Hydrological Modeling of a Large Basin:
Application to the French Rhne River
Pierre Etchevers1, Florence Habets1, Eric Martin1, Jol Noilhan1, Catherine Golaz2, Eti-
enne Leblois3, Etienne Ledoux2, Catherine Ottl4, and Daniel Vidal-Madjar4
The goal of the French program GEWEX/Rhne is to develop a method to estimate the hydrological
budget of a large European river using existing datasets. The Rhne basin (86,500 km2) has been
chosen because it presents several interesting features: a strong climatic contrast between the north
part (under oceanic influence) and the south part (under Mediterranean influence), a heavy influence
of the snow on the Alps and Jura mountains river flows, and a limited underground domain. The
strong heterogeneity of the domain is an advantage for the potential climatic applications of the
project because it allows study of a great variety of phenomena and scenarios.
The adopted methodology is based on the use of 4 linked models: the meteorological analysis
system SAFRAN generates the relevant meteorological parameters with the hourly time step at 8 km
resolution by using the observations of the French National Weather Service (Mto-France). The
surface energy and mass fluxes (evapo-transpiration, drainage, and overflow) are calculated by
ISBA, the land surface scheme developed by Mto-France. It uses precise maps of the soil texture
and the vegetation cover (resolution of 2 km). The snow-covered surfaces are specially treated by
using Crocus, a physically based model originally developed for operational avalanche risk fore-
casting. Lastly, the hydrological model MODCOU calculates the water outflow in the soil and the
river flows with a variable spatial resolution depending on the topography (between 1 km and 8 km).
The results obtained with this rather sophisticated tool are presented for a 14-year simulation (from
1981 to 1994) and compared with a rich set of flow measurements (86 hydrographical stations).
Water and energy budgets are studied for some sub-basins of the domain in the light of inter-annual
variability. Particular attention will be paid to the snow cover simulation and its major influence on
the alpine rivers flow.
Mto-France, Centre National de Recherches Mtorologiques, 42 avenue G.Coriolis, 31057 Toulouse Ce-
2 CEMAGREF, 3 bis quai Chauveau, 69336 Lyon Cedex 09, France
3 Ecole des Mines de Paris-Centre d'Informatique Gologique, 35 rue Saint-Honor, 77305 Fontainebleau
4 Centre d'tude des Environnements Terrestre et Plantaires, 10-12 avenue de l'Europe, 78140 Vlizy, France