Quoted from: www.umr-cnrm.fr/spip.php?article274 

TOPMODEL (TOPopgraphy based hydrological MODEL, Beven and Kirkby 1979) is a distributed hydrological model. It stands on the idea that flood generation is mostly controlled by saturation excess runoff. TOPMODEL makes use of the hillslope topographical properties to deduce the soil water contents spatial distribution within a watershed. The latter is described through a Digital Elevation Model (DEM) and the soil moisture of each DEM pixel depends on both the spatial distribution of a hydrological similarity index and the mean storage deficit over the catchment.

A version of TOPMODEL has been adapted to the Mediterranean flash-floods context, It is called TOPODYN . Some experiments performed within the French Cévennes-Vivarais Mediterranean Hydrometeorological Observatory (http://www.lthe.hmg.inpg.fr/OHM-CV/) proved the usefulness of coupling land surface models and hydrodrological models for Mediterranean floods simulations .

So CNRM-GAME together with the hydrological community developped a coupling between ISBA and TOPODYN. This coupling consists in introducing into ISBA a lateral soil water distribution following TOPODYN concept. The soil-atmosphere interface is managed by ISBA, especially for evaporation and soil infiltration. Then the ISBA soil moisture fields are modified through TOPMODEL lateral transfers based on topographical information. From the new saturated areas and new soil moisture fields obtained, ISBA computes sub-surface runoff and deep drainage which are routed to the watershed outlets to produce total discharges.

The ISBA-TOP coupled system is used at CNRM for Mediterranean flood simulation and forecast. The first version of ISBA-TOP was based on the ISBA-3L version. ISBA-TOP has been calibrated for several Mediterranean watersheds, it has been run in real time within HyMex special observing periods on 4 watersheds in the Cévennes-Vivarais region as well as 3 watersheds in the Provence area. Case studies has been conducted also on Spanish and Italian catchments.

This ISBA-TOP version is used in operations in NIMH, the hydrometeorological service of Bulgaria for the Arda River flood forecasting. (Artinyan et al, 2016).
Since 2015, ISBA-DF version is available for ISBA-TOP coupled system. This allows the model to be fully parametrized and to run without any calibration. Edouard et al, 2016 designed a probabilistic version of ISBA-TOP which accounts for the uncertainty that affects the model hydrodynamical parameters and the soil moisture initial conditions.
ISBA-TOP does not only allow the simulation of river discharges but also of intense runoff phenomena. This is crucial for impact studies such as road cuts triggering for instance (Vincendon et al., 2016).

References :

Artinyan, E., Vincendon, B., Kroumova, K., Nedkov, N., Tsarev, P., Balabanova, S. and Koshinchanov, G. : Flood forecasting and alert system for Arda River basin, Journal of Hydrology, in press.

Beven K. and Kirkby M.J., 1979 : A physically based, variable contributing area model of basin hydrology. Hydrol. Sci. Bull., 24, 43-69.

Bouilloud, L., K. Chancibault, B. Vincendon, V. Ducrocq, F. Habets, G.-M. Saulnier, S. Anquetin, É. Martin, J. Noilhan, 2009: Coupling the ISBA land surface model and the TOPMODEL hydrological model for Mediterranean flash-flood forecasting: Description, calibration and validation. Journal of Hydrometeorology, 11(2), 315-333

Edouard S., Vincendon B. and Ducrocq V : Taking hydrological uncertainty into account in flash flood forecasting, Journal of Hydrology, in preparation.

Pellarin T., G. Delrieu, G.M. Saulnier, H. Andrieu, B. Vignal and J.D. Creutin, 2002: Hydrological visibility of weather radars operating in mountainous regions: case study for the Ardèche catchment, France, J. Hydrometeorol. 3 (5) , pp. 539–555.

Vincendon B., Ducrocq V., Saulnier G.M.; Bouilloud L., Chancibault K., Habets F., Noilhan J., 2010 : Advantages of coupling the ISBA land surface model with a TOPMODEL hydrological model dedicated to Mediterranean flash floods, Journal of Hydrology, doi:10.1016/j.jhydrol.2010.04.012.

Vincendon B., Edouard S., Dewaele H., Ducrocq V., Lespinas F., Delrieu G., Anquetin S. : Modeling flash floods in southern France for road management purposes, Journal of Hydrology, under review.