Urban heat island and green infrastructure

Table of Contents

Chapter 1 Introduction

Chapter 2 What is urban heat island?
History
Components of urban heat island
How do urban heat islands form?
City background
Urban morphology
Lack of vegetatìon
Effects
Annual mean temperature
Indoor temperature
Change of city climate

Chapter 3 Mitìgation strategies
Pavement and roof alternatíve materials
Green infrastructure
Green roofs
Green walls
How does green infrastructure work?
Urban vegetatìon
Green roofs and green walls
Green infrastructure in urban canyons

Chapter 4 Copenhagen, Denmark
Denmark background
Copenhagen
Background
Copenhagen transportation
Copenhagen urban heat island - study case
Green infrastructure
Parks and urban vegetatìon
Green roofs and green walls
Indoor temperature
People and Municipality
General public
Architects
Municipality

Chapter 5 New York City, U.S.A
New York City background
Urban heat island in New York City
Mitigation strategies
Urban heat island mitigation programs
Indoor temperature
Green structures
Communities involvement

Chapter 6 New York City vs. Copenhagen
Why New York City and Copenhagen?
Vegetation
Programs
Major urban changes
Ideal Copenhagen and New York City

Chapter 7 Concluding remarks

Acknowledgements

I would like to thank to the people that answered my questionnaires, Københavns Kommune and Teknologisk Institut employees that helped me with information regarding urban heat island in Copenhagen. My appreciation goes to Ebbe Wæhrens, my advisor, who responded promptly to every question and guided me really well into making this report.

Abstract

The theme for the Bachelor report has to be within the construction industry and ŵĂLJ have a connection with the Bachelor Project.

As to every action there is an effect, I have noticed that constructions have a negative impact on urban climate if built in an improper way. The effect is called urban heat island and is not only related to buildings but also to lack of vegetation. As sustainability is a concerning issue in today’s society I have decided to combine somehow the urban climate and construction industry.

Therefore, my aim with this report is to find out the way that green infrastructure influences the urban heat island. Derived from this, there are other purposes for it. I want to find out what is the awareness level among people about this phenomenon and how involved are they in this matter.

My Bachelor Project is a school with flat roof in Ordrup, Copenhagen. Because every new building in Copenhagen with a slope smaller than 30° must have a green roof, this report is also connected to my Bachelor Project.

The first two chapters explain the urban heat island phenomenon and green infrastructure influence on it. Moreover, to reach a relevant conclusion I have decided to make two study cases, one on Copenhagen, Denmark and one on New York City, U.S.A. Each study case contains relevant information about the extent of urban heat island and how efficient is green infrastructure in mitigating it.

The information has been obtained from desk research and questionnaires among architects in Copenhagen, Denmark.

The results of my report show that New York City is very affected by urban heat island, while Copenhagen has a potential for it but it is not yet considered a problem.

I like to think that the most important point from my report is that any form of urban heat island should not be neglected and vegetation will always play a crucial role in a city healthy life.

Glossary

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Chapter 1 Introduction

The 22nd of April 1970 was the first Earth’s Day and at that time, Americans pronounced their concern about the population and cities growth and the exponential increase in the industrial activity. The event spread around the world and the concerned intensified even more when supplies of fossil fuels from the Middle East were restrained and the energy prices increased during the 70’s. That is considered the critical moment when people began searching for ways of protecting the environment. Since then, sustainability and eco-friendly solutions became extremely common subjects in society to prevent climate change and pollution disasters¹.

Climate change refers to any significant change in temperatures, precipitations and wind that lasts for an extended period. On a large scale, there is global warming caused by greenhouse effect and massive deforestation. On a smaller scale, there is urban climate change and this theme will be explained into this report together with its effects and solutions. The urban climate is influenced by a lot of factors, one of them being materials that urban components are made of and their behavior creates urban heat island. This problem has various solutions in different parts of the world but in this case the focus will be on an ancient solution to a new modern problem: green development or green infrastructure in a city represents the answer to the urban climate concern by reintroducing the vegetation that once existed before the settlement. Besides the definition of urban heat island and green infrastructure, the report will treat two study cases on Chapter 4 Copenhagen, Denmark and Chapter 5 New York City, U.S.A. and Chapter 6 is a comparison between them.

Chapter 2 What is urban heat island?

History

“ Did you know that people can affect the environment and even change the weather? Well, next time you are told you cannot, say you already have. ” ²

The more urban areas and construction industry develop, the more profoundly the surrounding landscape is altered but also the city scene is changed. Buildings and streets infrastructure replace open land and vegetation. Regions that were once permeable and moist are converted into impervious and dry surfaces. These changes cause urban regions to become warmer than their suburban areas thus forming heat bubbles in the city. This effect is now known as urban heat island and is absolutely not related to the greenhouse effect or global warming. It is strictly a land use phenomenon, sometimes exacerbated by city activities.

It was in the 1810’s when Luke Howard, a British meteorologist, first investigated and in 1818-1820 described the phenomenon. His study³ was made on the London climate and he documented the effect that built-up areas have on the local weather and temperature. Nowadays, the urban heat island is one of the most studied climate effects of settlements “ and there is now a large body of data on UHI characteristics from cities globally ” ⁴.

Components of urban heat island

In order to identify and describe the urban heat island in one metropolitan area, scientists use temperature registrations of different components. The first component is the surface temperature which represents the temperature of exposed urban surfaces like streets, pavements, façades and roofs. The second component is the atmospheric temperature defined by the air temperature measured in two layers from a vertical city section.

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Figure 2-a Picture illustrates the difference between urban boundary layer and urban canopy layer

These two layers are defined like this:

- Urban canopy layer - represents the city’s layer of air from the ground to the roofs’ level

- Urban boundary layer - represents the city’s layer of air from above the roofs to the point where urban activity no longer influences the atmosphere.

Table 2-a Difference between surface and atmospheric temperatures

Apparently, surface and air temperatures are not related, however surface temperature has an indirect, but extremely significant influence on air temperature, especially in the urban canopy layer. During day time, heat is absorbed by urban infrastructure and edifices and after sunset the energy is slowly released in the air. Consequently, the air temperature in the city during night is maintained at a high level while in suburbs it is cooling down.

Figure 2-b Picture illustrates the city heat bubble

Urban heat island is manifested as heat bubble that incorporates the affected parts of the city. But for a better general understanding, when referred to urban heat island effect, it is normally presented as a temperature difference or comparison between the air within the urban canopy layer and that measured in a suburban or rural area outside the settlement both during day and night.

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Figure 2-c Picture illustrates the temperature difference between the urban and suburban areas

The temperature difference between the two zones is specific for every settlement and it depends significantly on local climate and city morphology. The same rule applies to how warm the urban area is during nighttime compared to daytime. As a general approximation, it could be stated that the city temperature is warmer with 2° to 12°C than suburbs. As a result the annual mean air temperature of a city can be with 1° to 5°C warmer than its surroundings.⁵

How do urban heat islands form?

From the beginning it should be pointed out that every settlement is capable of generating a heat island regardless of its size or location. However, the aspect of urban heat island is characteristic to every city.

In addition to the local climate which is subjected to various meteorological factors such as temperature, relative humidity, precipitations and wind, a number of man-made causes determine the occurrence and intensification of urban heat islands. This phenomenon must be seen as the combined result of energy losses and gains together with the increasing area urbanization.

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Table 2-b Energy losses and energy gains

City background

Climate

Wind and clouds are two of the most significant factors that influence the heat bubble. “ Heat island magnitudes are largest under calm and clear weather conditions ” ⁶ while “ increasing winds mix the air and reduce the ( … ) “ ⁷ phenomenon.

Radiative cooling is “ the process by which a body releases heat ” ⁸. In this case the bodies are buildings and pavements. This process is substantially affected by the presence or absence of clouds therefore the level of urban heat island is different depending on the conditions.

The maximum level of radiative cooling is experienced on cloudless nights. If there is no wind there is nothing that can block the release of heat in the atmosphere. Therefore the air within the urban canopy layer will continuously be heated and in this case the urban heat island reaches the highest point.

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Figure 2-d Picture illustrates how radiative cooling works on cloudy and cloudless nights

Clouds reduce radiative cooling as they increase humidity level and also bring precipitations. Furthermore clouds act like a barrier that absorbs released heat and re-radiate it both back and towards the atmosphere, fact that leads to temperature equalization within the canopy layer.

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Table 2-c Temperature equalization process

When the temperature equalization is reached, the radiative cooling process stops. In this case, the urban heat island is less prominent than during clear sky nights.

Geographic location

Geographic location has also an influence on urban heat island. A coastal city may

experience cooling of urban temperature as well as cities in cold or temperate climates. A city located in the proximity of a forested area has the tendency to create a higher urban heat island than a city developed in a desert. Forests are cooler, therefore the temperature difference between the city and the forest will be higher compared to the desert case where the temperatures could be close.

Urban morphology

An additional factor that influences urban heat island, particularly at night, is urban

morphology. Increasing urbanization heavily alters the ground cover and water. What used to be vegetation, beach or lake, now is converted into a city form which comprises the materials used in every construction, the buildings’ dimensions and spacing and amount of green spaces. Materials’ surface color is also an important factor in the city’s morphology.

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Table 2-d Urban features' effects

Albedo

Albedo is determined by the reflectivity of a surface. It is usually defined as a percentage of reflected radiation or by a number between 0 and 1. An albedo with a value of 1 means that 100% of the incoming radiation is reflected and 0% of it is absorbed. An albedo with a value of 0 means that 100% of the incoming radiation is absorbed and 0% of it is reflected. Additionally, urban geometry influences the wind flow direction and speed.

