Urban Heat Vulnerability Assessment of Vienna, Austria


Between 1961 and 1990, Vienna experienced on average 9.6 heat days per year. From 1981 to 2010, the number of heat days rose to 15. According to forecasts, there will be an average of 19 hot days between 2021 and 2050, and 41 between 2071 and 2100. Moreover, the population is expected to increase from 1.8 million to 2 million by 2029. To protect the population from the consequences of heat events, the Energy Planning department of Vienna decided to take action.

Our methodology


We study the urban needs.


We define relevant indices to take into consideration for heat assessment.


Measured by studying and quantifying the occurence of high temperatures within the city between 2015 and 2019


Measured by studying the population density of individual particularly sensitive to heat: younger than 17 and older than 65 in this project

Adaptive Capacity

Measured by identifying greeneries and water-bodies. It represents the ability of the ecosystem to cope with heat events


Based on our algorithm, we map the sub-indices and combine them to create the Urban Heat Vulnerability Map.


We customise environmental solutions to cool down critical hotspots.


Implementation of vegetation (trees, grass, green roofs and walls) creating protective shadows and evapotranspiration. 


Implementation of water bodies within urban areas, acting like a heat captor to cool the city and improve the quality of life.

Brighten up

Implementation of different materials, colors, as well as shapes of structures and buildings to uptake heat from solar radiations.

Results and actions

Without any action, + 8°C by 2050
The top 10 districts have been ranked based on their average Urban Heat Vulnerability Index. These districts  present a very little vegetation. The map also shows that even in less urbanized areas, heat vulnerability points are likely to appear. Through the study, we found that by 2050, Vienna will heat up to 8 degrees if no action is taken. 
The Cool Streets project

Vienna is developing „Cool Streets“: places for people to stay outdoors, play games, and socialise. This program intends to provide additional seating, cooling systems such as mist showers and establish parking ban to allow citizens enjoy the city at its best. After interviewing 518 citizens results showed that „Cool Streets“ was a great success and should be continued next year. The municipality plans to extend this measure to all 23 Viennese districts.

“For the first time we have a map that shows us where cooling is urgent and allows us to take specific measures.”
Birgit Hebein
Former deputy major, City of Vienna
“We have been collaborating with ECOTEN in the field of sustainability and ecology and we are not surprised that Vienna chose to work with them as well.”
Tomáš Ctibor
Founder & Exectuive Director at 4ct

Download the full report for free

Learn how we collaborated with the City of Vienna to fight against extreme heat impacts.

In this report, you will find:

  • A detail presentation of our methodology
  • The full range of maps used for the Urban Heat Vulnerability Assessment of Vienna
  • The ranking of the most vulnerable Urban Districts
  • Our guidance and the strategy adopted by the City of Vienna