Climate change modelling projections refer in general to annual and monthly amount of rainfall and potential evapotranspiration (PET). Global change results both from climatic and land practice evolution in response to anthropogenic needs for development and human safety. The presented research study describes a method to detect the respective effect of both sources of change on the flood regimes. The research takes place in the western periurban part of Lyon (France), which is characterized by a rapidly expanding, scattered urban development since the seventies. An increase in frequency of large floods is reported. At the same time a long daily rainfall time series exhibits sensitive changes. In order to assess the respective influence of global change components a diachronic approach is performed with rainfall and land-use data from two decades referred as the seventies (70s) and the nineties (90s). A distributed hydrologic model is calibrated to simulate the effect of the only land use change keeping the same rainfall time series in each period. Statistical comparison tests on observed and simulated flood regimes show a 13% land turn to urban type modifies frequency and severity of small to medium return period floods. The rural component of the periurban area is expected to be more sensitive to the clear enforcement, during the 90s, of the 15 days maximum amount of rainfall. Crossing results it is argued the anthropogenic activity at the observed rate of land use change, in particular urban change, mainly influences the frequent flood distribution. The observed large flood increase results both of longer rainfall events and more heavy daily rainfall. From simulations, a 43% urban cover as planned from 2025 projections would have a very sensitive effect also on larger floods, giving the hand to a more anthropogenic based flood control. Key Words: climate change, simulation model, flood regime

Climate change modelling projections refer in general to annual and monthly amount of rainfall and potential evapotranspiration (PET). Global change results both from climatic and land practice evolution in response to anthropogenic needs for development and human safety. The presented research stud...