The Spanish summer known as the San Miguel season is not new, but it is especially topical this year. This time the heat rise was so extreme that the State Meteorological Institute issued a warning about extraordinarily high temperatures for those dates, following an unusually scorching season. Experts point to climate change as a key driver. To shield residents from heat, cities hit by this urban heat island effect must adapt, and one of the strongest strategies is to boost green surfaces. Yet in crowded cities this is far from easy. The path forward is not just to look down at the streets but to also look up and onto the walls.
Vertical gardens have ancient roots, dating back to the 4th century BCE with Babylonia and also appearing in ancient Egypt. Today you can see a living wall on the CaixaForum building in Madrid, where diverse vegetation lives on a single facade. Traditional versions of vertical gardens include flowers on Andalusian terraces and ivy clinging to English cottage walls.
These installations offer environmental benefits such as moderating indoor temperatures in both summer and winter, leading to energy savings, reducing noise and wind impact, and improving outdoor air quality. They also help manage gray water for buildings. A key downside is the high upfront cost of installation and ongoing maintenance.
Reduce mortality rate
To safeguard local well being, the World Health Organization recommends ten to fifteen square meters of green space per person in urban areas. Yet many cities fall short. A Sustainability Observatory study a few years back warned that about nineteen Spanish capitals did not meet this guideline, with serious health consequences. A Lancet report estimated that extreme heat in streets could cause around 6,700 premature deaths, and that roughly one third of these could be prevented by planting trees across thirty percent of urban areas.
According to the data, southern and eastern European cities show the highest heat-related mortality. Several Spanish towns appear on this grim list. For instance, Barcelona has around eight percent tree cover and a heat-related death rate near fourteen percent. Madrid shows rates around nine to twelve percent. Recent scientific studies also indicate that city temperatures rise twice the global average.
The heat island effect pushes urban maxima 1.5 to 10 degrees higher than in rural zones.
That suffocating feeling in city centers during summer and even in spring and autumn is often called the heat island. Thermometers may not drop at night and shelter under shade becomes scarce. Asphalt and concrete absorb heat from vehicles, air conditioning, and sun, transferring it to the air after dawn, keeping temperatures elevated even after midnight. Those tropical nights make sleeping difficult.
Experts explain that the urban air is warmer in these patches because surface color matters. Dark surfaces trap more heat, while vegetation helps keep air closer to ambient temperatures. An architect and professor at the ETSAM-UPM Department of Construction notes, when the day hits 35 degrees, asphalt can reach 50 degrees while vegetation stays near 35 degrees. Buildings also block airflow, trapping heat and creating a distinct city center climate, with maximum temperatures persisting well into the night.
More green and less gray
A push for more greenery and less gray is essential to keep urban populations livable, especially the most vulnerable. Contemporary architecture embraces this shift toward a city model that uses renewable resources, supports recycling and reuse, enables clean and efficient mobility, and expands green spaces. A view from Arquitectura Viva’s article Vertical gardens: the path to sustainability supports this direction.
Vertical gardens can remove up to 85 percent of dust and pollutant particles from the air.
Beyond heavy ground plantings, facade plantings and green walls can soften noise, filter air, and insulate against temperature swings. A quotation from Consuelo Acha, an architect and professor, explains that living walls can also reduce noise by up to 40 decibels, offering a significant acoustic shield and protecting buildings from thermal fluctuations.
There is also potential for dramatic air purification, with up to 85 percent reduction in airborne dust and pollutants. When vertical gardens are installed, a rapid increase in building value follows, thanks to better aesthetics and energy efficiency.
However, experts caution that this is not a one-size-fits-all solution. The high installation and ongoing maintenance costs can be prohibitive. Cheaper options that compromise quality may cause structural issues as weight increases. In some cases, strengthening the structure becomes necessary. It is also important to choose plant species native to the area to ensure survival.
The plant species chosen must be indigenous to the area to ensure their survival.
The Mariposa Hotel in Malaga stands as a regional pride and a European reference for sustainable urban innovation. Its expansive vertical garden spans over 100 square meters and features more than 3,000 plants from 15 species. It not only enhances aesthetics and air quality but also recycles gray water for irrigation in a dedicated system.
Even more renowned is the CaixaForum in Madrid on Paseo del Prado. Designed by botanist Patrick Blanc, it is the first such installation in Spain, featuring more than 15,000 plants across 460 square meters. These vertical spaces demonstrate how cities can be renewed through green design.
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RESEARCH. Antonio Giraldo, geographer and urban planner
These are just one more piece for adaptation to climate change
Antonio Giraldo understands that city planning today centers on the climate change challenge, which drives temperatures higher in large cities during the hottest months.
-Are vertical gardens a good tool to reduce the heat island effect?
-A broader urban model focused on climate adaptation and greening helps, but it cannot stand alone. While these installations can contribute to a cooler, more humid environment, they are not the sole answer to a city’s heat island problem. A comprehensive strategy includes mobility planning, green spaces, public spaces, and urban productivity.
-In what contexts can they be most effective?
-Vertical gardens offer many benefits: beauty, humidity moderation, refreshed air, noise and odor barriers, air cleansing, and biodiversity support. Maximizing these advantages depends on placement and careful maintenance. They work best on solid facades facing treeless streets, and are less suited to motorways where they mainly serve as ornament.
-Are cities speeding up climate adaptation?
-Yes. The concern is that not all cities move at the same pace; some even reverse direction. The reality of worsening climate impacts demands a robust, fair, and accelerated response. Those most at risk will bear the greatest burden, so a solid benchmark for adaptation is essential.
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