A Blog post by Leonard Horn

Key Words:

Climate Change

Urban Heat

Equality

Ecosystem Services

Urban Greenery

Sustainable Development Goal (SDG) 3

Sustainable Development Goal (SDG) 11

Heat, Ecosystems and Equality within the City Landscape

Experiences and Learnings from a Fieldtrip to Vienna and Bratislava

Heat, as one environmental problem cities face, is much more than just the temperatures being hot. It poses a high risk for vulnerable groups and is one of the deadliest natural hazards urban populations are facing. Whilst urban greenery is a very effective measure for regulating the urban climate, its distribution and access for residents is unequal and needs to be improved both in Vienna and Bratislava. The reintegration of ecosystem services within the cityscape is crucial for dealing with this hazard and might have a big impact in dealing with environmental as well as social challenges cities are facing today and increase their overall resilience. It will be the challenge of urban planners as well as the people of the city to reintegrate nature and ecosystems within the city landscape.

I got off the Railjet that brought me conveniently from Innsbruck to Vienna within a few hours with high speed and air conditioning. It was a sunny and hot day in the middle of July, and when I left the main station, the heat was intense with the sun reflecting from the metal and glass surfaces of the highrise buildings and being absorbed by concrete structures and asphalt pavements. There were no trees that could provide shade, only a tower with drinking water and a button for a cooling spray of mist. This was my first impression from Vienna, which I visited during the field trip ‘Vienna & Bratislava: Twin Cities or neighbours by chance?’, in which I participated as part of my Geography Bachelor at the University of Innsbruck. Over the span of eight days, we would be visiting locations in Vienna and in its neighbouring City Bratislava as well as in the region between the two cities and talk about a multitude of topics with a focus on spatial and urban planning. On most of the days we were confronted with one of the challenges large urban areas are facing, especially due to overall rising temperatures: urban heat. A heat wave happened while we were on our field trip, which lasted for a total of 18 days, reaching temperatures over 30°C at daytime and bringing tropical nights in which the temperatures wouldn’t drop below 20°C. In Europe heat waves can be counted as one of the most severe natural hazards in terms of the number of deaths which can result from them [1]. So, while we were saved from the heat by the fans in the hotel room at night, at daytime while out and about we coped with the heat by looking for certain places to stop and talk. Those would be shaded, preferably by trees, and in those green spaces, we could feel a great difference in temperature. Yet those spots were only sporadically spread over the layout of the city streets in both cities. Consequently, to me the question arose: What is the role of ecosystems in the city and how are they connected to urban challenges such as the urban heat island effect?

Apart from differences in temperatures on a small scale within the urban landscape, such differences also exist between the cities and their surrounding countryside. Cities heat up more due to their morphology, which describes the structure and materials of the cityscape: a dense layout of buildings of metal, glass and concrete as well as a high degree of soil sealing and only little vegetation cover. This difference in land cover can be seen in Figure 1. Therefore the temperatures in cities can get up to 4,5°C higher than in the surrounding countryside. This is described as the urban heat island effect [2]. Vegetation is crucial for the local climate conditions as of their cooling effect through shade and evapotranspiration. Furthermore, vegetation and soil increase the water retention capacity and bind dust and thus provide a better air quality. It also provides a space for social interaction and community building [3;4]. This climate regulation through vegetation can therefore be regarded as an ecosystem service. Ecosystem services describe the uses of a functioning element of the ecosystem for the human and the society. It is a concept, which links an economic value to the ecosystems. It can be criticized for commodifying the ecosystem, yet it is useful for it uses the prevalent language of economics for signifying their value to society. Ecosystem services include provisioning services like food and water supply, regulating services like climate and hydrological regulation and cultural functions like recreation [4].