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Figure 2-e Albedo illustrations

Urban materials

One typical city can have approximately 10-20% of its land surface as rooftops. Concrete, asphalt and pavements may cover up to 35-55% of the city’s area. All previously mentioned surfaces are really burning during summer, and during day time they can be hotter with more than 50°C than the air temperature. These structures and the materials they are composed of have large heat capacity and surface radiative properties that facilitate absorption and storage of solar energy. What is more is that urban construction materials are often dark in color, especially roof coverings and a low albedo effect contributes even more to the development of urban heat island.

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Table 2-e Tall urban canyons

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Table 2-f Low urban canyons

Cities can have multiple and different formations but the ones most relevant to urban heat island are urban canyons. They are like a standard classification of the urban environment, covering the width of the streets and buildings’ height and are usually defined by a ratio between these two factors. Building height is defined by H and canyon width is defined by W, which represents the streets’ width and thus the distance between buildings from the sides of the street. A high ratio of H:W means that the urban canyon is tall and narrow and a low H:W means that the urban canyon is low and wide⁹.

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Figure 2-f Upstream urbanization

“ To cool cities, build them tall and shiny ” ¹⁰. The impression that tall buildings act as a

protection from heat is a completely misplaced one. In fact, small, modern cities with

upstream urbanization can have a larger urban heat island effect than a bigger city with no upstream urbanization.

Figure 2-h When the wind hits a high building, the current divides. A part of it goes up, on top of the building and the rest goes around it. The picture shows that only the upper part of the

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Figure 2-g Shadow effect in high urban canyons urban canopy layer gets ventilated.

This study Thermal Effects of Urban Canyon Structure on the Nocturnal Heat Island:

Numerical Experiment Using a Mesoscale Model Coupled with an Urban Canopy Model ¹¹ on tall and narrow urban canyons demonstrates the complex effect that skyscrapers have. These urban canyons display a larger amount of materials that can retain heat and the façades area is close to or even bigger than the canyon area itself. Buildings act as a barrier against wind and air is hardly circulated. Narrow urban canyons with skyscrapers limit the sky view and streets are most of the time shaded. But even with a modest amount of daylight comes a large retention of heat. At the beginning of the day, only the uppermost part of the façades are directly sunlit, but during the day, the beam of light reaches lower. At the end of the day, more than 60% of the skyscrapers’ façade area is sunlit by the direct light beam and thus results a maximized heat absorption per unit area. The absorbed heat is

released during night and narrow spaces between buildings act as a trap and the cooling

process becomes slower. The amount of released heat combined with hot gas emissions and reduced wind speed make these city segments experience an increased urban heat island effect.

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Figure 2-i Shade effect in low urban canyons

Another very common urban canyon is the wide and high type. Skyscrapers act as wind barriers but there is a higher chance to have a better natural ventilation because of the wide spaces between the buildings. The sky view is larger than in a narrow and high urban canyon therefore the building shading effect is lower. Buildings and pavements receive direct sunlight throughout the entire day and at night the cooling process is slow. This is because a large amount of heat is released in the same time in a relatively small space and there is very little wind to help the process.

Wide and low canyons receive more sunlight and wind enters between buildings easier than in a high urban canyon. Streets are only partly shaded by buildings and buildings across the street rarely shade each other. In this situation, during the day, buildings and streets absorb heat faster and on the entire surface area. Surfaces receive direct light beam with maximum heat and they also absorb the small reflected heat by surrounding materials. Likewise heating process the cooling process at night is also faster because the large space between buildings does not trap the warmth and allows air circulation.

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Figure 2-j Lack of vegetation within a city

Most of the city’s area is covered with different materials which obstruct the growing of vegetation and prevent the ingress of water in the soil. Therefore the natural circulation process of water in atmosphere is completely changed and it becomes a general concern only when it is too late for changing. As a result, city’s top view in general looks like a mass of concrete combined with asphalt and with not too many green spots. Therefore, cities are considered hotspots of heat also due to the lack of grass and trees.

Vegetation provides moisture and shade which helps lower the surface and air temperature. Open land is a living component compared to concrete and asphalt and it is cooler due to water infiltration and high solar reflectivity. When sun is shining the water is released from the ground and it cools the surface and also the air.

Effects

Annual mean temperature

The most obvious effect of urban heat island is that it increases the annual mean temperature of the city.

Indoor temperature

Increased surface heat, especially during summer, can pose a threat to indoor temperatures as well. When a building is designed, façades and roofs are projected to act as an envelope that protects the indoor for outdoor in normal circumstances. But the envelopes’ outside materials are exposed to direct sunlight throughout the day. When the outside surfaces reach abnormal high temperatures hotter than air temperature, the indoor air is affected. As a result, air conditioning and mechanical ventilation systems (HVAC) are overused and the energy consumption of the building is increasing.

Change of city climate

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Figure 2-k Heat bubble effect on clouds

The urban heat island can be represented as a heat bubble which incorporates the city.

“ When a normal cloud hits the heat bubble it can expand up to two times and can blow up about the half way through. This leads to an increase in precipitations and sometimes the midtown can see up to two times more rainfalls quantity than areas surrounding it. ” ¹²

Chapter 3 Mitigation strategies

Even though the urban heat island phenomenon has been substantially studied and documented for a long period of time, communities’ interest and concern regarding the urban climate and its effects is more recent. This increased attention from researchers has facilitated the development of heat reduction strategies but the communities’ informing practice is sometimes insufficient and poorly organized. It is an instinct for everybody to search for a shaded place during summer when in need to cool. As a result, the only solution to mitigate the heat that is known or easiest to remember is vegetation. But in a city is nearly impossible to plant as much vegetation as people would love to have, so even though the focus in this chapter will be on green infrastructure other ways of urban heat island mitigation will be presented too.

Pavement and roof alternative materials

Rooftops are one of the most abundant surfaces in a metropolitan area. Common urban roofing materials include metal, asphalt felt¹³, concrete and clay tiles etc. All of these

materials are impervious and have a very low albedo. Depending on the roof type, different solutions can be taken to reduce the solar heat absorption. The most common one is cool roof which means painting the roof white or other very light colors using special granulated coatings and paintings to increase the light reflectance.

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Figure 3-a Painting the roof white

Streets and pathways cover a substantial area of a city and the materials they are made of are unable to transfer moisture and they also absorb a lot of heat. One solution to solve these issues is cool pavements. All cool pavements have an increased level of permeability but they do not have the same thermal performance. They have different colors, therefore the reflectivity of solar radiation is different.

Green infrastructure

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Figure 3-a Green infrastructure illustration

When referred to infrastructure, people usually mean streets, energy sources and buildings. But there is more to it in a city. Just as networks of streets and buildings are planned, open spaces and vegetation structures can be planed too. This is what green infrastructure means and now is becoming more widely understood to be true. In a city this infrastructure has multiple benefits varying from cleaner air, cleaner water and carbon sinks to a storm water management and heat regulatory infrastructure.

Green infrastructure is about bringing together natural and built environments by using the existing built infrastructure as foundation for new green infrastructure. Therefore green infrastructure means parks and urban forests. Trees are a critical piece of green infrastructure and should not be discounted in favor of other technologies. Constructed wetlands are also a key factor in the green infrastructure as they are the best solution for managing storm water and also beautify parks and help wildlife in urban forests. Lastly, green roofs and green walls bring the benefits of nature closer to the built environment.

Green roofs

“ Green roofs are one of the most exciting developments in sustainable building design ” ¹⁴. Sometimes called vegetated roofs, living roofs or eco roofs they all refer to a system of roofing that uses plants for roof covering instead of traditional roofing materials. Green roofs date to more than thirty years ago, but only in recent years they became promoted and used as an alternative to the traditional roofs. Nowadays green roofs are visually appealing because they offer a larger variety of designs and planting possibilities and they become more and more attractive to homeowners, businesses and even municipalities. Another reason for implementation of this system in cities is due to its environmental benefits while solving a lot of problems.

Structure

Green roofs are every Ɵme constructed in several layers and besides plants, they include growing medium (soil), Įlter fabric, drainage layer, root protĞĐƟon layer, waterproof membrane and insulaƟon on top of the substrate. Nowadays, most of the producers use eco friendly or recycled materials to produce some of the layers in the green roof. The ĐŽŶƐƚƌƵĐƟŽŶ of a green roof as well as types of plants that can be used, depends on various factors such as type of roof (sloped or Ňat), traĸc (no traĸĐ, pedestrians, bicycles) and roof size. Both slopped and ŇĂt roofs are suitable for green roofs but establishing gardens or park like roof systems is limited or completely not allowed to higher buildings as growing large plants and trees is too heavy and risky.

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Table 3-a Table contains a cross-section from each type of green roof

Depending on the plant selection, green roofs can be of three main types: intensive, semi- intensive and extensive. Intensive green roofs have a significantly big layer of growing medium as they are designed to accommodate trees and large plants and they are also suitable for light bicycle traffic. Semi-intensive green roof requires a smaller layer of growing medium and it is covered with plants of medium sizes. Extensive green roof is the most common green roof because it requires a thin layer of growing medium and the covering plants are moss and sedum.

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Figure 3-Ŷ Modular green roof appearance

Some of the green roof systems use pre-planted boxes. This type of green roof is called

modular green roof system and the pre-planted boxes are usually recycled plastic trays with different dimensions. However, in this case growing medium depth is limited for safety reasons and the most used trays are 10 to 20cm deep. This modular system has also been used for large plants such as bushes or small trees, but the trays dimensions and growing medium depth is specifically calculated for each case. The building procedure is very simple as the grid of trays is designed to cover the roof’s surface. Roof structure has to be waterproofed, on top of the waterproof membrane a water drainage layer is placed and then the plants modules are positioned. This option provides mobility and easier maintenance and the exact same benefits as a built-in green roof.

