Text: Sandra Pfeifer
Photos: Bernhard Scharf, Universität für Bodenkultur Wien
Without air there is no human life. The Austrian pavilion Breathe Austria at the EXPO in Milan highlights the importance of our number one staple food. But the latter is slowly turning into scarce commodity: With a projected 70% urban population growth until 2050, this not only brings a constant rise in greenhouse emissions, but also a higher demand in clean air and energy. Bernhard Scharf, head of the Institute of Soil Bioengineering and Landscape Construction at the University of Natural Resources and Life Sciences in Vienna, explains why the pavilion gives a good indication towards the green city of the future.
Well, we all know the predictions of the worldwide climate change scenarios and what to expect. The current downscaling model for Vienna forecasts an annual average temperature of 15 degrees Celsius for the year 2100 (currently, it’s 10 degrees). But that is only realistic if global average temperatures do not exceed 2 degrees above pre-industrial levels. With regards to the skills of building structures we have already reached the limit. The biggest potential lies outdoors in green infrastructures which is currently considered the most favourable solution around the world.
Idyllic images of a green sea of urban roofs come to mind. Is that a realistic scenario?
Yes. We can definitely plan and create green infrastructure. Green rooftops, in large dimensions, are highly effective: By means of photosynthesis they can process a lot of air immediately, providing us with the oxygen that is vital for us. Generally, it’s always about energy: You can’t destroy it, you can only transform it. And that’s what plants have been doing for millions of years – all by themselves, no microchips needed. They store and evaporate water. This means humidity for us, something we can really use on hot days. 100 to 150 m2 of living wall have the same evaporation as a 100-year-old beech tree – about 500 to 700 litres of water per day. If you think of that, you realize that plants are unbelievable all-rounders.
What are the challenges in the realization of this concept?
The denser a city and the higher its buildings, the larger the area of green facades has to be in relation to the city’s total surface. We call this the Leaf Area Index: green leaf area per unit ground area in m2. Of course this index is incredibly high in the pavilion because we optimized it. In urban areas, however, it is much more difficult. We would have to create roof gardens or green vertical areas. For urban residential buildings where, let’s say, 1,200 people live on a relatively small ground base, the green leaf area would have to be about ten times bigger. Theoretically, we do have the technologies needed for such an endeavour. Already last year, the European Commission has adopted the Green Infrastructure Strategy. I can only hope its implementation doesn’t fall through for financial reasons.
Breathe Austria provides the air for its visitors in real time. Could a city technically produce its own demand for air in the future?
Well, I think that would be rather difficult. Maybe with a really high proportion of green vertical areas…
What could be done towards climate change adaptation already today?
A start would be to identify sensitive areas of a city and see how green infrastructure could be created most effectively in these zones. In Vienna, these would be the first and second district and the industrial area of Inzersdorf. In order to maintain our thermal comfort in the long run we need to allow for enough time for the greening. We tend to think that it’s not as bad here because we are surrounded by the Alps, but that’s a fallacy.
Because the vital question is: How – and how sustainably – can we generate the energy needed for cooling? Air conditioning heats up urban space. In this regard, the Austrian pavilion is a vision of the future of the city: It cools itself by means of greening.
What difference will green cities really make?
Harry Glück, the Viennese architect, refers to it as the Appell der Natur (Nature’s Calling ie. the need to leave the city for greener pastures), because the quality of life in a city and how we feel about it is often not what we are looking for. But if we can provide it – decentralised, yet still within an urban context – so that people find recreation close by, this will lead to an increased quality of living, more contentment, and less traffic. We need intelligent solutions to create synergies between architecture and nature. Our pavilion gives a good indication of how this can be done.
Can we bring enough green into the city so that we will no longer have to rely on nature outside city gates?
We will never be able to replace a forest and all it contributes to our survival and atmosphere. But we can offset the perceived opposition of city and nature and understand cities as natural spaces. After all, mankind is nature.