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Urban heat islands (UHI) have been known since the 19th century (Howard, 1820) and describe the difference in temperature between cities and their rural surroundings. This difference can be up to 12°C (Eliasson, 2000, 31); the phenomenon is caused by the transformation of natural surfaces through e.g. soil sealing, construction of infrastructure and buildings. However, differences in temperature not only occur between cities and their adjacent areas, but also within different parts of cities depending on the provision of green and blue infrastructure as well as on their share of sealed surfaces. The situation is further aggravated by a changing climate. Numerous studies state that the number of heat days (maximum temperature of at least 30°C) as well as the number and duration of heat waves will increase worldwide – especially in cities due to their sealed surfaces, building density and lack of green space (Formayer et al., 2008; Bowler et al., 2010). This problem will become even more crucial in the future: in 2005 approx. half of the world population lived in urban regions and this number is predicted to rise by up to nearly two thirds by 2050 (Schlünzen, 2012). Consequences of those growing cities and expanding urban areas are further densification of settlement areas and loss of open and green space; this strengthens the urban heat islands effect even more. Urban heat islands can have negative effects on human health and wellbeing with sensitive groups such as the elderly being especially affected (Allex et al., 2013).

To counteract UHI and their negative effects, the “Urban Heat Islands Strategy Plan Vienna” has been elaborated as part of a Central Europe project (www.http://eu-uhi.eu/, 2011-2014). The aim was the development of a strategy for the City of Vienna to implement open space planning as well as urban ecology measures to reduce the negative aspects of UHI. Within the project, a guideline has been elaborated by the project team and members of the Environmental Protection Department Vienna (MA 22) to support planners, architects as well as members of the Vienna City Administration, to show possibilities of technical and strategic measures against UHI as well as their potential to reduce urban heat, and to point out planning tools and planning levels. The guideline is available online (https://www.wien.gv.at/umweltschutz/raum/uhi-strategieplan.html, in German).



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