Inventing cool in the heatwave

12 July 2021

“This year, we’re already about to get hit with the third heatwave of the summer,” says Barsi Orsolya, Deputy Head of the Department for Environment and Climate at the city of Budapest. A 2020 report by the Joint Research Centre (JRC), the European Commission’s science and knowledge service, has found that “with unmitigated climate change, a current 50-year heatwave may occur almost every year in southern Europe, whereas in other regions of Europe such events may happen every 3 to 5 years.”

An increase that isn’t without consequences: mortality due to extreme high temperatures is estimated to increase significantly from the current 2,750 fatalities a year. Depending on the scenario, the EU population could see between 30,000 and 96,000 deaths a year due to climate change-induced heatwaves. “With nearly three-quarters of the European population living in an urban environment and the fact that temperatures can be more than 5 degrees higher in cities compared to the surrounding rural areas, it will be crucial to reshape our cities to minimise the urban heat island effect,” states the JRC report.

Budapest and Barcelona, among other cities such as Vienna, are testing simple solutions to minimise the urban heat island effect, and they hope to convert them into permanent solutions for their city strategy.

Mission: ‘Fresh public spaces’

“Last year, we started the testing phase for the ‘cooling islands’,” says Barsi, “and we focused on creating more shade in frequently used public spaces.” Budapest’s ‘cooling islands’ consist of colourful temporary shelters offering shade, plants, and benches to sit on and rest. The pavement under and around the shelters has also been painted white to reduce heat absorption. They are set up mainly around the bus stops in the city centre as they are exposed to the sun from sunrise to sunset.

Cooling shelter structure in Budapest

“These structures are usually used for setting up the speakers and lights at concerts and festivals,” says Barsi. “But last year, because of Covid, we had no such events, so the companies were thrilled to provide us with the structures for a different purpose, and people like them.”

Her department hopes to offer this as a permanent solution in the future, but it all depends on their budget constraints. In the meantime, Barsi says they hope to inspire the transport company and the different districts to think about the heat island effect and integrate cooling solutions when starting new construction sites.

In Barcelona, people can access a network of indoor and outdoor ‘climate shelters’. These vary from libraries, parks, neighbourhood centres and other public spaces that are kept open and made comfortable for vulnerable people, such as elderly people or children, to offer thermal comfort in addition to their usual services. By the end of this year, the city will have a network of more than 160 climate shelters, doubling the previous year’s offer. This means that almost 90% of Barcelona’s population will be able to reach a climate shelter in less than ten minutes by foot.

Another strategy to keep the urban environment cool is hosing the pavement. In Budapest, the cleaning trucks punch in extra hours in the morning and evening during heatwaves to keep the streets wet. “We compared the map of the usual routes of the cleaning vehicles with the heat map of the city,” explains Barsi. “So we could see where the heat island effect was stronger and base the vehicles’ routes on that data.” The service can also be booked by other public and private actors when needed.

Pick your shaded path

Barcelona is also basing some important decisions on relevant data. The city first studied how the different districts were affected by heatwaves and which are more vulnerable. The study found that neighbourhoods with a higher concentration of population aged 75 and over, with buildings with poor energy performance and the lack of vegetation were more vulnerable to heatwaves and therefore needed more support. The study recommended solutions like increasing green spaces and improving the thermal comfort of buildings, especially in these most vulnerable neighbourhoods.

The team in Barcelona also had fun with the data at their disposal to propose ‘fresh’ paths in the city. The ‘Cool Walks App’ was born in 2019, in the framework of a data visualisation contest and aimed to promote the use of open data, from the minds of the Geographic Information System (GIS) team in Barcelona Regional.

Using the Light Detection and Ranging (Lidar) technology, a high-resolution sensor that shoots laser beams towards the surface and interprets the return of the pulses, the team in Barcelona can map the surroundings of an area. “For example, if the beam hits trees, it returns multiplied because it can have a partial return on a leaf or a branch until it hits the ground,” explains Albert Carbonell, Biologist and Analyst with the GIS team at Barcelona Regional.

The team decided to concentrate their efforts within the Barceloneta neighbourhood on the coastline, a mostly pedestrian area with touristic interest. With the information from the Lidar and additional tools and datasets to refine their mapping, the team built three journey options for the ‘Cool Walks App’. People can choose the most direct route, a longer path with more shade, or the ‘vampire mode’, which avoids all direct sunlight.

Screenshot from the Cool Walks App

The app might sound like just a little fun, but it has helped the team in Barcelona realise where there’s more need of shade. “We are working on the shade plan,” says Marc Montlleo, Director of Environmental Projects at Barcelona Regional, “studying the areas where more shade is needed. This will primarily be solved with vegetation and if not with, photovoltaic pergolas or with ephemeral shades systems.” In the meantime, if someone is interested in developing the ‘Cool Walks App’ further, they can. In fact, the code is available for download, and people can access the links to all public data sets.

Blue gold

In Budapest, people don’t even have to download an extra app to get some helpful information on keeping the heat at bay. The ‘cooling islands’ are included in a map that people can access using the Fäder app, the same app they use to plan their journey with public transport. On the same map, users can also see where to find the nearest drinking fountain in the city.

“We realised that the city centre lacked drinkable water fountains while it is one of the areas most exposed to the heat island effect,” says Barsi. Access to free drinking water is another crucial way cities can help their population to fight extreme heat.

In the last two years, Budapest added 34 new water sources in the city centre. They also took inspiration from a previous solution and made it more sustainable. In the past, the city organised free distribution of plastic water bags during very hot days.

“Together with the drinking water company, we developed a vehicle which has a 500-litre tank filled with water and covered with solar panels to provide pressure for the small taps around it,” explains Barsi. “We bring it into highly populated areas, and people can fill up their water bottles for free. They love it.”

Mobile free drinking water distribution vehicle in Budapest

All good things come in threes, so Budapest brought free drinking water down to the depths of its metro stations. “Metro 3 is under reconstruction, and at the last moment, we considered adding free drinking water fountains in some stops,” says Barsi. “We talked with the transport company and checked that it was legally and technically possible. Now we have about 12 water taps installed underground in several metro stations.”

First steps

Budapest’s next move is to put together their experience with the instruments they have created and tested and develop a permanent protocol for dealing with heatwaves in the city.

Barcelona is also using its datasets to plan for more green solutions that will help to keep the city cooler. For example, the team analyses material and structural soundness of roofs to estimate how many could be transformed into green roofs. “We have been working with green corridors modelling to map which parks are connected and which are fragmented,” adds Carbonell. Such models will be interesting for the city to decide where it is more strategic to add more vegetation.

While more comprehensive solutions are needed worldwide towards climate mitigation to limit the frequency of extreme high-temperature events, cities can already take small steps to protect their residents and bring them a little relief during the next heatwave.


Wilma Dragonetti Eurocities Writer