Abstract : 3N.4
Statistical estimation of precipitation over french mountain ranges

Frédéric Gottardi, Emmanuel Paquet, Charles Obled, Joël Gailhard
Direction Technique Générale - EDF

The estimation of snow packs and precipitations in mountainous areas - which are very important for the managers of a hydropower electricity producer like EDF – are still today quite uncertain. EDF-DTG is developing tools for the interpolation of precipitations, in order to be able to provide an estimate of precipitations in any point of mountainous areas. The developed tools are essentially based on the ground sensors network of DTG, which measures precipitations and snow in French mountains.

The hydrology team of EDF-DTG is working on the development of a tool for precipitation interpolation in mountainous areas. It hopes to progress toward daily or « evenement » maps of precipitations and snow cover maps, based on the hydrological basins, which are subject of an operational hydrological forecast.

In order to develop this model, a very large database was built for the french mountains, containing french data but also swiss, italian and spanish data. This model is based on a Digital Elevation Model with a mesh of 1´1 km. On each pixel, a local linear relation between precipitations and altitude models the orographical effect, which is considered the effect dominating in the explanation of precipitations in mountainous areas. This relation is established with a linear regression on a local group of points of measurement near the considered pixel. The type of selection and weighting conditions for each dataset are very important for the quality of the results.

The use of a cross validation allows the evaluation of model restitutions on the French Alps, the Pyrenees, and the Massif Central. The results are very promising when they are compared with the results obtained by other methods (like AURELHY for example). It is undoubtedly the fact of the regional character of the mode of reconstitution.