Quantification and mapping cooling effect and its accessibility of urban parks in an extreme heat event in a megacity

With the rapid process of urbanization and global warming, extreme heat events occur frequently, endangering urban dwellers' health. Urban parks could alleviate the severe urban heating climate. However, due to the scarcity of urban land, it is impractical to plan and design urban parks by increasing the blue-green space without restriction. Few studies have focused on optimization and the equity of the parks' cooling service. This study quantifies four cooling indicators of urban parks in Wuhan city, park's cooling intensity (PCI), park's cooling area (PCA), park's cooling gradient (PCG), and park's cooling efficiency (PCE), analyze the drivers for four indicators, discuss different cooling bundles (urban parks with similar specific cooling ability are grouped into bundles) for the specific heat mitigation demands, and map the spatial accessibility for residents to parks' PCA using spatial network analysis. We find that 54 of 60 urban parks have significant cooling effect, with average PCI of 3.5 ± 0.2 °C, PCA of 131.6 ± 29.6 ha, PCG of 17.9 ± 1.5 °C/km, PCE of 4.5 ± 0.8. Blue and green infrastructure inside parks and impervious surface ratio surrounding the parks play significant roles in cooling service. Larger urban parks usually have larger PCA, but lower PCG and PCE. Five cooling bundles clustered with specific dominant cooling indicators could be references for the specific demand considering tradeoffs in urban parks' design and planning. Taking one step further, we unmask the unequal accessibility of the urban parks cooling service in one extreme heat day: 83.6% of the residents in the central area can enjoy the urban parks' cooling service within 30-min walk, while most residents (74.4%) in suburbs are not able to access to the cooling service within 30-min walk. Our study should be valuable for the urban planning and practice to find heat mitigation solutions and improve residents' heat comfort, also helpful for local municipalities to consider the urban parks' service provision for marginal groups.