The increasingly intense and frequent heat waves make our cities real “heat islands“. But trees can actually help us combat extreme heat? A new international study published in Nature investigates the effectiveness of urban greenery in mitigating temperaturesoffering concrete solutions for a fresher and more sustainable future.
Cities, with their asphalt, concrete and heavy traffic, are particularly vulnerable to heat waves. The “urban heat island” effect intensifies temperatures, putting citizens’ health at risk and increasing energy consumption for cooling buildings. In this context, trees present themselves as a natural and effective solution to mitigate the heat and improve the quality of urban life.
But planting trees may not be enough. In the study they were analyzed over 180 studies on the topic, conducted in 110 cities around the worldto understand how to maximize the benefits of urban greenery. From the data collected it emerged that the introduction of trees it reduces peak monthly temperatures below 26 degrees in 83% of the cities studiedreaching the ‘thermal comfort threshold’. However, cooling capacity varies significantly around the world.
The results show that the effectiveness of trees in reducing temperatures depends on a combination of factors: the characteristics of the trees themselves (species, crown shape, type of leaves), urban morphology (building density, street orientation) and the climate. Trees cool the urban environment through several mechanisms, including shading, transpiration and modification of air flow. The treetops block solar radiation, reducing the heat absorbed by the surfaces; the leaves release water vapor, which cools the surrounding air; and the presence of trees modifies the air flow, promoting ventilation.
The study showed that trees can reduce temperatures perceived by pedestrians by up to 12°C, with a greater effect during the hottest hours of the day. But the effectiveness varies depending on the climate. In the typical tropical savannah climate, trees can cool cities by up to 12°C, as recorded in Nigeria. However, in this same climate trees warm cities more at night, by up to 0.8°C. Trees do well in arid climates, lowering daytime temperatures by just over 9°C and warming nighttime temperatures by 0.4°C. In tropical rainforest climates, where humidity is higher, the daytime cooling effect is about 2 degrees, while the nighttime warming effect is 0.8°C. In temperate climates, trees can cool cities by as much as 6°C and warm them by 1.5°C.
The study examined research conducted in various Italian cities, including Rome, Lecce and Catania. Italy is among the countries with the highest number of studies, demonstrating the growing interest in urban greenery on the Peninsula. The results show that in Italian cities, characterized by a temperate climate, trees can contribute to significantly reducing temperatures, especially if planted strategically, considering the species, location and density.
The study offers valuable indications for planning urban greenery, such as choosing the right species based on the climate and urban morphology, planting trees in the right place to maximize shading and ventilation, and the integration of trees with other solutions such as green roofs and vegetal walls.
Planting trees in the city is not just an aesthetic issue, but a fundamental strategy to manage the effects of climate changeor, improve air quality, reduce noise pollution and promote biodiversity. Investing in urban greenery is an investment in the future of our cities. Trees, in addition to mitigating the heat, offer numerous benefits for the health and well-being of citizens, making urban environments more livable and sustainable.
