Green roofs, an answer for increasingly hot cities

Isabel Aguiar Pinto Mina, researcher from STOL – Science Through Our Lives and from the Department of Biology of the University of Minho (DB-ECUM), reveals that the green coverings on buildings are pointed out as part of the environmental strategy in the fight against the effects of global warming, protection of biomes in urban environments and as a way to mitigate the effects of the predictable heat waves, in which big cities are pointed out as the places most affected by more frequent and intense heat waves.

Green roofs in urban environments are seen as one of the solutions that can alleviate the effect of the predictable heat waves. According to researcher Isabel Aguiar Pinto Mina, the increase in ambient temperature, droughts and extreme weather conditions lead to an increase of the greenhouse effect, with special impact in large urban centres. The STOL researcher states that “the green coverings are seen today as an intelligent and beneficial alternative for the environment, climate change and the way they are felt in big cities, being a very important sector in the environmental and urban strategy of cities in the XXI century”. 

The green coverings have several benefits, both for buildings and inhabitants, as for the environment, highlighting the fact that it has been proven, according to the National Association of Green Coverings (ANCV), that with the use of vegetation on the roofs of buildings it is possible to reduce the temperature in urban centres, acting in the retention of rainwater runoff, improving air quality and urban landscape, being part of the set of arguments that make unquestionable the need for green coverings on buildings in Portuguese cities.

Every year new cities appear that include green roofs as part of their urban planning. A well designed, installed and maintained green roof should extend the life of a building’s roof by at least 2 to 3 times its normal lifespan. In several places in the world, including Portugal, a country where there are functional green roofs that are more than 50 years old and where it was recently (in 2020) launched by the Portuguese Government the environmental fund , which finances the installation of green roofs and vertical gardens. The promiscuous use of Green Roofs in buildings is related, according to ANCV, to political decision, without which there are no significant advances in these matters of urban planning, although it is undeniable its enormous importance and the numerous contributions that can provide towards creating healthy, sustainable, biodiverse and resilient urban territories (in the vision of ANCV).

Green roofs are spread all over the world as examples of “good practices”, because, for José Carlos Costa Valente, in his Dissertation for the degree of Master in Landscape Architecture, entitled “Green Roofs in Portugal – Perception, Attitudes and Aesthetic Preferences Green roofs clearly have the potential to play an important role in mitigating the increase of urban densities, in reducing energy needs, in thermal and acoustic comfort, in protecting ecosystems, improving air quality, managing rainwater, protecting buildings and definitely in aesthetically improving urbanizations. According to this author, it is fundamental in planning a sustainable, promising and, above all, better urban future.

Studies such as Urban heat islands in relation to green land use in European cities published in Science Direct, point out that urban environments will suffer most from global warming, so it is urgent that cities establish new paradigms of environmental sustainability. According to researcher Isabel Aguiar Pinto Mina, the current urbanization of cities may intensify the consequences of global warming. The materials used in the construction of buildings, accessibility and roads, and urban mobility increase the phenomenon of heat islands, affecting especially areas of precarious construction, where high social vulnerability exposes people to constant risks of health consequences generated by excessive heat. The search for a solution focused on environmental sustainability involves this social dimension, demanding from sciences and techniques a transdisciplinary effort for integrated actions that may face the ethical challenge of social inequality among those affected by the harmful effects of climate change.

The expansion of natural or semi-natural areas can mitigate extreme climate effects, based on an idea that is millennia old, for although it is an extremely current technology, the use of green coverings goes back several centuries, both in low and high temperature regions. The oldest and most significant historical references of green coverings are from the period 4000 to 600 BC. 

In Braga, a project integrated in the Municipal Strategy of Adaptation to Climate Change and financially co-funded by the Operational Programme for Sustainability and Efficiency in the Use of Resources (POSEUR) was implemented, covering an area of intervention of about three hectares, where, according to Braga City Hall officials, the aim is the ecological enhancement with the creation of areas of greenery, functional and aesthetic of an area of the city. In Braga, the high temperatures and poor quality are pointed out as worrying in relation to the national context, as such this intervention financed by Community funds, aims to counter the effect of heat island in urban public spaces of the city.

Green roof in Carandá in Braga // Picture Tomás Lourenço

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