Prévision spatiale des hauteurs de précipitations journalières

A Spatial forecast of daily precipitation heights

EDF/DTG, Grenoble

Abstract

A numerical forecasting method has been devised and improved on over more than ten years. It allows daily rainfall height in a 24 h interval to be forecast covering 33 catchment basins of approximately 1000 km2, located in mountainous regions of France. A 30 year historical file has been established for daily levels (at 0 h) of areas at 1000 and 700 mbar over the West of Europe and refined by an analysis of the main parameters associated with daily rainfall observed over six mountainous regions in France. The most analogous meteorological conditions within a circle of small radius, whose centre and size vary every day, are selected in operation at 6.30 a.m. on the basis of the atmospheric conditions observed at 0 h and forecast 24 and 48 h ahead by the Department of Meteorology using inter-computer telephone links. The calculation of the multiple regression equations associated with the analogous conditions for each of the six regions, and the distorsion of the area at 1000 mbar within 24 h, allows a probability forecast to be made of rainfall height for the day and the morrow for 33 pilot basins. The results obtained using this dynamic method over two recent years are compared with the results obtained for each working day from forecasts made by applying fixed regression equations run earlier from the historical me as a whole transmitted from Paris to Grenoble between, on the one hand, daily rainfall and, on the other, atmospheric conditions at 0 h (700-1000 mbar) and distortion within 24 h.