Spring is here, with summer temperatures. The heat has been felt since the end of March and is only expected to intensify over the coming months. Memories linger of last summer, which the Copernicus Climate Change Service says was the hottest ever in Europe. We don’t yet know what this summer will be like, but what we do know is that the planet is heating up and these extreme and out-of-season phenomena are becoming increasingly common in cities around the world. Lisbon, with its Mediterranean climate and increasingly high temperatures, is no exception. But what if there were places in the city where we could take shelter from the heat – “climate refuges”?
“A climate refuge is a place where people can go during heat waves. They can have trees or bushes to create shade and can have water features that allow people to cool off,” says data analyst Manuel Banza. This young resident of Lisbon believes these refuges could be a good way to mitigate the urban effects of climate change. This encouraged him to survey the condition of these refuges in Lisbon, where temperatures have already exceeded 30°C and concerns grow over the lack of options for getting some relief from the heat during the day.
In April he published an article, “Identificação e Priorização de Locais para Refúgios Climáticos em Lisboa” (“Identification and Prioritisation of Locations for Climate Refuges in Lisbon”), in which he named the specific locations most in need of such shelters at a time when heatwaves are becoming increasingly frequent and precipitation more irregular. The work was inspired, on the one hand, by a proposal from the political party Livre, which was approved by the Lisbon Assembly in July 2022, calling for the establishment of a network of climate refuges in the city to be identified that same year – which ultimately did not happen, but we'll get to that. It was also inspired by efforts in the Catalan capital Barcelona, which is at the forefront of this process, and which has established a network of climate refuges in schools, courtyards and libraries.
To identify the places most in need of climate refuges in the city, Manuel Banza began by visualising the heat island effect at dusk. This phenomenon refers to the increase in temperature in urban areas, where heat is felt more intensely in comparison with the surrounding rural areas (in the case of Lisbon, the airport weather station is used as the reference, due to the sparsity of buildings in the area). He then analysed the spatial distribution of green spaces and water features across the city, checking the relationship with the areas of greatest sun exposure and solar incidence.
Identifying the location of points of interest, such as municipal libraries and swimming pools, drinking fountains, green spaces, ponds and fountains recorded on an interactive map, and important features in climate refuges, he used criteria such as proximity to gardens, parks and libraries, the distribution of trees and number of inhabitants per block (BGRI, according to Census 2021 data) to identify the most critical areas of the city in relation to mitigating the heat effects caused by climate change. After analysing these factors, he was able to identify the six zones that are most exposed to the sun and which urgently need refuges: Ajuda, Alto de São João – Morais Soares, Chelas, Bairro do Rego, Baixa and Parque das Nações. The conclusion for the latter two is consistent with the results of studies that have been conducted by the University of Lisbon (UL) over the last 40 years. According to Cláudia Reis, a researcher from the UL's Climate Change and Environmental Systems research group (ZEPHYRUS), the waterfront is always hotter, even with the influence of the wind and proximity to water.
It is known that due to urban morphology and anthropic heat - which refers to the temperature increase caused by human activities, such as vehicle traffic, construction of buildings with dark-coloured materials that absorb heat, soil heating, urban density and lack of green areas, such as parks and trees - cities tend to heat up more than rural areas with vegetation. In Lisbon, the temperature differences caused by the heat island effect can range from 2°C-3°C. However, in some places the difference can be even more significant, with a variation of up to 11°C compared to the values recorded at the airport, says António Lopes, associate professor at the university’s Geography and Regional Development Institute (IGOT), researcher at the Geographical Studies Centre and director of ZEPHYRUS.
Despite its many parks, trees and shaded areas, the Parque das Nações is one of the districts in Lisbon worst affected by the urban heat island effect. This is due to the construction carried out in that area, which distorted the original plans for Expo 98 and did not take into account the environmental impact of all those buildings on air circulation, as was proved by the Lisbon 2020 Heatwaves project that forms part of the City Council’s Climate Action Plan, in which António Lopes and Cláudia Reis participated. “Expo was planned to allow the wind to enter the city. A very hot summer was expected, and so all the buildings were designed to allow the breeze to enter, but then in the following years they started building very tall buildings that began to block the wind,” António Lopes says. The Metropolitan Climate Change Adaptation Plan, to which the researcher also contributed, predicts this situation will get worse due to the hot air coming from North Africa and the interior of the Iberian Peninsula.
The problem is different in the Baixa. In his work, Manuel Banza points to factors such as the concentration of people (tourists in particular), tall buildings and lots of asphalt-covered streets as factors that contribute to the retention of heat. Additionally, here there are no open spaces or green areas that can absorb the heat. António Lopes explains that vegetation is very important in promoting evapotranspiration, the process by which leaves transpire and extract energy and heat from the environment.
Cooling down: breezes and shade
Contrary to expectations, not even night helps. In dense urban areas with compact buildings and poorly ventilated streets, cooling during nocturnal hours does not occur and instead the energy is stored, resulting in warmer urban areas. This is what happens on the waterfront, along the eastern part of the city and in the Baixa. In other words, the places most affected by the absence of wind are those where breezes are presumed to penetrate, but which are blocked by buildings.