Green walls

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Figure 3-o Green wall

Living walls and green façades are both green walls systems. Living walls are the vertical

version of green roofs, both having similar structures. Green façades are a more simple way to benefit from plants. A green façade uses climbing plants to provide green coverage over a wall.

Green façades

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Figure 3-Ɖ Green façade example

One way to achieve green façades is by using a steel trellis system to hold the vines of plants that are rooted in the ground. Another way to achieve it is to plant ivy or other similar plants next to the façade and let the nature do its work. In this case brick walls provide a better support for plants than concrete walls do. Bricks absorb more water than concrete and usually have a rougher surface, facts that create a favorable surface for plants to grow on.

Living wall

Figure 3-Ƌ Living wall example

Living walls have a larger variety of designs and plants and are more attractive, whereas green façade design is limited to the trellis organization or how plants grow on the façade and a only few plants species can be used. However the benefit is the same.

Living walls are constructed on the façades and they need to be waterproofed either by a gap between the system and the wall or by using a waterproof membrane. In both cases, a layer of root proof material¹⁵ is mounted between the green wall and the wall to prevent plants roots to grow into the façade. Living walls are formed by pre-planted boxes made out

of plastic or metal mounted in a metal or wood structure fastened to the façade. Living walls can support any type of medium size plants species to moss and sedum and the growing medium thickness is given by the types of plants that the wall is intended for. Compared to green roofs, living walls need a special irrigating system that is particularly designed for each wall and it functions like a waterfall. They also need a good drainage system on the bottom.

How does green infrastructure work?

“ Plants are nature ’ s geniuses at staying cool in sunlight and they can do it like no other living thing probably can. ( … ) They are really optimized to thermally regulate ( … ) ” ¹⁶ and this section focuses on the explanation of how they work.

Trees and other landscaping plants absorb water through their roots and in presence of heat they evaporate water in the atmosphere through a process called transpiration. Water evaporation also occurs from the surfaces of vegetation and the surrounding soil. Together, evaporation and transpiration are referred to as evapotranspiration. Heat intensifies this process, therefore the elevated temperatures in the cities create good conditions for plants and the moisture they provide helps cooling the surroundings.

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Figure 3-ƌ Tree shade

Shade is one of the most important benefits that trees can provide. Tree crowns decrease the amount of sunlight that can reach the ground, therefore decrease the temperatures. Their placement at the side of buildings, significantly decrease façades surface temperatures. In a city, the rougher and denser vegetation combined with irregular surfaces of buildings generate turbulence and this removes heat from the surface to the atmosphere.¹⁷

Urban vegetation

Vegetation in a metropolitan area in Europe and U.S.A. usually covers between 14 and 30% of the specified area. The most common open spaces downtown are small squares or medium sized parks, both with limited grass area and sometimes insufficient trees. Trees are most commonly seen in metropolitan areas on tree-lined streets, but city centers rarely see these formations because of high need of traffic space. Most of the metropolitan areas have urban forests in suburbs and these are the areas that increase the percentage of vegetation. But this fact does more damage than good to a city because it increases urban heat island. Therefore is extremely important that trees and parks are equally distributed across the metropolitan area. ¹⁸

Urban trees and parks

The surface temperature within an urban, partly forested park may be 15° to 20°C lower than that of the surrounding area which leads to 2° to 10°C cooler air temperature. The cooling effect extends to the surrounding area and with a size of 0.6km2, an urban park can reduce air temperature by up to 1.5°C at 1km distance.¹⁹

Urban areas can sometimes be a relatively hostile environment for trees due to high

impervious cover, lack of rooting space, soil, water and air pollutants and vandalism. In these conditions their properties and benefits will be reduced compared to urban forests. Nevertheless trees in a city can be responsible for shade, can reduce storm water runoff and improve air quality and they should still be considered as a way of mitigation for a lot of problems.

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Figure 3-Ɛ Tree spacing

For a maximum result, tree spacing should create a continuous awning effect between street ways and pathway. By providing shade, one tree with a large crown in downtown can substantially reduce pavements and façades temperature with approximately 10° to 20°C. On average trees can reduce urban air temperature with about 0.3° to 5°C. Moreover,

according to this report Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas ²⁰, tree shading on buildings have a positive effect also on the indoor temperature. Depending on the façade material, glass, concrete, bricks etc. trees have enough power to reduce the indoor temperature with about 0.7°C to maximum 5.5°C²¹. Additionally, one single tree can reduce more than 130kg of CO2 from the atmosphere yearly²², fact that leads also to a cleaner air not only cooler.

Green roofs and green walls

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Figure 3-ƚ Green roofs and green walls illustration

Several researches carried out by Tyndall Centre for Climate Change show that city centers need at least 10 to 20% more green areas. Moreover Natural England²³ suggests that an accessible natural green space should be no more than 300m from where anyone lives. But buildings and streets infrastructure in a city do not always create proper conditions for parks, for green areas and for gardens because the space is already extremely limited for pedestrians and traffic. Stuart Gaffin, a research scientist at Columbia University, says that the most obvious advantage of these two living structures “ is that they don't take up valuable ground - level space. Roof space is just this wasted resource ”.²⁴

Reduction effect of green roofs and green walls on surface and air temperatures Green roofs and green walls provide the best possibility to create the suburbs’ vegetation in a city, therefore establish a closer temperature between the two zones. Roofs and façades have a significantly big area in a modern city, therefore green roofs and green walls systems are the best solutions to use existing buildings’ surfaces for creating open spaces and as a result establish a cooler and cleaner atmosphere in the city.

Green roofs and living walls create a cover on the buildings that protects them from absorbing heat. These structures reduce surface temperature by the effect of shading but in the same time they help cool down the atmosphere through the evapotranspiration process of growing medium and plants, almost like an outdoor air - conditioning system. Although these structures are recognized as having an important role in mitigating urban heat island, only strategic placement and planning will help improve urban canopy layer air quality and not only in specific spots.

This report Air temperature regulation by urban trees and green infrastructure ²⁵ suggests that a 100m2 green roof or living wall can cool up to a distance of 300m. Therefore, in ideal conditions, the distance between them has to be relatively small, approximately 600m to maximum 700m. But cities never provide ideal conditions and for that reason a distance of 1km to maximum 1.5km is achievable. This long distance is stated because usually buildings have surface areas bigger than 100m2 or the cumulated area from a few, very close buildings is more than 100m2.

Stuart Gaffin and his research team at Columbia University conducted several experiments comparing temperatures between green roofs and normal black roofs. His results showed that while conventional roofs can reach temperatures up to 50°C hotter that air temperature, green roofs surface temperatures remained below and occasionally close to air temperature.²⁶ Because of this, green roofs can reduce air temperature with up to 5°C.

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Figure 3-Ƶ Living walls and green façade comparison

Living walls in a city can reduce the surface temperatures with 10° to 50°C and air temperature with 3° to 4°C, as mentioned in Energy Savings and LEED® Credits²⁷ sections. According to these statistics, green roofs and living walls have the same effect on air temperature in a city. Green façades are not as efficient as living walls, but they provide an irregular surface to façades and thus they produce turbulence. According to this study green façades can reduce air temperature by 1° to maximum 2°C but the effect is not as extended and prolonged as for living walls. They also reduce surface temperature, but their cooling control is limited to a reduction effect of 3° to maximum 11°C.

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Table 3-ď Comparison between living walls, green façades²⁸ and green roofs Albedo

Green roofs and green walls are considered to have an albedo effect because plants have the ability to reflect light. Their actual albedo value is definitely not as high as for a white roof. Depending on the plants that are used the albedo of a green structure can vary between 0.25 and 0.3, which is higher than the value of a black tar roof which normally is between 0.08 and 0.18. The albedo of a white roof is approximately 0.65-0.7, however researches indicate that green structures have a stronger effect on temperatures than white roofs and taking into account the evaporative cooling of plants, generally, the albedo effect of a roof is considered to be 0.7 to 0.85.²⁹

Indoor temperature

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Figure 3-ǀ Comparison between a normal building and a building covered with green roof and living wall

Green roofs and living walls have also a significant potential to regulate indoor temperature which is affected by urban heat island. These structures provide additional insulation to the

building envelope and under no circumstances should they be considered as a replacement for insulation. Their thermal performance is highly dependent on climate conditions and growing medium thickness. An exact constant U-value of the entire green structure cannot be calculated, because these systems are designed to retain water and the thermal properties are reduced with the increasing water content. However what is considered as the most insulating layer in the green roof and living wall structures is the growing medium. When dry or with a minimum water content, it typically has a ʄ (lambda) value of 0.2 up to 6W/m*K, depending on the manufacturer and composition.

According to this study The green building envelope Vertical greening ³⁰ , a green façade

vegetation layer can have an R-value of 0.3 to 2.9m2*K/W and improve the insulating value of a façade with maximum 15%.

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Figure 3-w Comparison between living wall and green façade on impact on indoor temperature

The benefits of green structures, such as the lowering of indoor temperatures and improved air quality have been indicated in several studies. According to this study The Role of Extensive Green Roofs in Sustainable Development ³¹, because green roofs and living walls have good insulation properties, they have the potential to reduce indoor temperatures with 3 to 5°C on a day with outdoor temperatures between 25 and 30°C. Moreover, according to this study Federal energy management program - Green roofs ³², ventilation units installed on green roofs are able to operate less intensively and at higher efficiency due to cleaner air.

Compared to a green roof, a cool roof is not as efficient but still has the potential to cool the indoor air temperature with maximum 2°C.

