(Re)designing urban parks to maximize urban heat island mitigation by natural means

Urban trees play a key role in mitigating urban heat by cooling the local environment. However, the cooling benefit that trees can provide is influenced by differences in species traits and site-specific environmental conditions. Fifteen dominant urban tree species in parks from Mexico City were selected considering physiological traits (i.e., transpiration and stomatal conductance) and aesthetic and morphological characteristics. Species’ physiological performance was measured to explore the potential of trees to reduce urban heat load. Data were collected over a 4-week period in the months of April and May 2020, the warmest and driest months of the year in Mexico City. We used the Thermal UrbaN Environment Energy (TUNEE) balance model to calculate the cooling benefit of each species and the number of individuals necessary to reduce local air temperature. The highest midday transpiration was registered for Liquidambar styraciflua L. (0.0357 g m−2 s−1) and the lowest for Buddleja cordata H.B.K (0.0089 g m−2 s−1), representing an energy consumption and cooling potential of 87.13 and 21.69 J m−2 s−1, respectively. Similarly, the highest stomatal conductance was recorded for L. styraciflua., whereas the lowest was recorded for B. cordata. Based on the species transpiration rates and aesthetic characteristics, we developed a proposal and outline for a 50 X 50 m urban park (i.e., park community) consisting of six species with 19 individuals, and according to the TUNEE model, the proposed arrangement can reduce air temperature up to 5.3 °C. Our results can help urban planners to (re)design urban parks to mitigate urban heat while increasing urban tree diversity in parks.