City-scale assessment of outdoor heat shelter availability under climate change conditions: a simulation-based methodology

The paper proposes a new methodology for assessing the availability of outdoor heat shelters in cities during future hot summer days. Heat shelters are identified on 1 meter resolution physiological equivalent temperature (PET) fields obtained with SOLWEIG simulations. Input weather data are representative hot summer days (RHSDs) which are processed from an analysis of future weather projections, for three stages of climate change evolution. The heat shelter availability is assessed through three indicators: the heat sheltering status, the heat shelter area per capita, and the heat sheltering performance. In this way, the methodology makes it possible to assess the time evolution of the heat shelters availability, over the course of the day and over the century, in large urban areas, for different levels of protection against heat. The methodology is applied to the city of Lyon. In this city, heat shelters will not provide thermal comfort; they will at most protect against heat stress exposure. During the core of the day, at the end of the century, heat shelters are exclusively located in shaded areas with sufficient ventilation and low exposure to reflected solar radiation. Locations under large patches of continuous tree cover or at the foot of building façades without overlooks fulfill these conditions. In the parks, the daytime average heat shelter area is proportional to the surface of the tree canopy.