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Table 3-c Comparison between living walls³³, green façades³⁴ and green roofs Variety of usage

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Figure 3-dž Green roof garden

Green roofs and living walls are not only advantageous and beneficial for urban and indoor temperatures but they are also practical. They provide a large variety of usage methods and the most common ones are gardens for growing flowers, fruits and vegetables. In order to maintain gardens, they need irrigation and these two green structures are very good at providing water because they are solutions to storm water management. Green roofs and living walls can retain 40% to 80% rainfall water in the growing medium and drainage layer. The surplus amount of water can be filtered and used for irrigation of these two structures to maintain them at the highest capacity.

Green infrastructure in urban canyons

Urban canyons have one thing in common: they sometimes represent the urban core and therefore from the pedestrians and traffic point of view, these are the most crowded areas in a city. Urban canyons mitigation strategies are usually the same, but everything depends on the free space between buildings and streets.

High urban canyons

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Figure 3-v High urban canyon space between buildings

In high urban canyons formations, heat is extremely challenging when it comes to mitigation strategies. Buildings are very tall and are designed to accommodate a large number of people. Streets and pathways need to take a very heavy traffic every day and usually the biggest priority in these areas is how to create more space for pedestrians, bicycles and cars. As a result, the concrete and asphalt surfaces areas are increasing and so does the air temperature. Free spaces between buildings or between pathways and streets are limited or sometimes inexistent, therefore creation of green areas on the ground level is an interesting challenge.

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Figure 3-z High urban canyon green roofs and living walls

Some municipalities have decided to transform the streets with the heaviest traffic within the high urban canyon into zones opened only for pedestrians. As a result there is enough space to create vegetation areas with trees to create shade on pavements and buildings. One example is New York City, Manhattan. In other cases, this method for creating open spaces is nearly impossible or unwanted, therefore other means to fight the heat have to be used. In these circumstances, green roofs and green walls can be the solutions. They have to be used combined because there is a big distance from the ground to the roof tops. If only green roofs are used, only the upper part of the urban canopy layer will be cooled down. Even though cod air is heavier than warm air, there is very little or inexistent vertical air circulation to facilitate the cooling process at the ground level. Therefore, at the base level of urban canopy layer, green walls systems have to be implemented to achieve the best results.

This report Experimental study of the urban microclimate mitigation potential of green roofs and green walls in street canyons ³⁵ shows that in high urban canyons the use of a white paint on façades facing streets can reduce the air temperature within the urban canopy layer with about 1.5°C. But the living walls used in combination with green roofs can reduce the air temperature with approximately 10°C. This proves how efficient plants can be in such a demanding environment. Green roofs and green walls also increase the humidity level inside the urban canopy layer.

Low urban canyons

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Figure 3-aa Low urban canyon air circulation between green roofs and living walls

Low urban canyons are the most common city formation. Heat in low urban canyons is not as difficult to mitigate as it is in high urban canyons. Even though all the surfaces are constantly exposed to direct sunlight, wind or slow turbulences will always be present during both day and night. In this kind of city formations, air within the urban canopy layer gets ventilated. Vertical turbulences between buildings triggered by wind will rise up faster the hot air within the urban canopy layer and this will be mixed with cooler air within urban boundary layer. This air flow advantages the cooling process at night but at some extents also regulates the air temperature during the day. In low urban canyons, trees are very efficient because buildings have a low height and most of their façades area can be shaded. Trees can also reduce the amount of sunlight that hits the pavements’ surfaces and therefore they help cool down the surface temperatures much easier and faster than in a high urban canyon.

Ground to roof connection

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Figure 3-bb Ground to roof connection method

Previously, green roofs and green walls have been treated as individual elements with their individual properties and benefits or without a structural connection. Creating a connection between the green roofs and ground with the help of living walls creates additional opportunities and increases the benefits to the buildings and also to the surrounding environment. In low urban canyons green roofs and living walls can be used alone and they will have a positive and noticeable effect on the city climate due to the vertical turbulences and also on indoor temperatures. However, this type of urban canyon provides the best profile for a ground to roof connection. Usually there is more space for vegetation, small parks or gardens on the ground and the advantageous low height of buildings provides the best opportunity to extend the existing or newly created green spaces by forming a ground to roof connection³⁶.

Chapter 4 Copenhagen, Denmark

Denmark background

Denmark has a generally temperate climate. It has mild winters and cool summers and is usually referred to as a windy country. The low average temperatures are largely conditioned by the generally westerly winds and by seas. Rain is another characteristic feature of Denmark. Rainy days are likely all year round, but second part of summer and autumn are the wettest seasons while spring has the least amount of precipitations.³⁷

Creating a green and sustainable society is one of the key goals for Denmark, therefore it is one of the best countries at promoting and implementing environmentally friendly and sustainable solutions in all sectors³⁸. The past years have been significantly marked by huge concerns for municipalities and climate specialists regarding climate change and how cities are affected by it. As a result, a significant number of climate adaption plans have been made to solve different issues.

Copenhagen

Background

Copenhagen is the largest and the most populated city in Denmark. The city has an area of 86.20 km2 and the metropolitan area is extended up to 2778.3km 2. City population density is 6600/km 2 and metropolitan density is 702/km 2.

From the geographical point of view, Copenhagen is located on the eastern shore of the island Sjællands. Increasing urbanization has altered natural landscape, both the ground and water with minor land reclamation³⁹. Copenhagen climate is highly influenced by the sea and also by the westerly winds. The average temperature in winter is 1.6°C and in summer is 17.3°C. Rain falls are frequent throughout the year and the annual precipitations average amounts to approximately 220mm.

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Table 4-a These tables illustrate the climate within the last ten years in Copenhagen⁴⁰

Copenhagen is the best city that demonstrates Denmark’s intentions and actions. The most important report that summarizes them is Copenhagen climate adaption plan⁴¹ . This report takes into consideration all factors that influence Copenhagen’s climate and provides methods of dealing with all the problems that the city has in order to make it Carbon neutral by 2025. On the other hand, according to my questionnaires’ results and desk research, Copenhagen, out of all big cities in Denmark, is the most predisposed area to produce urban heat island.

Copenhagen transportation

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Figure 4-a Copenhagen mean of transportation

Copenhagen has always been considered as a green city when it comes to transportation, however since the implementation of Copenhagen climate adaption plan in 2011, various measures have been taken with regards to bicycle traffic. Transportation method in Copenhagen lowers the possibility of abnormal heat in the city because more than 52% of all Copenhageners cycle. This percentage corresponds to 5.2 bicycles for each car and the number of people that choose bikes over cars is increasing with every year. Even though more than half of the Copenhagen population chooses a green mean of transportation, only 5% made this decision because of the environment.⁴²

Copenhagen urban heat island - study case

The most likely areas and neighborhoods where amplified heat can be felt are København K, Vesterbro, Nørreport, parts of Sydhavn, Amagerbro and Nørrebro. City’s general morphology can be described as a low urban canyon because buildings’ average height is about 15m and the previously mentioned neighborhoods make no exception. Most of the buildings in these areas are built with brick façades and roofs are typically covered with dark roof tiles or asphalt felt. The period in which these areas are most likely to create a heat bubble is only during summer when air temperature reaches more than 25°C. These temperatures are considered heat waves in Copenhagen and they can be intensified by traffic during rush hours. These neighborhoods are the most crowded during rush hours and this could be one of the reasons for higher temperatures compared to other areas. Moreover, being a low urban canyon with rather wide streets, besides rooftops, façades and pavements also absorb heat from direct light beam the entire day.

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Figure 4-b The maps show the maximum surface temperatures on the 2nd of June 2006, 18th of June 2006, 20th of July 2006, 22nd of September 2006

In the Copenhagen climate adaption plan is a study made on the surface temperatures of the city and the formation of heat bubbles in June, July and September, all in 2006.⁴³ The maps indicate that there are relatively big differences in the surface temperatures between the city and the suburban areas. The coldest areas are water surfaces, inner parks and surrounding forests. On the hottest day, the 20th of July, surface temperatures reached up to 47°C while the surface temperatures in the other days were between 32°C and 44°C. The maps also show that the surface temperatures within the city depend on how densely built- up are the areas. Midtown is one of the most affected areas in all four days while open residential areas are affected much less. Although vegetation can have a cooling effect, the maps show that the areas densely covered with trees have a lower surface temperature than grass open lands. The reason could be because grass has a superficial root system and if it is not irrigated properly, it dries out fast.

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Table 4-b This chart shows the average surface temperature differences between five different urbanized zones in Copenhagen area in the four chosen days.

The biggest variations are seen between industrial areas and forests where the difference is more than 10°C. There are also differences between densely built-up areas and sparsely built up areas, but the differences are smaller. It should be noted that the greenery areas within the city are the coolest ones. Finally, it is interesting to note that the temperatures differences between densely built-up areas and sparsely built-up areas are very close to the differences between sparsely built-up areas and greenery.

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Table 4-c In order to have a better understanding of the data in the maps, this table shows a comparison between the air temperature and surface temperatures during daytime in the specific four days.

It is interesting to note that the difference between the two target temperatures reached 19°C on the 20th of July.

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Table 4-d This chart shows the temperature diīĞrence between day and night in the speciĮc four chosen days.

It should be noted that the air temperature during night is ůŽwer than the temperature during day. This prŽves that the heat bubbles fŽrmed during the day are easily dissipated at night.

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Table 4-e These two charts contain informaƟon about the wind speed and humidity in these 4 days.

It is interesting to note that on the windiest and most humid day out of these four days, 22nd of September, the difference between day and night air temperatures was of 5°C and the difference between air and surface temperature during day was of 13°C.

Throughout the year, on average, the temperature difference between city and suburban areas is 0.5° to 1.5°C, which is almost insignificant. But during summer heatwaves, there can be a temperature difference of 3° to maximum 10°C between downtown and surrounding areas. Though, the biggest differences, close to 10°C, can be reached only between the temperature measured downtown and that measured in surrounding forests. But as previously mentioned, weather plays an important role in the cooling process at night.

