Urban Physics
Tampere University
Global Urban Population
Currently, around 56% of the global population – or around 4.4. billion people - live in urban areas. With the current rates of urbanization, the global urban population is expected to double by around 2050 when 70% of the world’s population is predicted to live in cities.
The way in which our cities are designed and built can have significant implications for the environment. Growing cities face demands for land which can lead to urban sprawl (or the expansion of the geographic extent of cities) and urban land expansion can outpace population growth by as much as 50% . Urban areas also have significant demands for energy and resources, and currently account for more than 70% of global greenhouse gas emissions .
Credit: Global Human Settlements, Urban Centres Database
Carbon emissions
Human emissions of carbon dioxide and other greenhouse gases have been increasing since the industrial revolution, primarily through the burning of fossil fuels such as coal, oil, and natural gas. These gases are strengthening the greenhouse effect, trapping heat in the earth’s atmosphere, and are “ extremely likely to have been the dominant cause of the observed warming since the mid-20 th century ”.
This changing climate is leading to a number of impacts, including extreme weather events that can affect our health, and these impacts will continue to worsen as the climate changes. It is therefore critical that we urgently reduce our greenhouse gas emissions to limit (or ‘mitigate’) the degree to which the climate changes.
The good news is that many countries are making progress on reducing emissions – but we need to do much more and act much faster.
Urban Environmental Health
The way we design and use our urban environments also presents residents with specific health risks. These include exposures to environmental conditions that can make us uncomfortable or harm our health, such as:
Illustrations: Future London by Ramon Mendoza
Extreme temperatures and heat waves
Climate change is increasing the frequency of hot weather events, and the Urban Heat Island effect can mean temperatures can be higher in cities. This heat exposure can impact our health - for example, the heatwave in 2022 in Europe led to an estimated 15,000 excess deaths .
The way in which we design our cities and buildings can help adapt them to future climates with more extreme heat events. This can include replacing human-made materials in cities with natural greenspace like trees and grass, and designing our buildings for hotter conditions.
Air Pollution
Air pollution is emitted in cities from anthropogenic sources like traffic, industry, and energy production in powerplants or in households that burn solid fuels. Around 96% of the EU's urban population lives in areas where outdoor air pollution levels exceed World Health Organisation guideline levels, and exposure to fine particulate air pollution is estimated to cause 238,000 premature deaths in the EU every year.
By designing our cities in ways which reduce or remove sources of air pollution, we can make a substantial improvement to population health.
Wind
The movement of wind through cities is influenced by, for example, the height and shape of buildings. The buildings can cause phenomena such as wind canyons and downdraught effects, that can make it uncomfortable or even dangerous for pedestrians at street-level because of high wind speeds. Wind can also help remove air pollution and heat. At the same time, building structures need to be resilient to wind pressures and wind-driven rain.
Understanding the role of buildings on wind (and vice-versa) is an important consideration in urban design.
Noise Pollution
Noise Pollution comes from anthropogenic sources such as traffic, aircraft, construction, and industry. Long-term exposure to noise can affect sleep, the cardiovascular and metabolic system, and can lead to cognitive impairment in children. In Europe, noise pollution is estimated to cause 12,000 premature deaths, 22 million cases of chronic high annoyance, and 6.5 million cases of chronic high sleep disturbance each year.
As with air pollution, removing sources is the best action we can take in cities, while the types of materials we use and structures we build can also reduce noise pollution. By reducing or removing unwanted sounds - and enabling sounds we want - we can improve urban soundscapes and population health and wellbeing.
Light Pollution
While light is important for safety in cities, light pollution comes from excess use of artificial light. It is estimated that 82% of the global population lives under a light-polluted night sky. The height of buildings can also impact the availability of direct solar radiation in cities.
Light pollution may have a number of health effects including causing sleeping disorders, depressive symptoms, and cancers . It also leads to excess use of energy. Better lighting designs in cities can help to reduce this light pollution.
Urban Energy
Cities are also critical areas for helping to mitigate climate change because of the concentration of people and infrastructure, and the disproportionate amount of global emissions.
The way in which we design and use our urban environments can influence the amount and types of energy that we consume, for example:
Fossil Fuel Energy
Fossil fuels are burnt to produce energy in power stations, to power automobiles and industry, and to heat homes, for example. These fuels include coal, natural gas, petroleum and oil. Burning these fuels produces greenhouses gases, and is the primary cause of climate change.
Burning these fuels is also a major source of harmful air pollution. Air pollution from the burning of fossil fuels is estimated to cause around 8 million deaths every year across the globe. Thus, moving away from fossil fuels is critical for both the climate and health.
Renewable Energy
Alternatively, we can shift towards using cleaner energy sources such as solar or wind energy which do not produce greenhouse gas emissions or air pollution.
Reducing energy demand through improved efficiency is another important way to reduce emissions. Improving sufficiency - or changing behaviours to reduce energy consumption - is also critical.
