Quantifying the Influence of Parks on Urban Heat Island Through Assessment of the Cooling Effect in five U.S. cities

Urban expansion and intensification, represented by an increase in residential, commercial, and industrial land uses, have continuously invaded the blue-green landscapes in cities. The induced urban heat island (UHI) effect poses a major risk to public health under global warming. Parks, the common and major component of green infrastructures in cities, are found to exert a cooling effect in the areas themselves and their surroundings and may provide an opportunity to alleviate urban heat stress. However, it is still a challenge for urban planning to optimize park design for heat adaptation, as the park cooling effect has not been robustly quantified and mediating influences are still being understood. In this work, we use remotely sensed thermal satellite imagery and a Gaussian model to extract the cooling effect features of 384 parks in five U.S. cities. Results show that most parks serve as a local cooling island and most of the cooling effect only exists within a distance of 100-200 m from parks boundary. Furthermore, we propose an index park cooling efficiency (PCE) to quantify the degree to which a park can cool an equivalent surrounding area outside the park. The average of PCE in five cities is between 1.03-2.35 and is associated with a range of factors. Park geometry (area, perimeter, and shape) shows high importance and positively correlated impact on the PCE. Park irrigation can significantly improve the PCE in Los Angeles and Austin, while it is less efficient in the other three cities. The results of this study deliver better understanding to support design of green spaces with effective cooling capacity to mitigate the UHI in cities.