“A green area without sufficient trees loses much of its ability to act”

Extreme heat waves are an increasingly intense and long-lasting structural challenge and, faced with some cities turned into asphalt traps With a distinct lack of trees, the “urban climate shelter” concept has gained traction as emergency infrastructure. However, not just any green space acts as a heat shield, since recent research led by the University of Granada evidence that the design, morphology and, above all, the type of trees are critical factors, since a green area without dense coverage loses almost all of its effectiveness in reducing temperature.

Size is not everything. The first results of the ACTERCA project, led by researcher David Hidalgo from the UGR, show the thermal behavior of green areas in the eight Andalusian capitals. To carry it out, they used a combination of satellites, climate modeling, artificial intelligence and thermal cameras, and the research concludes that the cooling capacity depends critically on large trees with dense canopies.

These specific trees are the ones that really manage to reduce the environmental temperature between 3 and 5 ºC compared to areas dominated by impermeable pavements or the classic albero. That is why the key is not to create “green-looking” climate shelters, but to specifically design them to offer good shade and evapotranspiration with the most suitable trees. It is explained as follows by the UGR:

These processes reduce the ambient temperature and significantly improve the thermal comfort of those who use these spaces. On the contrary, green areas with little tree cover lose much of their capacity to buffer heat, which shows that increasing the green area, by itself, does not guarantee effective protection against heat waves.

It’s personalized. The study also highlights that urban design does not admit universal recipes, since in cities like Seville and Malaga, the main problem lies in the albedo and in Córdoba, the threat is building density and soil waterproofing. But if we go to Granada, the geometry of the historic neighborhoods, with narrow streets, offers greater thermal resilience than that of the new urban developments.

Beyond temperature. Although lowering the thermometer is the most visible objective, science warns that the concept of “urban climate refuge” is still in its infancy and its definition lacks consensus. According to a systematic reviewcurrent urban planning is focusing almost exclusively on thermal comfort, leaving the potential of these spaces to promote urban biodiversity or long-term climate mitigation unexplored.

In fact, it is pointed out that climate shelters must be conceived as multi-scalar solutions, since an isolated square is not enough, but an interconnected network is necessary. Along these lines, science proposes specific methodologies (tested in Seville and Malaga) to design shelter networks that classify spaces according to their use: places of temporary relief, areas for daily activity or areas of critical assistance during disasters.

The real challenge. The biggest obstacle facing climate refuges is not thermodynamic, but social. And I know that an excellently air-conditioned park is of no use if those who suffer the most from the heat cannot access it or do not feel integrated.

For example, an analysis at the IERMB on the Barcelona shelter network showed that there are deep intersectional vulnerabilitiessince factors such as economic income, gender and cultural origin determine who actually uses these spaces. This geographical and income inequality is also denounced by Greenpeace Spain, whose reporte warns of a serious lack of protection against heat waves in the most vulnerable sectors of the population, addressing access to thermal comfort as a fundamental right.

We are behind. We know what works and how to implement it, but management is still one step behind. A review at European level which analyzed 97 initiatives in 88 cities revealed a notable institutional disconnection, since national climate adaptation strategies are rarely vertically integrated with local practices.

Plans written on paper take too long to become trees planted on the asphalt. And the message we have on the table is that, to combat the extreme heat of the coming decades, cities do not simply need more square meters painted green on a map, but rather densely treed, intelligently distributed and, above all, socially fair urban ecosystems.

Images | Andy Lee

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