How small green spaces cool urban neighbourhoods: Optimising distribution, size and shape

How can green spaces smaller than 1 ha improve outdoor thermal conditions in urban neighbourhoods? Considering the variability of cooling effects based on the relevant urban design parameters of size, shape, and spatial distribution, this study entailed development of different design scenarios combining these parameters for four neighbourhood typologies and simulates the thermal sensation of these scenarios using ENVI-met. Three aspects of cooling effects — the inside and outside cooling as well as the Park Cool Island (PCI) effects of the green spaces are separately analysed. The study shows that inside the small green spaces, the mean Physiological Equivalent Temperature (PET) of different cases can vary up to 4 ℃. Larger green spaces with a squared shape lead to cooler PET inside. For a good cooling outside the green spaces, a configuration of grouped small green areas can reduce the PET by 1.3 ℃, with distribution of the green spaces being the most influential factor. The PCI effect is mainly determined by size and shape of the green spaces, where a bigger size and squared shape leads to better cooling effects. But for neighbourhoods with radial streets, it is more related to the spatial distribution, which can result in a reduction of 10.2 ℃ in PCI for linear green spaces next to narrow streets. Guidelines for effective design scenarios are generated from this research, providing urban designers and planners with practical reference in neighbourhood greening projects for cooler cities.