Urban Form
The energy consumed and the environmental conditions in cities can depend on the urban form. Studying the role of the urban environment on these phenomena can help us design cities to reduce our energy consumption and exposures now and in the future.
This requires having a good understanding of the urban environment, which can include:
Roads
Traffic on roads is a source of air and noise pollution. Using both measurements and modelling methods, it is possible to get an idea of how air pollution can disperse around the city. Similarly, the propogation of traffic noise can also be measured and modelled.
Asphalt pavement, and other dark surfaces, are a primary cause of the Urban Heat Island as they absorb and retain heat more than natural materials.
Buildings
Buildings influence outdoor conditions in urban environments, for example:
- Climate (by absorbing heat, producing waste heat, or blocking solar radiation)
- Wind flow around buildings, and how this wind can disperse pollution and heat
- Daylight and solar radiation from the buildings' shadow
- Absorption of noise pollution
- Air pollution, if the building itself is a source - such as industry or the burning of household fuels.
The way that buildings are designed, constructed, and used also modifes occupants' exposure to environmental hazards from indoor or outdoor sources. This is important because of the amount of time we spend indoors during our lives.
Greenspace and Bluespace
Greenspace like parks and forest, and bluespace like lakes and rivers also influence the urban environment. They help reduce urban temperatures because they do not absorb heat the same way human-made materials do, and help cool the air through evapotranspiration. Trees can also provide shade and in some cases can help reduce air pollution.
Designing Cities
Adaptation
The frequency of climate-related environmental hazards has been increasing in recent years, and will continue to increase in the future.
The question is not just how we mitigate climate change – but also how we adapt to the inevitable changes that will occur in the future.
Bioclimatic Projections. Credit: WorldClim
Resilience
Climate resilience means having the systems in place to cope with climate-related hazards. From a built environment perspective, this means designing cities, buildings, and infrastructure for a future climate.
By understanding how climate change will worsen current climate-related risks and lead to new risks, cities are able to take action to adapt and reduce their vulnerability. These decisions can be based on scientific evidence that shows how urban environments can alter the exposure to different risks.
Lock-In
It also means avoiding poorly designed infrastructure and land use. Investing in poor infrastructure can lead to "carbon lock-in", or greenhouse gas emissions that as long as the infrastructure is operating.
Because of the expense of replacing infrastructure, this lock-in can sometimes last for generations, and can delay or prevent the transition to low carbon alternatives.
Cities therefore need to make the best possible decisions on infrastructure using available evidence.
Urban Physics
A number of different disciplines study use an engineering or scientific approach to study these energy and environmental challenges in cities. These include for example, urban climatologists, aerodynamicists, Geographic Information Scientists, Architectural Engineers, and statisticians. Bert Blocken has defined it as :
“The science and engineering of physical processes in urban areas”
The idea behind urban physics is quite new, and refers to the broad group of scientists and researchers using science and engineering to help design outdoor and indoor urban environments that are energy and resource efficient, as well as healthy and comfortable for people.
By understanding the physical processes behind urban phenomena, we can develop models which helps us predict how energy use and urban environmental conditions can change in the future given different climate, energetic, societal, and urban development pathways.
Our Research
At Tampere University, we research air pollution and urban heat exposure in particular.
Take heat exposure in London, UK, for example. If we want to know how temperature varies across a city we can collect temperatures from:
Weather Stations
This can include official weather stations, which provide highly accurate measurements of temperature and related weather variables.
It can also include private citizen weather stations which are less accurate but provide much better spatial coverage in many cities.
Climate Models
Alternatively, we can use urban climate modelling approaches.
These can be mesoscale models , which can cover areas hundreds of kilometers wide and which account for the different types of land cover and the height of buildings.
Or, they can be microscale models which can cover areas of less than 1km, and which give highly detailed estimates of temperature based on highly detailed inputs of the materials and 3D urban form.
Building Physics
Buildings can respond very differently to heat depending on their design and construction.
Using data on how buildings are constructed in a city, we can use building physics models to understand how buildings can vary in terms of their overheating risk.
If we know where these different types of buildings are located, we can examine how they may modify the population exposure to harmful heat given local outdoor temperatures.
Adaptation
If we want to study how to reduce heat exposure, we can run new climate and building physics models.
For example , it is possible to explore how increased urban greening can reduce urban heat island temperatures by re-running urban climate models, adjusting different land types to represent greening scenarios.
And, we can test how different housing adaptations such as changes to building energy efficiency or external window shutters may reduce indoor temperatures.
We can also use established models that relate heat exposure to health outcomes to estimate the health impacts of different scenarios.
Work with Us
We are open to new research collaborations and PhD students. If you are interested in working with us on any area related to Urban Physics, please get in touch with the link below.
The urban phenomena that we study have significant implications for population health, and in many cities around the world low income populations have a greater exposure to harmful environments. We therefore welcome collaborations with health experts and social scientists to help improve our understanding of how urban environments impact upon health and equity.
