© Stadt Wien

Beating the heat in Vienna

As Europe scrambled to contain winter-induced coronavirus outbreaks towards the end of 2020, the news that last year was the joint-hottest year on record, holding the top spot with 2016, slipped by unnoticed. In the four years between these two landmark dates, people across Europe agreed: the summers were scorching.

Austria’s capital Vienna was no exception. The city recorded its hottest year in 2017 and temperatures have been markedly high during the summer months over the past four years.

In the summer of 2019, city employee Andrea Paukovits was sitting uncomfortably in her office in Vienna as the city suffered through its third day in a row with temperatures above 30 degrees Celsius.

The city’s Neo-Gothic town hall was not built to withstand temperatures 10 degrees hotter than the average maximum for that time of year, and the Viennese even less so. “We’re not good at coping with heat. We’re not Italian!” she says.

Suddenly, Paukovits’ boss Ulli Sima spoke up. “We have to do something!” she declared. The uncharacteristic heat had finally broken the city government’s councillor for the environment.

Discovering the heat islands

What happened next would be the start of a popular cooling measure that would bring some relief to the overheating Viennese. “She called our departments that are responsible for this, and in two days they had the first fog showers installed,” recalls Paukovits. “They were initially very home-made, but they then became more professional.”

The fog showers spray a fine mist into the air to cool down passers-by and were tactically placed in some of the warmest public spots, such as the sizzling concrete expanse of the Schwarzenbergplatz. Alongside mobile water fountains and an app to locate the coolest spots in the city, the measure was a major weapon in the “war on heat islands”, according to Councillor Sima.

We have to fight climate change, but we have to adapt to climate change that is already here. We have to work on two levels.
— Andrea Paukovits, City of Vienna

The “heat islands” that Sima refers to are a product of the rising temperatures: human activity, concrete, asphalt and pollution all drive up the temperature in a city by as much as five degrees compared to the countryside.

“You have less vegetation in the central districts of the city with more asphalt and concrete surfaces,” says Philipp Weihs, lecturer at the Institute for Meteorology and Climatology at BOKU – Vienna’s University of Natural Resources and Life Sciences. “These surfaces absorb the heat, store it and reflect less radiation – all this excess heat leads to a higher surface temperature and higher air temperature.”

This meteorological effect has a real impact on city-dwellers. It can range from general discomfort to respiratory problems, exhaustion and headaches, with children and older people at a higher risk of heatstroke and increased mortality. Paukovits also notes the psychological effect: “I don’t know if there are some studies, but the aggression levels rise. Hot summers are not good in the city.”

Planning for a warm future

With climate change undeniably causing an increasing number of problems in Vienna, the city decided to implement an urban heat island strategy including measures like the fog showers and fountains to mitigate the hot temperatures. The strategy would complement the more general climate change strategy. “We have to fight climate change, but we have to adapt to climate change that is already here. We have to work on two levels,” says Paukovits. What’s more, Vienna’s residents seem to understand that the two plans are linked. There is little resistance to the city rolling out the cooling measures because they see them as necessary.

Vienna’s transformation into a city ready for climate change was helped by BOKU. Weihs says that the university worked with the city on a climate-friendly urban planning project, testing possible solutions to get the city ready for rising temperatures.

“One simulation was to improve the characteristics of the buildings – improving the insulation, increasing the reflectance of the building, and at the same time increasing the density,” says Weihs. This means that more inhabitants could make use of the building’s cellars and lofts. Overall, the university found that this scenario was the most climate-friendly approach the city could take.

“Of course,” add Weihs, “we did not change vegetation in the simulation. Vegetation is very important.” The addition of trees and green spaces, known as greening, is also crucial in the fight against heat. While more than 50 percent of the metropolitan area is made up of green spaces, it is unequally distributed, with residents living in poorer, inner-city neighbourhoods benefiting from less access to green spaces than the more well-off or suburban Viennese. “For people, it’s really important to have some locations where you have shade,” says Weihs.

This is an issue that the city has picked up on. The urban heat island strategy also focusses on planting trees and making the façades of Vienna’s boulevards into a haven for plant life, as simulated in attractive mock-up photos provided by the city. “We know it’s not enough to just spray some water in the air, and of course more greening and planting of trees also combats climate change,” says Paukovits.

Sleepless nights

Despite an ambitious plan, installing fog showers and water fountains will not solve all the issues caused by heat islands. “The problem isn’t really during the day. You have enough possibilities to cool down,” says Weihs. “The problem is more during the night.” City-dwellers in areas where there is a low amount of vegetation and very little movement of the air will experience much higher temperatures during the night than their neighbours in leafy environs, leading to associated health problems and an uncomfortable night’s sleep.

Solving the issue of warm night-time temperatures requires more invasive measures than fog showers or water fountains, such as increasing the insulation of buildings. “That means there will be less heat transferred indoors and less heat stored during the day,” explains Weihs. Vienna’s heat island strategy mentions insulation as a key tool in beating the heat but retrofitting many of the city’s Baroque buildings will be challenging, if not impossible.

With another warm summer on the horizon, Vienna is ready. Its 172 fog showers, 15 mobile fountains and an increasing number of fixed water features are ready to cool down the heat-averse Viennese. And with a new Socialist-Liberal government appointed in November looking to take a robust approach to climate change, the heat island strategy looks like it will live on.

For Paukovits, the measures the city took in 2019 are well worth the modest cost and have even attracted interest from other European cities. “We already have some cities asking us where to get some of these fog showers,” Paukovits says. “People love it and it’s not expensive. It’s a win-win.”

More information on Vienna’s heat island strategy can be found here