A French national project
was set up in 2002 in order to study the variation of floods and droughts in
France, based on a large set of discharge data series. Numerous approaches can
be used to study trends and variations on hydrological data series, e.g.
statistical tests, segmentation procedures, Bayesian approaches, and
multivariate or regional models. A comparative analysis aimed at defining a
general framework for the selection of a limited number of tests, based on the
statistical properties of the hydrological data series (sample size,
autocorrelation) and the prior knowledge of the type of distribution and the
expected change. The first results on a set of about 200 French long data
series do not show conclusive proof that climatic change has affected flood and
drought regimes. A Bayesian model has finally been developed to incorporate
hydrological nonstationarity into frequency analysis, using MCMC algorithms for
the weighting of different time dependent models.