The Heat and Health in Cities (H2C) project to support the prevention of extreme heat in cities

People's exposure to heat during the summer period can have serious repercussions on their health. This exposure is particularly problematic in cities, where it is exacerbated by the urban heat island (UHI), and can be associated with poor air pollution conditions. Today, preventing the risks associated with heat and air quality is a major public health issue in cities. A better understanding of urban-subscale variations in the exposure of inhabitants to heat and air pollutants in summer is necessary to adapt prevention measures and to improve the relevance of weather and air quality forecasts for the assessment of health impacts and for supporting decision-making.

The French research project Heat and Health in Cities (H2C) aims to improve the urban climate services to support heat risk prevention policies, with the Paris region (France) as a case study. In response, the three scientific objectives were identified: (1) Improve our understanding of the impacts of urban covers on UHI, local meteorology and air quality ; (2) Strengthen the synergy between numerical modeling and multi-source observations to assess the variations in population exposure to heat and air pollution, and the associated health risks ; (3) Develop and provide information that is useful for decision-making related to prevention.

Based on the cross-referencing of health, meteorological, socio-economic and urban data (at scale of the region municipalities and Paris' districts), the project has helped to clarify the environmental and social drivers of heat-related health impacts in the Paris region. In addition, an experimental campaign documented the multi-scale variability of meteorological conditions at the surface and in the atmospheric boundary layer. These observations are currently combined with weather and air quality numerical modelling, down to hectometric resolution, to gain a better understanding of the processes involved and the contrasts in exposure in the region and in Paris. The link with thermal comfort conditions in buildings is also explored on the basis of building simulations for a sample of Parisian housing stock. Finally, a major challenge is now the co-construction of territorialized indicators with the help of a group of stakeholders, for the definition of feasible, relevant and understandable urban climate services. For this, a multi-criteria analysis cartographic platform is being developed, fed by knowledge and data from research. The organization of workshops with stakeholders aims to collectively build and test different indicators thanks to a dynamic visual geographic and statistical restitution, and to guide the design of an operational tool.