Copenhagen has a windy climate and at night the surface temperatures get very fast cooled down and as a result the air temperature difference between midtown and suburbs is not extremely prolonged.⁴⁴

According to the Copenhagen climate adaption plan and information presented before, urban heat island in Copenhagen is not considered as a threat. Generally windy and rainy weather keeps the temperatures down and the heat bubbles that form in the city are very easily dissipated. Moreover, Copenhagen hardly ever presented continuous heat waves when temperatures exceed 25°-28°C.

On the other hand, also according to Copenhagen climate adaption plan, specialists are aware of urban heat island effects in other world’s big cities. Annual average temperature in Denmark is increasing “ and the prospect of a greater number and more intense heat waves may pose special challenges ” ⁴⁵ in the city. Even though urban heat island is not a challenge yet in Copenhagen, still the city is expanding and during these heat waves it has a potential to create heat bubbles. Therefore Copenhagen climate adaption plan presentation of urban heat island had as purpose making general public and construction industry aware of its possible impact. Additionally, Copenhagen’s target is to be carbon neutral by 2025 and this phenomenon may have a negative influence on the plan, therefore the report also contains methods of preventing it.⁴⁶

Green infrastructure

Copenhagen is considered a green city, not only because of the sustainable programs implemented to solve different issues, but also because of the vegetation spaces that that cover a significant part of the metropolitan area. The picture below shows that Copenhagen is surrounded by several suburban forests and also has an important number of parks within the city.

Parks and urban vegetation

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Figure 4-c Copenhagen satellite view

Parks in Copenhagen are historically formed and most of them are the biggest ones in the city. Currently, vegetation area in Copenhagen occupies more than 25% and the plan is to increase it with pocket parks⁴⁷, city gardens, trees and vegetation on most of the streets, green roofs and green walls. The goal is that more than 90% of people living in Copenhagen can reach a park or a natural area within fifteen minutes of walking. Therefore, pocket parks area relatively easy to fit in and 14 of them have already been created. Moreover 3000 street trees have been planted and the number of city gardens is increasing.⁴⁸

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Figure 4-d This map shows the location of pocket parks

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Figure 4-e This map demonstrates that there is a significant number oĨ parks and vegetated areas within the city and that the goal of a short walking distance to any of them is very easy to achieve.

Green roofs and green walls

Copenhagen has already a multitude of parks but it is necessary to create more vegetation areas. However, land open spaces are limited and in order to achieve the goals it makes sense to utilize any existing free space to turn it into a green area. Green roofs and green walls do not require extra space as they are an upgrade of an existing unused area. Like any other city, Copenhagen has a big area of roofs and façades that could be used to extend the greenery. Green roofs in Copenhagen have always been considered as a modern and climate friendly solution and an important part of the Copenhagen climate adaption plan contains information about them. The target imposed by the plan in 2011 was to have 150000m2 more of green roofs in Copenhagen before 2015. A statistic provided by Dorthe Rømø from Copenhagen Municipality in one of her publications⁴⁹, presents the current status and the potential of green roofs for the next years in Copenhagen:

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Table 4-f This statistic proves that the target has been achieved this year and is expected to increase in the next years.

Living walls in Copenhagen are not very popular as outside structures because of the weather. Strong winds may destroy the structures, therefore not too many people choose them for large areas. Living walls are more used inside for a better indoor climate. Green façades are more common because they do not require too much maintenance and sometimes they appear unintended. According to this source, there are more than forty big green façades in the city center area and one of the biggest ones is at Vesterport.⁵⁰

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Figure 4-f This map shows the flood risk in Copenhagen and therefore is representative for the impermeable materials that cover the city

“ A greener Copenhagen, is a climate - proof Copenhagen ” ⁵¹. The green solutions in this respect are associated with the use of water, shade, air circulation, vegetation and high

surface albedo and permeability. According to the European Environment Agency about 60% of the Copenhagen area is covered with impermeable materials and severe rain falls cause a lot of critical problems in the city⁵². Therefore all these green areas that form the green infrastructure in Copenhagen, are solutions to storm water management and have as main purpose diminishing the pressure on the sewage system. The fact that the green infrastructure of Copenhagen helps reduce the temperatures during heat waves is a plus. According to Københavns Kommune, the tests of how much green roofs and green façades reduce the air temperature in Copenhagen are still on an experimental level but they are not less efficient than in other countries.

When it comes to parks, according to⁵³, Fælledparken effect in Copenhagen of reducing the temperature during heat waves can be measured up to 100m away from the park.

Indoor temperature

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Figure 4-g Indoor temperature

Indoor temperature in buildings in Copenhagen is another subject treated by a number of plans and regulation documents. Buildings Regulations 2010⁵⁴ state that all structures have to be very well insulated in order to avoid heat loss. Good insulation prevents the heat transfer from the exterior wall layer to the interior one, therefore, indoor overheating in Copenhagen is not a serious problem during heat waves when surface temperatures can be elevated. Even so, there are some companies and regular people that install indoor living walls or gather many plants inside for a better indoor climate. Green roofs provide additional insulation and they are most of the times used also to achieve the required U- value for roofs⁵⁵.

People and Municipality

General public

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Figure 4-h Copenhagen summer

According to my research results and experience, people are aware of the fact that average temperatures are increasing and heat waves are not specific for Denmark. However, people are really happy in the summer and they try to enjoy sun and warmth as much as possible every time they have the occasion.

General public interest in green walls and green roofs is growing because of the various opportunities that they offer. Block residents would love to create more attractive courtyards with a lot of vegetation. There is an interest to explore more solutions, such as green walls to extend the vegetation from the ground thus creating more space for growing fruits, vegetables and flowers. In addition to the green courtyards, there is a great interest in installing green roofs as well for the same reasons. Although the majority of people would love to expand the green areas on the blocks and around them, there still are a few skeptical people about green structures. Green structures are ruled by the municipality to be integrated with storm water management systems and all together require maintenance. Even though residents strong desire for more common green spaces, they affirm that the maintenance and care that these structures require could overwhelm them. As a result, municipality and architects have some issues when it comes to green structures implementation. On the other hand, when it comes to a green wall or green roof installed in the private space, indoors or on the terrace, people are more open.⁵⁶

Architects

Most of the architects questioned affirm that they are aware of a certain temperature difference between Copenhagen city center and suburban areas because of the multitude of forests that surround the city. However not all of them know that this is called urban heat island and they do not consider it a threat. All of them said that they do not take into consideration surface temperatures when they choose the façades cladding or roofing materials, because these are most of the times decided by the client or are already restricted in the local plans.

Anja Pelle, Projektsalg - grønne tage from Byggros⁵⁷ said that the company is aware of the Copenhagen’s potential for creating urban heat island and that they are trying to collaborate with as many architects as possible to contribute to the development of the green areas. And what regards their intention, it could be called a success because they have doubled their turnover from 2011 to 2012.

Municipality

In 2010, the Technical and Environmental Committee decided that all new buildings in Copenhagen with roof slopes smaller than 30° must have green roofs. Moreover, the municipality of Copenhagen wants to use these green roofs to create a continuous green network in the city. In the Copenhagen climate adaption plan, there is a table with recommendations regarding this initiative:

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Table 4-g Copenhagen climate adaption plan planning⁵⁸

Chapter 5 New York City, U.S.A.

New York City background

City of New York is the most heavily populated city in the United States. From the geographical point of view, it is located in a coastal area at the mouth of Hudson River into the Atlantic Ocean. The city’s territory has been extensively altered by human intervention, especially with considerable land reclamation. At the present time the city total area is 1214km 2 , 790km 2 out of it being land and is increasing with every year. New York City’s land use is characterized as a highly developed urban core on Manhattan Island and a sprawling dense suburban area. The average building height in the city is approximately 142m.

The city’s climate is influenced by the Atlantic Ocean and has 2.5°C as average temperature in winter and 24.9°C as average temperature in summer. Hurricanes and tropical storms are rare in New York, however they are not uncommon.

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Table 5-a These tables illustrate the climate within the last ten years in New York City⁵⁹

Urban heat island in New York City

In the city of New York, urban heat island is a very well - known fact and it causes a lot of problems in various parts of the city, especially in the areas with high buildings. In the last two decades there have been countless researches and analysis made by different scientists and city government regarding atypical increased heat in some urban districts. In the last years, abnormal city climate became a bigger concern also for general public and the number of local communities involving in various heat mitigation programs is increasing.

One of the most problematic zones regarding urban heat island is Manhattan. This district has the shape of a high urban canyon with buildings height ranging from around 70m up to 541m but the average height is of approximately 130m. The traffic in this area is overwhelming and combined with the large amount of materials that can absorb heat during the day, Manhattan is considered the hotspot of high temperatures in New York City. However, during the day there are multiple regions with higher temperatures than in Manhattan. But then again during the night, the temperature remains elevated in this specific region while in the other areas, the cooling process happens much faster and considerably easier.

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Figure 5-a Manhattan map

During summer temperatures are elevated and in this period urban heat island is more accentuated. Summer temperatures in the city are in average 4°C warmer than surrounding suburban and rural areas. During winter city temperatures are in average 3°C warmer than surroundings.⁶⁰ According to this research Variations in New York city ’ s urban heat island strength over time and space⁶¹ in New York City, on a typical summer day with 30°C air temperature, roofs and upper parts of buildings’ façades can reach more than 80°C, while the pavements and streets on the floor of the urban canyon have a temperature varying from 65° to 80°C.

