„Weather as in Florence“: Vienna plans its climate future until 2100

Temperatures have reached 36 degrees in Vienna. The air above the city’s asphalt is flickering. Elderly people wait exhausted at a small bus stop. Otherwise the streets are almost empty. In some areas there are only a few protecting trees or fountains. If you can, you don't go out at all. When midsummer reaches the Austrian capital, life in some parts almost comes to a standstill.


An evening thermal image of Vienna. The streets are clearly visible because of their high temperature
Evening thermal image of the city of Vienna. The hot (red) areas are clearly visible in comparison to the cooler surroundings (blue).


In “Biotope-City”, a newly planned construction project in the 1.9 million-inhabitant city of Vienna, things will be different. When the hot southern winds meet the buildings here on a summer day, they are cooled down about three degrees.

The reason for this is the extensive consideration of green areas. The residential project, which is scheduled for completion in 2019, will improve the quality of life and protect the city better against extreme weather conditions.


"We want to know the climate of whole Vienna"


"A project like this is great for its immediate environment. But we are interested in what would happen if we implemented such projects all over the city. We want to know how the climate of the whole city is influenced" Florian Reinwald is a senior scientist at the institute for landscape planning at the University of Natural Resources and Life Sciences (BOKU). He is in charge of the project “Green.Resilient.City”, which has set itself the task of planning the climate of the entire city.

This could still be a hard way. While green spaces are mandatory for new construction projects in metropolises all over the world, Vienna has rated green areas desirable but optional. The reason is the stock of many buildings from the Viennese “Gründerzeit” of the late 19th and early 20th century. The result has been that wild flowers in districts such as the "Kreta" were seen at best when they were painted with chalk on a free parking lot.


Green spaces for big cities


BOKU has therefore created the "green and open space factor". As in other cities, it is intended to establish a mandatory proportion of green infrastructure in new construction projects. It includes roof gardens, green facades or trees on the streets of the city. "However, we are taking it a decisive step forward," says Florian Reinwald.

In collaboration with the Austrian national weather service “ZAMG”, researchers at BOKU have created an instrument with which the effects of all green space projects can be simulated. "What effect would it have if we had ten percent more green spaces in the city," asks Reinwald. "So we are not just specifying a percentage of green spaces, we are linking them directly to the city's climate targets.

It doesn’t end there either, because not only the current climate situation is forecast, but also future ones. The “Austrian Institute of Technology” (AIT) provides a simulation where the future climate of Vienna can be outlined. “This enables us to calculate the impacts of our city planning up to the years 2050 or 2100”, says Reinwald. Numerous studies show how important this step is. "There are simulations that predict Vienna in 2050 to have a climate similar to that in Florence.”


Green.Resilient.City: Projects in the new and old parts of Vienna


This instrument is already tested in two parts of Vienna. In the densely built-up district of “Kreta” and in a new urban development area in the southeast of Vienna called “Seestadt”.


New buildings in the city development area "Seestadt" in Vienna


The city development area “Seestadt” is one of the largest urban development projects in Europe since 2010. Within 20 years, a completely new district is to be built in which more than 20,000 people live and work. The first of three development stages is concentrated in the south of the district and is scheduled for completion by 2020.

The northern side, on the other hand, is still largely in the planning stage. In an international urban planning competition, BOKU has been given the opportunity to test the green and open space factor. "To be eligible for the construction project, at least 60 percent of the area used must have green infrastructure," says Reinwald. In a second step, the six finalists of the competition will then be examined by the partner project "green4cities". It’s instrument “Greenpass” (powered by ENVI-met) calculates the impact of construction projects on the climate around the new buildings and can also give recommendations for optimization.


Red and green colors show differences in air temperature on a simulated picture of the new urban development area "Seestadt" in Vienna.


"Green areas are not accepted by everybody."


The situation couldn’t be more different in the district “Kreta”. In this densely built-up area there are still many buildings from the Viennese “Gründerzeit”. At that time little thought was given to green and open spaces. Heat waves and extreme rainfall hit this quarter particularly hard today.

"How do we manage to hold back extreme precipitation for as long as possible so that we don't have to build additional sewers or sewage treatment plants?", Reinwald outlines one major problem. "Green areas and open spaces can improve a lot here. But it is much more difficult to proceed in grown structures. The fact that more green space is accepted by everyone everywhere is a fallacy.”


In a climate-friendly city, everybody is involved


Roof gardens and greening facades often seem like a great step to climate change adaption. However, many legal questions arise here. Who is liable if part of the facade greening falls off? Who maintains the green area? Who pays for the renovation of the wall and who pays for the project? "In buildings with condominiums, the problem is even greater," says Reinwald. "Here the decision must be made unanimously.”

However, Florian Reinwald is observing a rethinking in the population. "In combination with the increasing heat and the strong city growth, with the loss of green spaces and open spaces, the Viennese are becoming a little bit more sensitive to this topic," Reinwald laughs. Nonetheless, a successful climate strategy can only be successful if the population wants it to be. "That's where it needs us as researchers, that's where the population is needed, and that's where the city administration needs to be. We are working within this triangle".



University of Natural Resources and Life Sciences Vienna - Institute for Landscape Planning and Institute for Landscape Development, Recreation and Nature Conservation Planning

green4cities GmbH


AIT - Project Green.Resilient.City

wien3420 – Seestadt Aspern

Environmental Protection in Vienna - Municipial Department 22 -