Modeling methods to assess urban fluxes and heat island mitigation measures from street to city scale

The urban microclimate is due to complex physical interactions with the contribution of water balance, thermo-radiative exchanges and airflows. In this paper, we present and discuss modeling of heat island effects and mitigation techniques in order to give consistent results considering different time and space scales, and different fluxes (heat, water and winds) from ground to urban canopy, including buildings. The models and numerical descriptions are presented in detail and illustrated on typical examples of heat island mitigation techniques. At the neighborhood scale, alternative rainwater management techniques are studied by considering their impact on both seasonal water table depth and surface-atmosphere heat fluxes. Assessing the building thermal performance interactions with the microclimate requires adapted models that have to be refined for a better description of building envelope and systems effects. Two examples at the street and the neighborhood scale, modifying the building radiative properties or using green envelopes, show how simulation brings out the potential benefits of these techniques for the heat island mitigation and building energy performance.