Mitigation strategies

Urban heat island mitigation programs

Absence of parks, gardens and street trees is a well-known problem in New York City districts and in 1996 the first program with the intention of greening the city has begun. It is called the Greenstreets and the purpose is to “ change unused road areas into green spaces that beautify neighborhoods, improve air quality, reduce air temperatures ( … ). Since its beginning, over 2500 Greenstreets have been built citywide ” ⁶² and the below table shows the current status.

Figure 5-b This table shows the percentages of vegetation and impervious surfaces in some of the New York City neighborhoods. The percentages are comparative to the specific zone.

Landscape architects work together with the city government and local community groups to determine how best to increase the green infrastructure in the city. In Manhattan, more than half of the buildings’ roofs and terraces are no longer impervious because of the multitude of programs implemented by the government to fight the heat.

The most important plan is called PlaNYC 2030⁶³ and it was implemented in 2007. Since then 903000 trees have been planted and in 2014 New York City had the cleanest air in the last 50 years. Moreover, since September 2013, an additional 185000m2 of black asphalt felt roofs have been upgraded to green roofs. Currently only 14% of the city area is covered by parks and gardens and they help reduce the heat, but the program is continuing. According to NASA “ about 14 percent of the New York City ’ s impervious surface area consists of rooftops, most of them dark, heat - generating surfaces, typically tar ” ⁶⁴. If this all this area is to be transformed into green roofs, then the percentage of gardens could grow up to 28%.

In January 2010, one major project called Green light for Midtown⁶⁵ has been implemented in the midtown area, Manhattan. The idea was developed as a little part of the PlaNYC 2030.

This project was a “ major initiative in the City ’ s efforts to improve mobility and safety ” ⁶⁶.

However it also had a smaller and not that important objective to increase the green areas in midtown and have lighter colored streets and pathways. Some trees have been planted but more have been placed in large pots to ensure flexibility. Most of the streets have been temporarily painted in green and blue colors. The project was a success at that time as the lighter surface colors ensured a lower temperature for pedestrians.

Another program called NYC ° Cool Roofs⁶⁷ (White roof project)⁶⁸ , has as purpose turning most of black asphalt felt roofs in New York City into white roofs. The procedure is by painting the roof covering with a highly reflective paint, of minimum 0.75 albedo as stated in the project law⁶⁹. According to the White Roof Project research on a summer day with 32°C a white roof surface temperature is with 6°C warmer than the air temperature and with 44°C cooler than a black asphalt felt roof⁷⁰. Since the project started in 2010, more than 535000m 2 of roofs have been painted white in New York City metropolitan area⁷¹.

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Figure 5-c Map of New York City with white roofs at the end of 2012

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Figure 5-d White Roof Project research

Even though white roofs are more used than green roofs, the latter have greater heat mitigation potential. In Manhattan, while a white roof has the power to cool the air temperature with 0.7°C on a summer day, the same area of green roof can cool the air around with approximately 3°C and the effect is extended on a larger area.⁷²

Indoor temperature

New York City has to struggle every summer with air conditioning and mechanical ventilation of every building. Because of the intense heat and the amount of units running in the same time, long power blackouts are very common and people had to find solutions to improve the air quality indoor. A lot of companies took the decision to install living walls indoors because of design reasons, but in time they realized the positive effects that they have on indoor climate. As a result, this solution became with time popular and more people and companies take the decision to install a living wall inside to help the air conditioning. Indoor temperatures during summer are very close to the outside temperatures and a living wall indoor can reduce the room temperature with as much as 7°C.

Green structures

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Figure 5-e The Trump Tower in New York City - trees are planted on buildings terraces at different levels

Green façades and living walls are a common choice between New Yorkers but not as common as green roofs. Living walls are mostly used inside or on terraces and balconies.

Green façades are also an appealing design in New York City and they appear mostly on old buildings. On new buildings, a full or partial green façade is achieved by plants that people grow in their balconies or hanging from the outside window sill.

Green roofs are increasing not only because of the multitude of promoting programs and laws but also because people discovered the benefits that these structures have. Most of them are becoming used as fruits and vegetable gardens, especially on the apartment blocks, schools and kindergartens. Moreover a nice flower garden on each apartment terrace increases the property value. Therefore the real-estate agencies are taking advantage of this feature and implement green roofs and green walls in more and more buildings. As a conclusion, most of the people’s reasons for adding a green roof or living wall anywhere in the city are more oriented to economic benefits or attractive view and practical usage. However the effect on the city climate and indoor temperature is the same.

Communities involvement

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Figure 5-f Public tree nursery

The city government has a very efficient and well-organized informing procedure for local communities and the number of volunteers for helping cool the city is increasing. Also Central Park in Manhattan area, during summer is considered the heart of cool and shade and people realized how much power vegetation can have on the city climate. Therefore one of the most important practices that communities are doing is helping the government create spaces or use the existing parks for public tree nurseries. When trees reach the necessary size, volunteers help the government plant them on streets or in areas where shade is needed.⁷³ As a result, New York City is becoming a greener city. Moreover, through the program NYC ° Cool Roofs and White Roof Project, people volunteer to paint their own roofs white.

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Figure 5-g Volunteers of NYC °CoolRoofs

Chapter 6 New York City vs. Copenhagen

Why New York City and Copenhagen?

In order to illustrate the urban heat island extent in Copenhagen, I decided to make a study case on another city that has a greater potential for creating this phenomenon. The comparison city had to have some common parts with Copenhagen but in the same time be different. I have chosen New York City as study case comparison to Copenhagen because it is one of the most affected city in the world by urban heat island. Both cities are located somehow on a coastal region and the urban climate is strongly influenced by it. Moreover, both cities belong to two different climate zones and have completely different city morphology types. In this way, I could illustrate two different ways of manifestation of urban heat island.

Vegetation

Even though Copenhagen is already a green city, there is a tremendous need for more green areas due to several problems that the city is dealing with. In the same time, New York City is definitely not one of the greenest cities yet, but the issues that the lack of vegetation is creating, made people’s mind to wish to turn it into one.

Programs

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Table 6-a Competitions that both cities won

Both cities have a multitude of ongoing or under development programs, but in Copenhagen the focus is more on storm water management. However the solutions implemented are benefic also to fighting the heat. For heat mitigation New York City has the NYC ° Cool Roofs and White Roof Project and even though white roofs are less efficient than green roofs in heat and storm water matter, they are very cheap and people choose them over green roofs. In Copenhagen this solution cannot be implemented because of the cold climate. They reflect most of the light and during winter they might cool down the indoor temperature.

Major urban changes

Both cities have the will to make major changes to fight the heat. However New York City already made one decision through the program Green light for Midtown when they turned a high traffic area intro an only pedestrian one. Copenhagen has a proposal plan for Åboulevarden to recreate the stream that once was there. Even though the main idea for it is to avoid flooding in that zone, this stream and the vegetation around it will be extended on a large distance and it will definitely prevent any overheating in that area during summer heatwaves.

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Table 6-b Two major projects in the two cities

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Table 6-c Table with green roof projects in Copenhagen

Frederiksberg in Copenhagen is considered as a green island in a red island. Frederiksberg Kommune vision is to be an even greener neighborhood and thus become more attractive and climate proof. Frederiksberg Kommune target is to have a green space not further than 500m from any building⁷⁵.Moreover in Frederiksberg was built the first permeable street, Helenevej.

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Figure 6-g First permeable street in Frederiksberg

Other projects - New York City

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Table 6-d Table with green roofs in New York City

Ideal Copenhagen and New York City

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Figure 6-n Ideal Nordhavn street in Copenhagen Figure 6-0 Ideal boulevard in New York City

Chapter 7 Concluding remarks

Green infrastructure plays an important role in mitigating urban heat island phenomenon. However, creating more greenery inside cities is most of the times a challenge. Cities have been developed during a long period in history and most of the times the historic city center represents the core of the current city. When settlements have started to be modernized, the city core had to fulfill people need for accommodation and services. This lead to an agglomeration of buildings and pavements on a small area and even construction of skyscrapers, while the green spaces and urban climate were forgotten. The result today is a massive amount of materials that absorb and release heat and create urban heat islands.

The urban heat island phenomenon has been studied long before it became a concerning issue for society and when it did, it was almost too late. Currently, the cities cores most of the times are the ones that cause the heat bubbles. However, since people first expressed their concern for environment in 1970, little has been done in greenery and urban climate matter until 2000’s.

With the reducing amount of fossil fuels and raw materials and increasing urban population, society must realize that every destroying action on the land has or will have in the near future a destroying reaction on the urban climate and lifestyle. Therefore preserving and, where already it is lacking, creating new vegetation areas is the best practice to create a climate proof city. Green infrastructure should be seen as a practice of meeting the urban needs today while protecting the ability of future urban development. If sustainable urban planning is defined like this, then every city should aspire to it.

Questionnaires among architects in Copenhagen revealed that they are aware of small temperature differences between city and suburban areas, however they do not consider it a problem. Even though urban heat island is not yet a problem, this report proves that Copenhagen has a potential to develop problematic heat bubbles. This fact is stated in the Copenhagen climate adaption plan with the purpose of avoiding this phenomenon, however architects still do not take it into consideration in planning because it is not currently a problem. On the other hand, a bigger concern in Copenhagen is storm water management and the green infrastructure plan for it will also help preventing urban heat island.

Compared to Copenhagen, New York City has big issues in vegetation and urban climate matter. The urban heat island phenomenon is a very well-known fact among people but the urban core morphology makes it hard for urban planners to fight it. However, the city is opened to any change in order to fight the heat bubbles.

Architects and urban planners shape the world we live in, therefore my conclusion is that if they understand the precise role and effect of each material that they use in the city development, their concepts could make a positive impact on the urban climate. If sustainable urban planning means more green infrastructure and if people in construction industry begin a project with this in mind and understand that not everything that looks good, e.g. skyscrapers, is necessarily good for the urban climate, they could truly deliver greener and cleaner buildings for the environment. Construction industry conception could change only if most of the climatology work would have as objective that the results could be used as guideline in urban planning.

