Showing local intensity of the urban heat island effect
Climate change in a growing city
The recent cloudburst events show that combined sewer overflows are not the only problem cities are facing today. In recent years, extreme heatwaves and urban flooding occurred more frequently due to the accelerating changes in climate. According to the world metrology organization, the last four years have been the hottest ever measured. At the same time, storms and extreme rainfalls are becoming more frequent (Bericht der WMO: 2018). In short, hot air absorbs more water than cold air and, when saturated, more rain pours down. The effects of climate change hit urban areas in a particular way. City surfaces are rigorously sealed and thus heat up faster than the surrounding landscape. In particular dark surfaces such as streets and buildings absorb solar radiation during the day and cool languorously at night. This phenomenon is often referred to as ‘urban heat island effect’. Another factor is the lack of green areas that are adequately supplied with water, which cool their surrounding by evaporation and by absorption of the solar energy through photosynthesis. Some structures have opposing effects on the city climate at night than during the day.
Waterbodies, for example, cool their surroundings through evaporation during the day but also store warmth that they emit at night. An opposing example is the huge open fields like “Tempelhofer Feld”, that is the biggest contributor of cold air at night within Berlin, because it has very limited heat storing capacities or buildings around, which can store heat (SenStadtUm 2016). Yet during the day, without wind, such open flat areas can have a radiation temperature of up to 50-degree Celsius (Ehlerding 2016).
The summer of 2018 predicts what can be expected in the future. To be specific; long heatwaves in summer that are especially unpleasant in tightly sealed, urban centres. Not only does overheating cause a decrease in work and learning capability, according to the Tagesspiegel, a combined study by several universities called „city climate and heat stress“ showed that in Berlin around 1600 people annually die prematurely due to heat-related stress. The great European heatwave in August 2003 caused approx. 50.000 heat-related deaths. Paris was one of the cities which was most affected; the mortality rate of people over 75 quadrupled during this period (Ehlerding 2016). The city council reacted fast and developed strategies for climate adaption and cooling in hot periods, emphasizing evaporation and the free use of air-conditioned spaces such as museums. Approaches of a „sponge city“ can already be seen there, like rainwater which is stored on roofs and open spaces, thereby securing the water quality of the river “Seine” and mitigating the heat island effect. Both weather extremes, urban heat and urban flooding, lessen the quality of urban life in the inner cities and therefore urgently need to be addressed in future planning, as urbanization is taking place throughout the world. In the 2050s nearly 70% of all humans will live in cities (United Nations 2014) and Berlin is growing too. The Senate Department for Urban Development and Environment estimates that until 2030, the number of inhabitants will grow by 266.000 (SenStadtUm 2016: 11). Growth, i.e. construction usually goes hand in hand with the covering of more surface area.
Soil sealing 2016 /
Umweltatlas. Showing the
grade of surface sealing in Berlin
„The 21st century is the century of the city and of green spaces within cities. To a great extent, all the important issues facing us in the future, from demographic change to climate adaptation, can be answered through the appropriate treatment of public spaces. As the owners of these spaces, cities, and neighbourhoods, we are responsible for implementing the Strategy for Berlin and achieving significant benefits for an attractive Berlin 2030 with realistic means.“
Reiner Nagel, Board Director Federal Foundation of Baukultur,
offers a summing up prospect for climate change in growing
cities such as Berlin (SenStadtUm 2015: 42-45).
To enable healthy growth, planners, investors, the Senate and neighbourhoods need to take urban climate into account. The Berlin Senate already drew a sustainable picture in their vision for the year 2030, which said that „High-quality growth will have been achieved thanks to Berlin‘s policy of qualified internal development and densification tempered by a sense of proportion that will have limited its consumption of land. [...] Berlin will have succeeded in safeguarding its natural resources sustainably for the long-term, with soil, air and water quality continuing to be vital criteria for developing the city and the health of its inhabitants“. Another point is „sustainable water supply management. Minimizing soil sealing is the yardstick for further development. Water supply, ground, and rainwater management continue to be improved thanks to innovative solutions“(SenStadtUm 2015: 42-45). What can be highlighted from these innovative solutions in the Stadtenwicklungsplan Klima KONKRET from 2016 is, that climate adaption measures are shown to be valuable to future urban planning. How much of it will be implemented or translated into actual laws is debatable.
In an interview with the Tagesspiegel in 2016, Wilhelm-Friedrich Graf zu Lynar, the head of the environmental office in Charlottenburg-Wilmersdorf, argued that solely the building supervision and urban planning authorities are involved in issuing building permits while the environmental and nature conservation authorities, who actually have the know-how to help adapt cities to climate change, are not part of the planning process. The article continues on to state that there is currently only one useful tool for climate adaption, which is the so-called biotope area factor. It stipulates that 60 percent of the total land area of new buildings must be occupied by unsealed areas or green roofs (Ehlerding 2016). But, first of all this law only applies to new buildings and second according to the Senate, buildings only make up 11% of Berlins total area, another 22% are non-build-up sealed areas and “almost 44% of the city‘s surface area is made up of woods, farmland, water, allotments, gardens, parks, and sports grounds“ (SenStadtUm 2015: 42-45). However, those green areas are situated almost in their entirety on the outskirts in places such as Grunewald, the Tegel forest or around Müggelsee. Inner city areas such as Mitte or Kreuzberg-Friedrichshain have the highest degree of impervious coverage, with over 68% in Mitte and 62% in Kreuzberg-Friedrichshain (fig. SenStadtWoh 2016). The 22 % of non-build-up impervious sealed surfaces are mainly streets which are held by the Senate and thus could be directly impacted if so desired.