Thesis document - Jana Milosovicova - Urban Design English

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2.1 Urban heat island (UHI)Only since the 1995 severe heat wave in Chicago, which contributedto a significant number of deaths, particularly among senior citizens,or the 2003 heatwave in central Europe, which had a death toll of tensof thousands of people, has it become clear that the temperature extremesare tightly connected to the urban climatic conditions, and tothe phenomenon of the Urban Heat Island (UHI) (Kropp and Reckien2009, p. 4). The UHI, besides increasing the daily urban temperaturesto the non-conforming extent (and thus causing higher mortality ratesdue to blood circulation collapse), has a severe effect on the abilityof people to rest and to recuperate from heat stress during the nighthours. If the temperature at night is not cooled down to below 25°C,the sleep depth is lowered and the regeneration function of sleep lost(Hahn-Herse 1997, Section ‘Climate’, p. 20). This may cause severehealth problems, and was the main reason for death of thousands,prevailingly elderly, people and people with cardiovascular problemsduring the 2003 European heat wave.The UHI means the difference in the air temperature betweenan urban area and its surrounding natural environment(fig. 6). The main occurrence of this effect is at night,when the surrounding rural environment cools down muchfaster than the city, where the heat stored in the buildingmass and roads is released only slowly into the atmosphere.For example, the temperatures in the centre of Berlinon a clear windless night can reach 9°C higher than itsoutskirts (Urbis Limited 2007, p. 15).As various authors/sources 7 explain, in urban areas, buildingsand paved surfaces have replaced natural landscapes,significantly increasing the rainwater runoff and reducingthe natural cooling effects that shading and water evaporationfrom soil and leaves ordinarily provide. Instead, solarenergy is absorbed into roads, buildings’ walls and rooftops, causingthe surface temperature to become higher than the ambient air temperatures.Meanwhile, tall buildings, closed building blocks and narrowstreets reduce airflow and heat the air trapped between them. Wasteheat from vehicles, industrial plants, buildings (especially from heatingand air conditioners) adds warmth to the surroundings, further exacerbatingthe heating effect. In addition, the urban “greenhouse” effectcontributes with long-wave radiation reflected from polluted urbanatmosphere. These phenomenons, known as “urban heat island”, canraise air temperature in a city by 10°C and even more.Fig. 6 Urban heat island profile (Kravčík et al.2007, p. 28)The UHI augmenting factors are (fig. 7):• Evapotranspiration loss: Reduced green spaces in cities,replaced by sealed materials 8 , lead to more sensible (thermal) heattransfer;7 The Physical Environment; EnvironmentAbout; Kravčík et al. 2007, p. 14-15;Schmidt 2009; Emmanuel 2005, p. 24-25; Sass, online8 Which have a strong three-dimensional structure, and thus have a higher surfaceproportion of man-made materials than the original environment.2 Literature review: The impact of built structures on climate, energy flow and the water cycle13
• Urban geometry: Tall buildings within urban areas provide multiplesurfaces for the reflection and absorption of sunlight, increasing theefficiency with which urban areas are heated – called the urbancanyon effect. Another effect of buildings is the blocking of wind,which also inhibits cooling by heat transport (Wiki UHI, online);• Anthropogenic heat waste coming from vehicular traffic, air-conditioning,electric devices such as computers, refrigerators etc.;• Urban “greenhouse” effect: Long-wave radiation emitted frompolluted urban atmosphere.Matzarakis (2001) stated that it is the thermal characteristics of constructionmaterials (particularly the level of surface sealing) and theeffects of urban geometry that influence the UHI extent in the mostsignificant way (Matzarakis 2001, p. 50-51). Interestingly, the immissions-relatedgreenhouse effect is “relatively unconsiderable” (Matzarakis2001, p. 51), compared to the two above mentioned factors. 9Fig. 7 Causes for UHI (Emmanuel 2005, p.25)Emmanuel (2005) summarized approaches explaining the nature of urbanheat islands, and stated that it is the energy-based approach thatnot only explains the causes, but also points to urban design solutions.According to this summary, the primary energetic effect of urbanization,causing the UHI is “(…) partitioning of more heat into sensible (=thermal heat) rather that latent form (= thermal energy withdrawn inthe process of vaporization of water, not connected with increasing oftemperatures)” (Emmanuel 2005, p. 25). The imperative message thusis to bring more evapotranspirative surfaces back into cities. 