It is hot in the city, and it is only going to get hotter. Fredrik Lindberg, researcher at the Department of Earth Sciences, knows how to reduce temperatures that are hazardous to health during heat waves.
“Large trees are the most important”, he says.
A biting wind crosses Stigbergstorget. That is what it is like when you live in Gothenburg, most of the time. Fredrik Lindberg pulls his woollen hat down over his forehead.
“Our research field finds itself in a catch-22 situation. We often have bad weather, the rain is horizontal and people at our latitudes need the Sun when it finally makes an appearance. At the same time, children, the elderly and people with heart and lung diseases are vulnerable. Who should we design the city for?” asks Fredrik rhetorically and then answers himself:
“We need to create a mosaic, a city that takes all the city’s residents into account.
A city is always warmer than the surrounding countryside. Particularly when the weather is fine. Researchers at the Department of Earth Sciences have measured a difference of 12 degrees between central Gothenburg and the countryside surrounding it.
“Yet our Swedish cities are small by global standards. And we are yet to start cooling our homes, which makes the outdoor climate in many cities even warmer due to the energy that is used for air conditioning,” says Fredrik.
As the global temperature rises, our cities will also get warmer. But the local climate is also affected by many other factors.
The location of the city – on the coast or inland – plays a role, as well has how it is designed. A long, narrow city with streets running north to south is cooler than a compact city with streets running from east to west where the Sun’s rays reach the ground for many hours of the day. The height of the buildings, how close they are to each other as well as what they are made of all have an effect. The trend towards higher density urban development is making cities even warmer. There is hardly any room for green spaces, which are essential.
“However the weather has the greatest impact. High pressure with little wind, only a few clouds and lots of sun generates heat stress. Not only does it lead to health problems, but it also has an impact on the efficiency of workers and the economy,” says Fredrik.
In addition, he points out, the urban heat island (see fact box) is a socio-economic problem given that not everyone is able to drive a car to the coast to cool down on hot days.
The Department of Earth Sciences is located on Medicinareberget. The research team is small: two to three senior researchers, a few postdocs and a handful of doctoral students.
The extreme heat in the summer of 2018 gave urban research an additional boost. The knowledge acquired by Fredrik Lindberg and his colleagues is now in demand.
“Making it available to others is important,” he says.
In addition to mapping the local climate in different districts, the geoscientists are developing practical tools for others. Urban planners and architects need their help to build a more attractive city.
“It’s exciting when you see that they are starting to use what we have developed. And they are doing so more and more!”
From previously working a lot with field measurements, often in combination with interview studies and observations to see how people experience the environment they live and move around in, another method has gradually started to take over: climate modelling.
So what can be done about increasingly warm cities?
Material and colour choices and geometry play a part. Even more important are the water and green spaces of blue-green infrastructure. How the green spaces element is designed has a range of different effects:
- GREEN SPACES. “A large park can have positive effects several hundred metres into the city blocks around it.”
- TREES IN THE STREETSCAPE. “Shade means that the elderly and young children can be outside more. In addition, the asphalt does not heat up. Really big trees, like those that enclose the entire streetscape in Berlin and Hamburg, also have a cooling effect through transpiration.”
- GRASSY AREAS “Grass does not heat up as much as asphalt and retains water in a different way to paved surfaces. It should not be forgotten that different surfaces can be combined. For example, you can lay grass between tram tracks.”
- INFORMAL VEGETATION. “With higher density development, a lot of the informal vegetation disappears, for example, when hillsides are removed. The informal vegetation is threatened while formal vegetation is protected. A garden bed has very little impact on the local climate.”
- GREEN ROOFS AND WALLS. “They may be nice but they impact the indoor climate a lot more than the outdoor climate. For that, trees are much more efficient.”
One concern is that measures to lower temperatures can be counterproductive. Tall buildings for example. They provide more shade at the street level, but they make it harder for the heat to escape overnight. Boulevards with large trees provide lovely places to walk and lower the temperature but they can prevent air pollution from lifting. That’s why it’s important to combine and diversify the measures.
“A compact city and a green city must go hand in hand,” says Fredrik Lindberg.
The urban heat island
This is a key concept in urban climate research. An urban heat island means that a big city is significantly warmer than its surroundings, particularly at night. It was the ‘father of meteorology’, British scientist Luke Howard, who discovered this phenomenon in London in the early 1800s.
Urban climate research for healthier cities
WHAT Urban climatology focuses on how the local climate, air quality and the perceived temperature in urban environments is affected by buildings, green structures and land use. It includes everything from basic research to developing tools for architects and urban planners. It is an interdisciplinary subject area.
WHEN The University of Gothenburg has been conducting urban climate research since the 1970s. Fredrik Lindberg is currently leading a project on the effects of heat waves on preschool children, for which Master’s student Oskar Bäcklin has studied 438 preschool yards in Gothenburg. Most of them did not have adequate shade.
WHY With climate change and increasing urban settlement, the problems brought on by urban heat islands are increasing. By integrating climate science into urban planning and architectural design, it is possible to build a healthier and more attractive city.
Position: Researcher in Earth Sciences specialising in urban climatology.
In the spotlight because: He is currently working on producing a modelling tool and identifying measures to reduce heat stress in future heat waves.