Urban climate change

The climate in towns and cities differs vastly from that of outlying areas. One reason lies in the anthropogenic change in the climate and the air quality. The key causes are due to a high degree of soil sealing, dense building developments and emissions from industry and traffic in heavily built-up areas.

The pace of climate change is making these factors worse, which is a big problem for the quality of life in towns and cities on hot summer days. Because of their diverse ecosystem services, green roofs are a fundamental way of adapting to climate change.

Climate change is occurring

The direct consequences of climate change are being felt the world over. Rising temperatures mean more hot days and warm and uncomfortable nights. Heavy, local rainfall frequently causes overflowing sewers and flooding. This poses an acute threat especially to life in towns and cities and the associated infrastructure.

Climate forecasts by the UN predict that the climate emergency will worsen in the next few decades. Steps must be taken today to maintain the quality of life in areas where people live.


Various climate scenarios highlight the dramatic increase in very hot days. As hotter air can absorb more water vapour, the length and intensity of dry spells will increase. The result will be less precipitation in summer.

Heatwaves that lasted 5 days at the end of the 20th century will last twice as long at the end of the 21st century, even if significant climate protection measures are taken. What’s more, they will last over 20 days if little is done.

Fig. 1: Changes in hot days and tropical nights in Europe between 2071-2100 compared with the control period from 1961 to 1990 (Fischer und Schär 2010); © ZAMG

Heavy rain

Climate change and rising temperatures lead to much heavier rainfall and encourage heavy rainfall locally, while the number of days where precipitation occurs decreases. Therefore, rainfall will occur less frequently, but will be heavier.

Alongside an increase in average intensity, climate scenarios predict that rainfall will be more variable. This means that the quantity of rainfall can fluctuate significantly from day to day.

Fig. 2: Simulated changes in heavy rain from 2071 to 2100 compared with the control period of 1961 to 1990; © European Communities 2008

Urban areas as the drivers of climate change

Some fundamental processes that shape the urban climate are also responsible for climate change globally. This includes the high level of soil sealing, greater energy consumption and higher greenhouse gas emissions in urban areas than in outlying areas. The urban heat island effect is a typical phenomenon of the urban climate and helps heat up the planet as well.

The heat island effect is defined as the difference in air temperature between the hotter urban area and its cooler outlying areas. The biggest difference is reached on a cloudless, windless night. Temperature differences of up to 10°C between urban cores and their environs are already being measured today.

This phenomenon occurs in almost every urban area, regardless of whether it’s big or small or located in a hot or cold climate.

Widespread soil sealing in urban areas is the main cause. The impervious surfaces heat up during the day and emit heat at night. They also prevent natural rainwater run-off, which reduces evaporation significantly. Evaporation removes heat from the ambient air, which leads to less cooling and lower humidity in the urban area.

Fig. 3: Heat island effect in Stuttgart based on ground temperature (blue line); © Landeshauptstadt Stuttgart, Amt für Umweltschutz, Abt. Stadtklimatologie

Urban areas affected by climate change

UN forecasts predict that almost 70% of the world’s population will live in urban areas by 2050. This urbanisation will accelerate the urban heat island effect and, together with global warming, lead to problems with water such as flooding and shortages.

Flooding is a serious problem, especially in towns and cities. It’s also expected to worsen in the wake of global climate change, due to more intense rainfall and faster runoff in increasingly urban landscapes.

The high level of soil sealing in urban areas is one of the main reasons for this effect. It disrupts the natural water cycle by preventing infiltration and evaporation of rainwater. As a result, during heavy rainfall, urban sewers can’t cope and heat islands form in hotter periods.

In the future, the urban climate will be affected by more heat in summer due to climate change and entail an increase in more intense heatwaves that last longer.

Skyline - Stadtklima im Wandel

Suitner, Johannes; Hofinger, Johannes; Sparlinek, Fabian; Stadtentwicklung and Stadtplanung, Ma 18 (2020): Klimasensible Stadtentwicklung: Eine Analyse international projects and measures hitzeangepasster urban development mit Anregungen für Vienna 2020, p.3. Retrieved here: Link

List of figures
Fig. 1: ZAMG Zentralanstalt für Meteorologie und Geodynamik (not dated): Hitze: Anzahl der warmen Nächte steigt. Retrieved here: Link

Fig. 2: Dankers R., Hiederer R. (2008): Extreme Temperatures and Precipitation in Europe: Analysis of a High-Resolution Climate Change Scenario. Office for Official Publications of the European Communities Luxembourg, p. 49. Retrieved here: Link 

Fig. 3: Landeshauptstadt Stuttgart, Amt für Umweltschutz, Abt. Stadtklimatologie (not dated): Der Wärmeinseleffekt (UHI). Retrieved here: Link