10The evapotranspiration of water affects the air humidity, which influencesthe intensity of the UHI. The higher the air humidity, the lowerthe temperature differences between the city and its surrounding naturalenvironment. In the cities with higher air humidity in coastal regionsof mid-latitudes (Park 1987 in Marzluff 2008, p. 241) and in tropicalhumid climates, the intensity of the UHI is much lower (Matzarakis2001, p. 111). The increase in air humidity to tackle high urbantemperatures with the help of evapotranspiration is thereforeessential.A fundamental argument of this Thesis however is that it is both surface/landscapedesign and urban form that have a significant effect oneither increasing the UHI or in reducing it. The way in which we designcities might thus contribute to the alleviation of UHI, maybe even withpositive effects on regional and global climate. Interestingly, even theIPCC Report 2007 only mentions the relevance of the reduction of GHGemissions to mitigate the climate change, but not the direct effect ofland use modification – and thus the changed surface characteristicsand temperatures and options for their mitigation.Fig. 8 Values of solar radiation on a clear day(above) and on a cloudy day (below). Recordedon 18 July 2006 and 3 August 2006, in Třeboň,Czech Republic (Kravčík et al. 2007, p. 24).9 And, since urban design does not offer ways to deal with the emission of pollutantsitself, only on their trapping (with providing ventilation exchange betweenthe pollution sources, such as highways, and compensation areas, such as urbanparks; and with enhancing greenery – all discussed in the next chapters), nodetailed attention will be given to the pollution issue in this Thesis.10 Key terms are highlighted in bold typeface as takeaway for the reader who isinterested in applying the CSUD guidelines to his/her projects.14Climate Sensitive Urban Design in Moderate Climate Zone: Responding to Future Heat Waves. Case Study Berlin Heidestrasse/Europacity
Page 1 and 2: Master’s Thesis in Urban Design:C
Page 3 and 4: ContentsAcknowledgements 5Abstract
Page 5 and 6: 4Climate Sensitive Urban Design in
Page 7 and 8: Abstract Deutsch/GermanAusgehend vo
Page 9 and 10: 8Climate Sensitive Urban Design in
Page 11 and 12: ing population 5 ) - more than a ha
Page 13: as the immense climatic effects of
Page 17 and 18: -°CFig. 11 Photographs of thin veg
Page 19 and 20: Fig. 14 Photograph of the square an
Page 21 and 22: the values of water balance of vari
Page 23 and 24: size, lower than in cities of North
Page 25 and 26: wave radiation towards the sky. In
Page 27 and 28: Impact of the street orientation on
Page 29 and 30: Emergingof fresh andcold air100-200
Page 31 and 32: a. b.On the other hand, a concave w
Page 33 and 34: a.b.-°C-°C50-300 m-°CNot only te
Page 35 and 36: 2.5 Literature review: Lessons lear
Page 37 and 38: 3 Climate-Sensitive Urban Design(CS
Page 39 and 40: ought in the section 3.4, are mainl
Page 41 and 42: 3.2 Proposed CSUD GuidelinesThe set
Page 43 and 44: effect of a water body reaches into
Page 45 and 46: the street);c. Option b) + some of
Page 47 and 48: • Reduce quantity of lanes, where
Page 49 and 50: 3.3 Examples of CSUD in built urban
Page 51 and 52: 3.4 Climate-Sensitive Urban Design
Page 53 and 54: a.The proposal features a number of
Page 55 and 56: Action category ‘Ventilation’Ve
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Page 59 and 60: 4 ConclusionsBased on the need to a
Page 61 and 62: Complementing recommendations regar
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Mitigation “Measures taken to red
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SourcesBibliographyAgenda 21, onlin
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Matzarakis, A. (2001): “Die therm
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The Physical Environment, online:
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Fig. 25 The ‘sky view factor’ .
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Fig. 93Fig. 94Proposed street and c
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Appendices76Climate Sensitive Urban
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Type of landuseDirect impact and ef
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Appendix 2 City of Toronto’s Stud
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(BAF - Biotope Area Factor continue
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The building of the Institute of Ph
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Castello development, seen from Lan
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Bo01 seen from the 56th floor of th
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(Bo01, Malmöcontinued)Water is the
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Appendix 9 Posters Climate-Sensitiv
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Thesis document - Jana Milosovicova - Urban Design English

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