As a conclusion the new kind of architecture together with green infrastructure development, should be seen as “ taking less from the earth and give more to people ” ⁷⁶ . The new modernizing and developing cities will have to be designed as climate proof, because if one thing is unpredictable that is definitely weather.

Abbildung in dieser Leseprobe nicht enthalten

Figure 7-a Let the greenery begin!

Figures table

FIGURE 2-A PICTURE ILLUSTRATES THE DIFFERENCE BETWEEN URBAN BOUNDARY LAYER AND URBAN CANOPY LAYER

TABLE 2-A DIFFERENCE BETWEEN SURFACE AND ATMOSPHERIC TEMPERATURES

FIGURE 2-B PICTURE ILLUSTRATES THE CITY HEAT BUBBLE

FIGURE 2-C PICTURE ILLUSTRATES THE TEMPERATURE DIFFERENCE BETWEEN THE URBAN AND SUBURBAN AREAS

TABLE 2-B ENERGY LOSSES AND ENERGY GAINS

FIGURE 2-D PICTURE ILLUSTRATES HOW RADIATIVE COOLING WORKS ON CLOUDY AND CLOUDLESS NIGHTS

TABLE 2-C TEMPERATURE EQUALIZATION PROCESS

TABLE 2-D URBAN FEATURES' EFFECTS

FIGURE 2-E ALBEDO ILLUSTRATIONS

TABLE 2-E TALL URBAN CANYONS

TABLE 2-F LOW URBAN CANYONS

FIGURE 2-F UPSTREAM URBANIZATION

FIGURE 2-G SHADOW EFFECT IN HIGH URBAN CANYONS

FIGURE 2-H WHEN THE WIND HITS A HIGH BUILDING, THE CURRENT DIVIDES. A PART OF IT GOES UP, ON TOP OF THE BUILDING AND THE REST GOES AROUND IT. THE PICTURE SHOWS THAT ONLY THE UPPER PART OF THE URBAN CANOPY LAYER GETS VENTILATED.

FIGURE 2-I SHADE EFFECT IN LOW URBAN CANYONS

FIGURE 2-J LACK OF VEGETATION WITHIN A CITY

FIGURE 2-K HEAT BUBBLE EFFECT ON CLOUDS

FIGURE 3-A PAINTING THE ROOF WHITE

FIGURE 3-B PERVIOUS CONCRETE

FIGURE 3-C POROUS ASPHALT VS. CONVENTIONAL ASPHALT PERFORMANCE

FIGURE 3-D POROUS ASPHALT VS. CONVENTIONAL ASPHALT TEXTURE

FIGURE 3-E RESIN BOUND PERMEABLE PAVEMENT

FIGURE 3-F CUBIC STONE PAVEMENT

FIGURE 3-G PERMEABLE INTERLOCKING CONCRETE PAVEMENT

FIGURE 3-H PERMEABLE INTERLOCKING CLAY BRICK TILES PAVEMENT

FIGURE 3-I RECYCLED GLASS POROUS PAVEMENT

FIGURE 3-J PERMEABLE GRASS PAVEMENT

FIGURE 3-K PERMEABLE TURF PAVEMENT

FIGURE 3-L GREEN INFRASTRUCTURE ILLUSTRATION

FIGURE 3-M GREEN ROOF STRUCTURE

TABLE 3-A TABLE CONTAINS A CROSS-SECTION FROM EACH TYPE OF GREEN ROOF

FIGURE 3-N MODULAR GREEN ROOF APPEARANCE

FIGURE 3-O GREEN WALL

FIGURE 3-P GREEN FAÇADE EXAMPLE

FIGURE 3-Q LIVING WALL EXAMPLE

FIGURE 3-R TREE SHADE

FIGURE 3-S TREE SPACING

FIGURE 3-T GREEN ROOFS AND GREEN WALLS ILLUSTRATION

FIGURE 3-U LIVING WALLS AND GREEN FAÇADE COMPARISON

TABLE 3-B COMPARISON BETWEEN LIVING WALLS, GREEN FAÇADES AND GREEN ROOFS

FIGURE 3-V COMPARISON BETWEEN A NORMAL BUILDING AND A BUILDING COVERED WITH GREEN ROOF AND LIVING WALL

FIGURE 3-W COMPARISON BETWEEN LIVING WALL AND GREEN FAÇADE ON IMPACT ON INDOOR TEMPERATURE

TABLE 3-C COMPARISON BETWEEN LIVING WALLS, GREEN FAÇADES AND GREEN ROOFS

FIGURE 3-X GREEN ROOF GARDEN

FIGURE 3-Y HIGH URBAN CANYON SPACE BETWEEN BUILDINGS

FIGURE 3-Z HIGH URBAN CANYON GREEN ROOFS AND LIVING WALLS

FIGURE 3-AA LOW URBAN CANYON AIR CIRCULATION BETWEEN GREEN ROOFS AND LIVING WALLS

FIGURE 3-BB GROUND TO ROOF CONNECTION METHOD

TABLE 4-A THESE TABLES ILLUSTRATE THE CLIMATE WITHIN THE LAST TEN YEARS IN COPENHAGEN

FIGURE 4-A COPENHAGEN MEAN OF TRANSPORATION

FIGURE 4-B THE MAPS SHOW THE MAXIMUM SURFACE TEMPERATURES ON THE 2ND OF JUNE 2006, 18TH OF JUNE 2006, 20TH OF JULY 2006, 22ND OF SEPTEMBER 2006

TABLE 4-B THIS CHART SHOWS THE AVERAGE SURFACE TEMPERATURE DIFFERENCES BETWEEN FIVE DIFFERENT URBANIZED ZONES IN COPENHAGEN AREA IN THE FOUR CHOSEN DAYS

TABLE 4-C IN ORDER TO HAVE A BETTER UNDERSTANDING OF THE DATA IN THE MAPS, THIS TABLE SHOWS A BETWEEN THE AIR TEMPERATURE AND SURFACE TEMPERATURES DURING DAYTIME IN THE SPECIFIC FOUR DAYS

TABLE 4-D THIS CHART SHOWS THE TEMPERATURE DIFFERENCE BETWEEN DAY AND NIGHT IN THE SPECIFIC FOUR CHOSEN DAYS.

TABLE 4-E THESE TWO CHARTS CONTAIN INFORMATION ABOUT THE WIND SPEED AND HUMIDITY IN THESE 4 DAYS.

FIGURE 4-C COPENHAGEN SATELLITE VIEW

FIGURE 4-D THIS MAP SHOWS THE LOCATION OF POCKET PARKS

FIGURE 4-E THIS MAP DEMONSTRATES THAT THERE IS A SIGNIFICANT NUMBER OF PARKS AND VEGETATED AREAS WITHIN THE CITY AND THAT THE GOAL OF A SHORT WALKING DISTANCE TO ANY OF THEM IS VERY EASY TO

ACHIEVE.

TABLE 4-F THIS STATISTIC PROVES THAT THE TARGET HAS BEEN ACHIEVED THIS YEAR AND IS EXPECTED TO INCREASE

IN THE NEXT YEARS.

FIGURE 4-F THIS MAP SHOWS THE FLOOD RISK IN COPENHAGEN AND THEREFORE IS REPRESENTATIVE FOR THE IMPERMEABLE MATERIALS THAT COVER THE CITY

FIGURE 4-G INDOOR TEMPERATURE

FIGURE 4-H COPENHAGEN SUMMER

TABLE 4-G COPENHAGEN CLIMATE ADAPTION PLAN PLANNING

TABLE 5-A THESE TABLES ILLUSTRATE THE CLIMATE WITHIN THE LAST TEN YEARS IN NEW YORK CITY

FIGURE 5-A MANHATTAN MAP

FIGURE 5-B THIS TABLE SHOWS THE PERCENTAGES OF VEGETATION AND IMPERVIOUS SURFACES IN SOME OF THE NEW YORK CITY NEIGHBORHOODS. THE PERCENTAGES ARE COMPARATIVE TO THE SPECIFIC ZONE.

FIGURE 5-C MAP OF NEW YORK CITY WITH WHITE ROOFS AT THE END OF 2012

FIGURE 5-D WHITE ROOF PROJECT RESEARCH

FIGURE 5-E THE TRUMP TOWER IN NEW YORK CITY - TREES ARE PLANTED ON BUILDINGS TERRACES AT DIFFERENT LEVELS

FIGURE 5-F PUBLIC TREE NURSERY

FIGURE 5-G VOLUNTEERS OF NYC °COOLROOFS

TABLE 6-A COMPETITIONS THAT BOTH CITIES WON

TABLE 6-B TWO MAJOR PROJECTS IN THE TWO CITIES

FIGURE 6-A 8TALLET - 1700M2 OF GREEN ROOF

FIGURE 6-B VM MOUNTAIN

FIGURE 6-C THE NATIONAL ARCHIVES - 7200M2 GREEN ROOF GARDEN WITH INTEGRATED CYCLE TRACK

FIGURE 6-E GREEN FAÇADE ON DET KONGELIGE BIBLIOTEKS GAMLE HOVEDBYGNING

FIGURE 6-F GREEN FAÇADE AT VESTERPORT STATION

TABLE 6-C TABLE WITH GREEN ROOF PROJECTS IN COPENHAGEN

FIGURE 6-G FIRST PERMEABLE STREET IN FREDERIKSBERG

FIGURE 6-H NEW YORK CITY COUNTY COURTHOUSE - 929M2 OF SEMI-INTENSIVE GREEN ROOF

FIGURE 6-I MANHATTAN UNION SQUARE CONDOMINIUM - 1765M2 OF SEMI-INTENSIVE GREEN ROOF

FIGURE 6-J MANHATTAN JAVITS CONVENTION CENTER - 27300M2 OF EXTENSIVE GREEN ROOF

FIGURE 6-K MANHATTAN MIDTTOWN HIGH RISE - 650M2 OF INTENSIVE GREEN ROOF

FIGURE 6-L LIVING WALL ON 37 WARREN STREET, NEW YORK CITY

FIGURE 6-M LIVING WALL IN LA GUARDIA NEW YORK CITY AIRPORT

TABLE 6-D TABLE WITH GREEN ROOFS IN NEW YORK CITY

FIGURE 6-N IDEAL NORDHAVN STREET IN COPENHAGEN

FIGURE 6-O IDEAL BOULEVARD IN NEW YORK CITY

FIGURE 7-A LET THE GREENERY BEGIN!

