Signature d'un climat en évolution dans les régimes hydrologiques de la région Rhône-Méditerranée-Corse

Abstract

A river flow regime describes an average seasonal behaviour of flow and reflects climatic and physiographic conditions in a basin. Regularity/irregularity (stability/instability) of the seasonal patterns reflects different dimensionality of the flaw regimes. The changing climate can cause changes in this dimensionality, changing seasonal patterns totally or (adding new seasonal patterns to the variety of those already present in a series making it still more difficult to estimate the seasonal behaviour of flow each individual year. The paper suggests an innovative approach to study a possible signature of climate change on seasonal flow patterns addressing their behaviour in a reduced phase space. The EOF (Empirical Orthogonal Functions) method is used for dimensionality reduction to the first few amplitude functions. The river flow is treated as a non-linear chaotic system with preferred stales. The temporal changes in river flow regimes are studied in terms of the probability density functions of the weight coefficients in the reduced phase space. The approach has been used to investigate the space-time variation of seasonal flow patterns (regimes) of an extensive data set of monthly river flow for the rhone-Mediterrtinean-Corsica region. Two preferred states are identified connected to stable snowmelt-fed and rainfall-fed flow regimes. An attempt is made to follow changes in these states in time.