163.1

Abstract

Abstract Innovative coupling between the soil–vegetation–atmosphere transfer (SVAT) model Interactions between Soil, Biosphere, and Atmosphere (ISBA) and the hydrological model TOPMODEL has been specifically designed for flash-flood forecasting in the Mediterranean area. The coupled model described in this study combines the advantages of the two types of model: the accurate representation of water and energy transfer between the soil and the atmosphere within the SVAT column and an explicit representation of the lateral transfer of water over the hydrological catchment unit. Another advantage of this coupling is that the number of parameters to be calibrated is reduced by two, as only two parameters instead of four parameters concern the TOPMODEL formulation used here. The parameters to be calibrated concern only the water transfer. The model was calibrated for the simulation of flash-flood events on the three main watersheds covering the French Cévennes–Vivarais region using a subset of past flash-flood events having occurred since 2000. The complementary subset of flash-flood events was then used to carry out an objective verification of the coupled model after calibration. The evaluation on these six independent past flash-flood events shows satisfactory results. The comparison of the observed and simulated hydrographs demonstrates that no flash-flood peaks are missed. Relevant information for flash-flood forecasting can always be inferred from the simulations, even for those with quite poor results, making the system useful for real-time and operational flash-flood forecasting.

Highlights

The western Mediterranean region is regularly affected by devastating flash-flood events, during autumn
Coupling between the soil–vegetation–atmosphere transfer (SVAT) model ISBA and the hydrological model TOPMODEL has been designed. This coupled model allows the advantages of the two types of models to be combined: the accurate representation of water and energy transfer between the soil and the atmosphere within the SVAT column and an explicit representation of the lateral transfer of water over the hydrological catchment unit
We go one step further than previous studies in the way the TOPMODEL concepts are introduced in a SVAT model

Summary

Introduction

The western Mediterranean region is regularly affected by devastating flash-flood events, during autumn. We chose to vary f from 1 to 4 by 1 m21 steps and a from 0.25 to 1.5, by steps of 0.25, to stay close to the values given in Decharme et al (2006) for the same region with the ISBA model The discharge dynamics was not well simulated and was comparable to the one obtained with the SAFRAN rainfall (Fig. 6) These results confirmed that a large accumulated period for rainfall was not able to capture the rapid time evolution of the heavy precipitation event and the evolution of the flash-flooding event. The tests described confirm that the sensitivity to the input rainfall field, in terms of both spatial and temporal distribution, is still high when the coupled system is used

Model evaluation

Findings

Conclusions and discussion