Investigation of urban park cooling efficiency during summer inParis with drones, sondes, and ground measurements

Greening cities is one solution that local authorities are using in order to reduce residents' exposure to heat, which is a major public health issue for urban populations. Urban green spaces, known to be cool spots, are an integral part of local adaptation strategies. For example, Paris' 2024-2030 Climate Plan aims to create 300 ha of additional green space by 2050. Detailed knowledge of green spaces cooling potential and variability factors likely to influence it is needed to plan effective adaptation strategies. This is one of the aims of the PANAME measurement campaign in which an experimental set-up combining in situ surface measurements and vertical profiling of the surface layer using quadcopter drones and soundings has been deployed to measure meteorological variables in five contrasting parisian green spaces and their surrounding built-up areas along summer 2023.

The night-time near-surface cooling capacity of the green spaces relative to their surrounding built-up area has been calculated for different nocturnal vertical turbulent mixing in the urban canopy layer. For nights of low turbulent mixing, often associated with the highest daily temperatures, urban parks cool by several degrees compared with built-up areas, with differences depending on their size and vegetation. A small wooded garden square has a greater cooling capacity than a large grassy esplanade, illustrating the importance of tree cover, even for parks of less than 1 ha, in adapting cities.

For low turbulent mixing nights, the park cooling also often extends vertically over several tens of meters, where a local inversion is found. This stable park layer is not vertically constrained by the buildings surrounding the green space as it can possibly extend higher. It is also only little influenced by the green space size as it is found similarly above urban park of 15ha and garden square of less than 1ha.