Cláudia Reis has been using wind modelling to study the effect of the breeze on the city. The most important breezes come from the west, from the Tagus and the Atlantic Ocean, and occur “normally on about 30% of summer days,” managing to cool the most critical areas of Lisbon by up to 4 degrees. However, this breeze does not reach the whole city. The construction of buildings – in the city that is growing towards the north – blocks
“the northerly winds [which come from the northeast] that are very important for cooling down the city centre and removing pollutants.”
Among a set of effective measures in the fight against climate change, Cláudia Reis highlights the replacement of impermeable surfaces by permeable ones as a viable option, since these surfaces retain water and do not absorb as much heat. The reduction of traffic in some of the city’s streets is another suggested measure, since the pollution produced by vehicles aggravates the heat island effect and contributes towards the retention of this “bubble” of heat in the city. As she noted at a conference on urban climate in Vienna, installing showers could also be an option for mitigating the urban heat effect.
Another measure that is as simple as it is effective is the creation of shade. In addition to mitigating the heat effect, it provides relief on hot, sunny days, and also reduces the need for the excessive use of air conditioning. However, she accepts not everyone has access to this equipment. Especially when they are at home and have no alternative way to cope with high temperatures. “At night, the most vulnerable population – children and the elderly – can be affected by the lack of any options that can help them cool down, as many do not have access to air conditioning at home or cannot go to cooler spaces, such as shopping centres,” she emphasises with concern.
As for the selection of trees to plant in Lisbon, deciduous species are recommended, since they block solar radiation during the summer and allow it through in the winter. Where it is not possible to plant trees in critical areas, it is possible to install removable awnings after the summer, she adds. However, as António Lopes stresses: “we need to green the city.” Vegetation and the areas of green in the streets of Lisbon play a crucial role in the urban cooling process.
Islands of cool in the heart of the city
A study by Cláudia Reis confirmed two city parks – the Gulbenkian Gardens on Avenida de Berna and the Fernando Pessa Gardens on Avenida de Roma – had an impact on the temperature of the surrounding streets. Using the IGOT meteorological station as a reference, temperature measurement devices were installed at several points around the Gulbenkian Gardens and in areas outside, including on Avenida Miguel Bombarda. The study revealed that 50 square metres of vegetation cover is required to reduce the air temperature by 1 degree, although this reduction is limited to a specific area.
“At the Gulbenkian, I was able to identify temperature reductions extending up to 100-150 metres – as far as Avenida Miguel Bombarda Avenue. This means the influence of that space, which covers about three to four hectares, could be felt in the surrounding streets.”
The same cannot be said about other green spaces, such as Parque Eduardo VII and Fernando Pessa Gardens. Observation of the latter showed grass has practically no cooling effect: in fact, quite the opposite. "We observed that often the park was in fact hotter than the street.” And why is that? “Because most of it is grass,” which absorbs more energy than vegetation.
“I often use the Gulbenkian Gardens as a climate refuge. It’s a very good example of how a green space in the city centre can have a significant impact on reducing the ambient temperature,” says Manuel Banza, while pointing to the map on which the heat island effect is visualised at dusk. “As you can see, the garden is blue, which shows the temperature is below the reference line. In addition to mitigating heatwaves, these green spaces can be cooler than normal.”
Torel Gardens on Rua Júlio Andrade is another example of a good climate refuge. However, Manuel adds it is essential to consider the composition of these green spaces, including the presence of shade and water elements, both of which are crucial for creating a true refuge. Alameda D. Afonso Henriques “can never be a refuge,” he says. “To be one there must be shade and water elements.” The presence of green spaces in the city with a range of vegetation and trees, such as the Gulbenkian Gardens, has a positive effect on thermal comfort in the respective areas. These are the so-called islands of cool. The analyst says it is also important to consider planting trees along the streets, while noting that there are no trees on the street where he lives. The temperature difference between Rua Pascoal de Melo and Avenida Almirante Reis, which are at right angles to one another, can reach “4 or 5 degrees” because of the lack of trees along the latter.
Climate refuges as social spaces
“With the increased frequency of extreme temperatures, it is crucial that cities prepare to mitigate this problem,” warns Manuel Banza, emphasising that Lisbon faces a lack of public spaces for socialising and leisure that are not in places with heavy traffic or where there are pedestrianised streets or streets with trees. The creation of refuges like this can help solve the problem of heat islands and high temperatures, while also improving the public space by enabling people to enjoy the city rather than just using it as a “means of getting from point A to point B.”
In other words, the idea of climate refuges also involves creating spaces for socialising that can “promote a sense of belonging in that neighbourhood and parish.” Building housing without including green and leisure areas is not a viable solution, he says. Areas such as Chelas and Bairro do Rego, which he considers to be “historically forgotten,” were built without any consideration for the importance of areas to socialise, which has resulted in the creation of “huge buildings” with hardly any green zones and limited public spaces. This causes “a negative impact on both public health and the economy.” he adds.
