How much could a carefully planted urban park cool the air?

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Urban trees help mitigate urban heat by cooling their surroundings, but their cooling benefits depend on species traits and local environmental conditions. Researchers selected 15 dominant urban tree species in Mexico City parks, considering physiological traits—transpiration and stomatal conductance—as well as aesthetic and morphological characteristics. They measured the species’ physiological performance to explore their potential to reduce urban heat load.

Data were collected over four weeks in April and May 2020, Mexico City’s warmest and driest months. The researchers used the Thermal UrbaN Environment Energy (TUNEE) balance model to calculate each species’ cooling benefit and the number of individual trees needed to reduce local air temperature.

At midday, Liquidambar styraciflua L. had the highest transpiration rate, 0.0357 g m−2 s−1, while Buddleja cordata H.B.K had the lowest, 0.0089 g m−2 s−1. These corresponded to energy consumption and cooling potentials of 87.13 and 21.69 J m−2 s−1, respectively. L. styraciflua also had the highest stomatal conductance, and B. cordata the lowest.

Using the species’ transpiration rates and aesthetic characteristics, the researchers proposed a 50 × 50 m urban park community with 19 individual trees from six species. According to the TUNEE model, this arrangement could reduce air temperature by up to 5.3 °C. The researchers suggest the results could help urban planners design or redesign parks to mitigate urban heat while increasing tree diversity in parks.