The phenomena of urban heat can be used as an example for some urban problems being the result of a lack of ecosystem services within the cityscape, and therefore having the potential to be mitigated at least in part by the reintegration of greenery into the urban landscape. The loss of ecosystem services in the city is the result of their structure, as they are compact bodies of buildings and roads, which have developed over time to increasingly externalise many ecosystem services to the surrounding region and today even to other countries and continents, as is in part the case with the production of food. This has also enforced the perception, that cities are not part of the ecosystem as the ecosystem services are removed from the surrounding environment of the residents and therefore from perception. Yet they are, and this trend has created vulnerabilities as well as decreased resilience towards shocks like natural hazards such as heatwaves. Risks might also increase due to the climate change, as heat waves, droughts, storms and extreme precipitation events become more frequent and severe. At the same time vulnerabilities might increase due to social changes within cities [6;3]. Furthermore, social and environmental problems are closely linked to a lack of ecosystem services within or close to the city. This can be seen as a problem of environmental justice, as marginal groups with lower income usually face worse environmental conditions than high income residents [5]. Heat does also affect those who are vulnerable, mostly elder people living on their own and lacking a social safety net [6;7]. In Bratislava we visited the district Petržalka with about 100.000 inhabitants, where the population ages simultaneously, which might prove to be a problem in the near future concerning their coping ability to heat waves.

Spaces of urban greenery are not evenly distributed throughout the cityscape. This is the case in Vienna as a working paper from the BOKU examined looking at the equality of the distribution of green spaces. More than a third of the city’s residents do not have any greenery withing 250 meters of their homes, even though Vienna has a total of 66m² of green space per resident [8]. Bratislava has an even higher amount of green space per resident of 220m², yet the distribution and continuity of those spaces is comparable to Vienna [4]. Many of those spaces are also dedicated to urban development because of the city’s rapid growth, which might put them at risk. Both cities, Vienna and Bratislava, have formulated their intentions to increase the amount of urban greenery [9; 4]. On our visit we have seen some positive examples of their implementation, for example, at the Mariahilfer Straße and surrounding streets in Vienna, as shown in Figure 2, and the greening at the Danube waterfront in Bratislava. Yet we learn from Clarissa Knehs from the Department MA19 for Architecture and Urban Planning in Vienna, that the implementations of such projects face a multitude of obstacles. These include the political will and the negotiation between a multitude of different stakeholders, the partially high costs for construction and maintenance, as well as urban planning obstacles such as subway lines and underground pipelines which limit the space for the roots of trees.

Greenery within the urban context is of extreme importance. It has a multitude of benefits like the buffering of natural hazards such as heat waves and the improvement of the overall quality of life for residents. Therefore, it also must be taken into account when talking about the mixed functions of city quarters. Implementations today will decide how their cities will face global change in the future.

Literature

[1] Robine, J. M.; Cheung, S. L. K.;  Le Roy, S.; Van Oyen, H.; Griffiths, C.; Michel, J. P. & Herrmann, F. R. (2008): Death toll exceeded 70,000 in Europe during the summer of 2003, Comptes Rendus Biologies, 331(2): 171-178. doi:10.1016/j.crvi.2007.12.001.

[2] Organisation for Economic Co-operation Development (2010): Cities and Climate Change. OECD Publishing, Paris.

[3] Rosenzweig, C. Solecki, W. D.; Hammer, S. A.; Mehrotra, S.; Rosenzweig, C. & Solecki, W. D. (2011): Climate Change and Cities. Cambridge University Press, Cambridge. doi:10.1017/CBO9780511783142.

[4] Belčáková, I.; Slámová, M. & Demovičová, Z. (2022): Importance of Urban Green Areas in the Context of Current and Future Global Changes: Lessons Learned from a Case Study in Bratislava (Slovakia). Sustainability, 14(22). doi:10.3390/su142214740.

[5] Stache, E.; Jonkers, H. & Ottelé, M. (2018): Integration of Ecosystem Services in the Structure of the City is Essential for Urban Sustainability. In: Achal, V. & Mukherjee, A. (ed.): Ecological Wisdom Inspired Restoration Engineering. 1. edition. Springer Singapore Pte. Limited, Singapore.

[6] Benton-Short, L. & Short, J. R. (2008): Cities and nature. 1. edition. Routlege, London and New York.

[7] Ibarrarán, M. E.; Ruth, M.; Ahmad, S. & London, M. (2009): Climate change and natural disasters: macroeconomic performance and distributional impacts. Environment, development and sustainability, 11(3): 549–569. doi:10.1007/s10668-007-9129-9.

[8] Haas, M.; Pichler, C.; Furchtlehner, J.; Heger, N.; Lehner, D. & Lička, L. (2023): Grünraumgerechtigkeit für eine resiliente Stadt. Verlag Arbeiterkammer Wien. Wien.

[9] MA22 (Magistratsabteilung 22) (2015): Urban Heat Islands. Strategieplan Wien. Wien.

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