Adapting cities to climate Change : a systemic modelling approach

To answer the climate change challenge, all states have to reduce their greenhouse gas emissions, but also to adopt adaptation measures to limit the negative impacts of global warming on the population, the economy and the environment. The question arises especially for cities. Because of complex interactions between climate change, the evolution of cities and its inhabitants, studying adaptation strategies for cities requires a strong interdisciplinary approach: urban planners, architects, meteorologists, building engineers, economists, social sciences. Our four-step methodology consists firstly of defining interdisciplinary scenarios at several scales influencing the city evolution; secondly of simulating long term city evolution based on socio-economic and land-use models; thirdly of calculating impacts with physical models, and finally of calculating the indicators quantifying the adaptation strategies. Interdisciplinary systemic modelling performs well to evaluate several adaptation strategies for a very broad range of topics. Some of the results obtained for the agglomeration of Paris through our interdisciplinary research projects VURCA and MUSCADE will be discussed: A finding is that Urban planning strategies may have unexpected influence on city expansion when considered on the very long term of the climate change. Another is that the combine effect of global warming and UHI can lead in the future to larger energy consumption in summer than in winter. Indeed, air-conditioning will probably be necessary in 2100, because of expected stronger, and longer, heat waves. Limiting the UHI intensity allows for energy savings, and hence contributes to climate change mitigation. Adaptation strategies exist to limit air-conditioning use, both in time and intensity. Analysis of several vegetation strategies, at several spatial and planning scales (from agricultural practices in the city surroundings to urban trees and green-roofs) have been performed and evaluated. Architectural choices also allow to reduce the UHI. Finally, inhabitants' use and practices seem to be an efficient lever to reduce energy consumption in buildings and its impact on the urban climate.