Manuel proposes involving the community in identifying these spaces through a “bottom-up process of co-creation and ethnographic research.” This will ensure the solutions are both appropriate and accepted by the community, promoting a sense of shared ownership by the residents and users of the location. The aim is to encourage the independence of the population and their commitment to the space.
The presence of green space is also crucial for the absorption of water during floods. This is an example of the nature-based solutions concept, a set of actions and policies that use the power of nature to address urgent social challenges, such as threats to water security, the increasing risk of natural disasters and climate change. These solutions involve the sustainable protection, restoration and management of ecosystems, while at the same time preserving biodiversity and improving human well-being.
Manuel adds that fitting awnings to windows, for example, would help reduce the direct impact of the sun and increase thermal comfort in homes, especially in areas such as Arroios, where extreme temperatures are felt intensely regardless of the weather. However, refuges should not only be thought of as a means to mitigate heatwaves. Climate change also enhances phenomena related to the cold. With that being so, António Lopes says these refuges must also take this into account, and offer a refuge for those who struggle to maintain a comfortable temperature.
The heat is on and Lisbon responds
According to the study “Excess Heat Factor climatology, trends, and exposure across European Functional Urban Areas”, published in 2022 in the scientific journal Weather and Climate Extremes, Lisbon is the seventh-most exposed European city to heat waves, also taking into account the elderly population. 2022 was the hottest year in mainland Portugal since 1931, with the annual bulletin of the Portuguese Institute for Sea and Atmosphere recording six heatwaves. Given these data, how is Lisbon preparing to face this coming summer?
The refuges can be created in places that are well insulated, says António Lopes. “As long as you can control the relative humidity, and it’s not too high, you can use any space.” While still being assessed, it has been suggested the interior of churches is one of the best options.
This was precisely one of the recommendations of the proposal presented by Livre in July 2022, which called for the immediate creation of a network of climate refuges as a response to that summer’s heatwaves. “The proposal we drew up last year had two parts: one was to immediately identify a structure for this year; and the other was a network of climate refuges for the summer of 2023, but nothing was done about that,” says Livre city councillor Isabel Mendes Lopes. “It was just a matter of using existing spaces, such as libraries, churches and museums. Ensure the city is covered with places where people can protect themselves from high temperatures, guarantee they are accessible and that they are within a 10-minute walk,” she adds.
The party’s recommendations were not immediately implemented. However, according to the latest report, “Written Information from the Mayor”, Lisbon City Council's Environment, Energy and Climate Change Department is currently working on a “Climate Refuge Network”. The project is still in the research phase, collating information on similar initiatives that have been implemented in Paris, Barcelona and some US cities. There is also a “Cooling the City” programme that seeks to combat the effects of heat on the population and which envisages the transformation of urban squares into greener and cooler spaces while also increasing the number of tree-lined streets.
There are also international guidelines that recommend maintaining the proportions between the width of a building and the width of a street, since it is known that high-density built-up areas can reduce the wind speed, absorb solar radiation and increase the local temperature. “Lisbon City Council needs to adapt these guidelines and incorporate them into its municipal regulations,” says António Lopes.
“We have a triple problem in the cities: the heat island effect, the consequences of climate change and heatwaves. Climate change is a reality that has been going on for years while projections for the future indicate temperatures may double, perhaps more,” he warns. “There are three ways we can deal with climate change: mitigate, adapt or suffer.” What we must do right now, especially along the city’s waterfront, is to act at the city block level.
Cláudia Reis stresses the urgent need to find solutions that will deal with the extreme temperatures forecast for Lisbon. In her study into thermal comfort in Lisbon, in which she modelled several areas in different neighbourhoods, she noticed that in terms of perceived temperature, in a few decades the mercury could reach 50°C-55°C during the day.
“What we are experiencing now is just the tip of the iceberg: Lisbon will become completely unbearable in the summer.”
Barcelona, a benchmark
Climate change has had a significant impact all over the world, including the increase in the frequency and intensity of heatwaves. Faced with this challenge, many cities have sought to develop solutions to protect their citizens from the excessive heat, especially among more vulnerable groups. Barcelona has been at the forefront of this process.
Since 2019, climate refuges in the Catalan capital have provided relief to the city’s residents during heatwaves. More than 200 of these refuges have been established in schools, community centres and other public buildings located all over the city. The priority is for everyone to be within ten minutes of one of these refuges and for them to be easily identified. To this end an interactive online map is available to show people where the closest one is in the event of urgent need.
Fitted with air conditioning and provided with drinking water, these shelters are designed to accommodate a large number of people. The opening of the Gabriel García Márquez Library last June, during one of the hottest summers since 1914, demonstrates that libraries designed as climate shelters are already a reality: comfortable, spacious with diverse vegetation and co-working spaces.
But thermal comfort does not end there. Streets are also a reflection of cities preparing for the challenges posed by climate change. They are greener and safer spaces, increasingly safeguarded for the entire population, reducing the space for the car.