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SUMMARYA stochastic mode] for generating hourly hyetographs has been recently developed, in the Cemagref of Aix-en-Provence, to be coupled with a rainfall runoff conversion modelling. Thus, by simulation of very long periods (1000 years for example), we obtain a large number of hourly hyetographs and flood scénarios that are statistically studied and used in flood predetermination problems. The rainfall model studied is based on the theory that rainfall can be linked to a random and intermittent process whose évolution is described by stochastic laws. It is also based on the hypothesis of independence between variables describing hyetographs and on the hypothesis of the stationary nature of the phenomenon studied. Generating a rainfall time séries involves two steps: descriptive study of the phenomenon (nine independent variables are chosen to describe the phenomenon and thèse variables are deflned by a theoretical law of probability fltted to the observations) and création of a rainfall time séries using descriptive variables generated randomly from their law of probability. Initially developed on the Real Collobrier watershed data, the model has been applied to fifty raingauges located on the Mediterranean French seaboard. The extension of the model applying area has shown heterogeneousness in the results. Therefore, modifications hâve been made to the model to improve its performances. Among thèse modifications, three of them hâve presented notable improvements.A study of the sensitivity of the parameters has been made. Parameters of shape variables and of some other variables had only a slight influence on depth of generated rainfalls. But, the law of mean rainfall intensities clearly differentiates the stations. Then, a theoretical probability distribution for the storm intensity variable, less sensitive to the sampling problems, has been Finally, the modelling of storm persistence in a same rainfall épisode has been studied to generate some high 24 hours maximum rainfalls. Persistence modelling is entirely justified by the fact that "ordinary storms" cluster together around the "main storm" (the "main storm" is the greatest storm of an épisode and the "ordinary storms" are the other storms of the épisode). When the study of this phenomenon is extended, it can be observed that there is a certain positive dependency between occurrence probability of the "main storm" and occurrence probability of storms which corne before or after it. Two combined effects occur: within one rainy épisode, the strongest "ordinary storms" are preferentially clustered together around the "main storm", and considering the number of "ordinary storms" throughout ail the épisodes, the strongest storms close to the "main storm" are preferentially associated with the strongest "main ...