Figures sources

Abbildung in dieser Leseprobe nicht enthalten

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[...]

---

¹ Paragraph information from - Day, G., Gould, E., & Organ, M., 1998. History of sustainability. [online]

² Quote from - Elliot, M. (Director), 2013. The urban heat island explained on The Weather Channel

³ Howard, L., 1818-20. The climate of London: deduced from Meteorological Observations, made at different places in the neighborhood of the metropolis (1st ed., Vol. I). London

⁴ Mills, G., 2004. IAUC Teaching Resources The Urban Canopy Layer Heat Island

⁵ Information from - Wikipedia, 2001. Urban heat island. [online]

⁶ Quote from - Voogt, J. A., 2004. Urban Heat Islands: Hotter Cities. [Online]

⁷ Quote from - Voogt, J. A., 2004. Urban Heat Islands: Hotter Cities. [Online]

⁸ Quote from - Wikipedia, 2003. Radiative cooling. [online]

⁹ Both ratios are a relative measurement.

¹⁰ Quote from - Upton, J., 2014. To cool cities, build them tall and shiny. [online]

¹¹ Paragraph information from - Kusaka, H., Kimura, F., 2004. Thermal Effects of Urban Canyon Structure on the Nocturnal Heat Island: Numerical Experiment Using a Mesoscale Model Coupled with an Urban Canopy Model. American Meteorological Society.

¹² Quote from - Elliot, M. (Director). (2013). The urban heat island explained on The Weather Channel

¹³ Also known as tar

¹⁴ Quote from - Sika. Green roof. [online]

¹⁵ Usually plywood

¹⁶ Quote from - Gaffin, S. (Producer), 2009. Hot cities: The urban heat island effect

¹⁷ Paragraph information form - Zhao, L., Lee, X., Smith, R. B., Oleson, K., 2014, July 10. Strong contributions of local background climate tourban heat islands. Nature, 511

¹⁸ Paragraph information from - Doick, K., & Hutchings, T., 2013, February. Air temperature regulation by urban trees and green infrastructure.

¹⁹ Paragraph information from - Ca, V. T., Asaeda, T., Abu, E. M., 1996. Reductions in air conditioning energy caused by a nearby park. Saitama University

²⁰ Akbarit, H., Pomerantz, M., & Taza, H., 2001. Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas

²¹ Information from - Use vegetation to increase energy efficiency. [online]

²² Information from - American Society of Landscape Architects, 2012. Urban forests=Cleaner, cooler air

²³ Natural England, 2010. Nature nearby' Accessible natural greenspace guidance. Natural England.

²⁴ Quote from - Moisse, K., 2010, February 2. Over the Top: Data Show "Green" Roofs Could Cool Urban Heat Islands and Boost Water Conservation. [online]

²⁵ Doick, K., & Hutchings, T., 2013, February. Air temperature regulation by urban trees and green infrastructure.

²⁶ Information from - Gaffin, S. (Producer), 2009. Hot cities: The urban heat island effect

²⁷ LEED® stands for Leadership in Energy and Environmental Design and is a program developed by the U.S. Green Building Council. It is an internationally green building certification system that gives credits (LEED® credits) for different categories: sustainability, energy savings, indoor air quality, health & wellness and acoustics.

²⁸ Temperatures from - Tilley, D., Price, J., Matt, S., & Marrow, B., 2012. Vegetated Walls: Thermal and Growth Properties of Structured Green Fa ç ades

²⁹ Paragraph information from - Garrison, N., Horowitz, C., & Lunghino, C. A., 2012. Looking Up: How Green Roofs and Cool Roofs Can Reduce Energy Use, Address Climate Change, and Protect Water Resources in Southern California.

³⁰ Ottelé, M., 2011. The green building envelope Vertical greening

³¹ Information from - Michigan State University, Department of Horticulture., 2006. The Role of Extensive Green Roofs in Sustainable Development

³² Tanner, S., & Scholz-Barth, K., 2004. Federal energy management program - Green roofs. U.S. Department of Energy

³³ Temperature for living wall placed indoor - Green over gray, 2009. LEED ® Credits. [online]

³⁴ Temperature from - Tilley, D., Price, J., Matt, S., & Marrow, B., 2012. Vegetated Walls: Thermal and Growth Properties of Structured Green Fa ç ades

³⁵ Djedjig, R., Bozonnet, E., & Belarbi, R., 2013. Experimental study of the urban microclimate mitigation potential of green roofs and green walls in street canyons

³⁶ Paragraph information from - Hopkins, G., & Goodwin, C., 2011. Living Architecture: Green Roofs and Walls

³⁷ World weather and climate., 2013. Average weather and climate in Denmark. [online]

³⁸ Københavns Kommune, Miljø Metropolen., 2011. Copenhagen climate adaption plan.

³⁹ The process of creating new land from ocean, riverbeds, or lakes

⁴⁰ Weather online. Climate robot. [online]

⁴¹ Københavns Kommune, Miljø Metropolen., 2011. Copenhagen climate adaption plan.

⁴² Københavns Kommune., 2013, June 13. Bicycle statistics. [online]

⁴³ It should be emphasized that this study is made on the basis of measurements in only four days in one single year, therefore it should not be considered as a general rule.

⁴⁴ Paragraph information from - Esbirk, D. I., & Junker, B., 2010. Klimatilpasning - Byforgr ø nnelse som middel til bym æ ssig b æ redygtighed.

⁴⁵ Københavns Kommune, Miljø Metropolen., 2011. Copenhagen climate adaption plan.

⁴⁶ See Table 4-g

⁴⁷ Pocket parks are small parks with an area less than 5000m 2. They are called pocket parks because they are usually made around a monument or to fill in a gap in the city.

⁴⁸ DAC., 2014, January 21. K Ø BENHAVN: LOMMEPARKER - GR Ø NNE Å NDEHULLER I BYEN.

⁴⁹ Rømø, D., 2011. Green roofs in Copenhagen. [online]

⁵⁰ Paragraph information from - Hvass, J., 2005. GR Ø NNE LUNGER

⁵¹ Københavns Kommune, Miljø Metropolen., 2011. Copenhagen climate adaption plan.

⁵² European Environment Agency. (2013). Climate change and flood risk in European cities. [online]

⁵³ Rosenbak, M., & Carstensen, T. A, 2009. Den klimavenlige by - ø kologiske potentialer.

⁵⁴ The Danish Ministry of Economic and Business Affairs; Danish Enterprise and Construction Authority. (2010). Building Regulations 2010

⁵⁵ Calculations are made specifically for every project

⁵⁶ Paragraph information from - Københavns Kommune, 2014. K ø benhavns Klimakarr é

⁵⁷ See Appendix 3

⁵⁸ Københavns Kommune, Miljø Metropolen., 2011. Copenhagen climate adaption plan.

⁵⁹ Weather online. Climate robot. [online]

⁶⁰ Slosberg, R. B., Rosenzweig, C., & Solecki, W. D., 2007. New York City Regional Heat Island Initiative: Mitigating New York City ’ s Heat Island with Urban Forestry, Living Roofs, and Light Surfaces

⁶¹ Gaffin, et al., 2007. Variations in New York city ’ s urban heat island strength over time and space

⁶² NYC Parks. Green Infrastructure. [online]

⁶³ Myor's Office of Long-Term Planning and Sustainability, 2014. PLANYC Progress report 2014

⁶⁴ NASA. The Making (and Breaking) of an Urban Heat Island. [online]

⁶⁵ New York City Department of Transportation, 2010. Green Light for Midtown Evaluation Report

⁶⁶ New York City Depertment of Transportation. Pedestrians - Broadway. [online]

⁶⁷ NYC °Cool Roofs, 2012. NYC ° Cool Roofs Annual review 2012.

⁶⁸ White roof project is a continuity project of NYC °Cool Roofs White Roof Project, 2010. White Roof Project. [online]

⁶⁹ A Local Law to amend the administrative code of the city of New York and the New York city building code, in relation to roof coating standards, 347-A (January 1, 2012)

⁷⁰ See Figure 5-d

⁷¹ NYC °Cool Roofs, 2014. NYC ° Cool Roofs. [online]

⁷² Rosenzweig, C., Solecki, W. D., Parshall, L., Lynn, B., Cox, J., Goldberg, R., . . . Watson, M., 2009. MITIGATING NEW YORK CITY ’ S HEAT ISLAND Integrating Stakeholder Perspectives and Scientific Evaluation.

⁷³ American Society of Landscape Architects (Producer), 2012. Urban forests=Cleaner, cooler air

⁷⁴ København Kommune, 2014. Å ben Å en. [online]

⁷⁵ Frederiksberg Kommune, 2012. Sektorplan 2012 Byrum og Gr ø nne Omr å der.

⁷⁶ Barnett, D. L., & Browning, W. D., 2007. A PRIMER ON SUSTAINABLE BUILDING