Comparison of the Impact of Three Climate Adaptation Strategies on Summer Thermal Comfort – Cases Study in Lyon, France

Nowadays, the study of the outside thermal comfort is more and more taking into consideration in the urban design process. In a climate change context, town planners have to find solutions to mitigate the effects of the global warming and to ensure that outside spaces designed in new districts will remain liveable.

In the framework of the EVA project, simulations were carried out to compare the effect of three urban cooling strategies on the thermal comfort in summer. Various urban greenery types, water aspersion systems and cooling materials are applied to three districts in Lyon, France. A set of simulations was designed to explore different configurations:

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  cooling strategies were first applied one by one in each district,

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  a composition of the three strategies is considered in a second step to optimize their effect,

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  cumulative effect is finally investigated by deducing one of the components from the optimized configuration.

Simulations were performed using Solene-microclimat which realizes the full coupling between a CFD code and a thermo-radiative model. In this way, Solene-microclimat enables to calculate and evaluate the evolution on the urban microclimate at a district scale considering physical parameters in a completely discretized way. Modules have been introduced in this model to represent different kinds of adaptation strategies such as vegetation (green roofs and walls, trees, lawns) and water aspersion. For each case, the daily variations of surface and air temperatures fields are obtained and compared. The resulting mean radiant temperature is evaluated and investigated for the studied space of each district. Finally, the thermal comfort is assessed using the UTCI index. Findings indicate that vegetation, in particular when including trees is the more efficient, due to its shading effect. Even if water aspersion can strongly lower the surface temperatures, its effect on thermal comfort is local and limited compared to the effect of vegetation. Due to reflection effects, high albedo materials are less efficient concerning external thermal comfort.