Assessing impact of global change on flood regimes

Global change results both from climatic and land practice evolution in response to anthropogenic needs for development and human safety. The purpose of this paper is to describe a method to assess 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 1970s. An increase in frequency of large floods is reported. At the same time, a long daily rainfall time series exhibits sensitive changes in rainfall durations and intensities. Independent analysis of global change components is performed using observed rainfall and land‐use data from two disconnected decades. A marked difference in natural climatic regime variability between decades is used as a surrogate to study effect of climate change.

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 percent urban cover as planned from 2025 projection would have a very sensitive effect also on larger floods, giving the hand to a more anthropogenic‐based flood control.

Despite an expected increase in rainfall and flow variability regimes as a result of climate change and a projected growing of the world urban population, there is a lack of methodology to address combination of both processes on the flood regimes. A method is proposed to judge on the respective importance and interplay of these processes.