The Urban Heat Island Phenomenon in Malaysia.doc New

 THE URBAN HEAT ISLAND PHENOMENON IN MALAYSIA Ramu velusamy Politeknik Ungku Omar Perak Abstract

Urban heat island (UHI) is not a new phenomena for many of the mega cities in the world today. It also experienced by most of of the big cities in Malaysia since since the last few decades. Since most of  the build environment environment in Malaysia are concrete jungle in stand of mixture of concrete structures structures and green vegetations or some other building materials which has low heat carrying capacity, the temperature temperature increases increases event event at night or comparing comparing with with the surroundi surrounding ng areas(rural areas(rural)) . Urban Heat Island (UHI) refers to the tendency for a city to remain warmer than its surroundings. This effects is caused mostly by the lack of vegetation and soil moisture, which would normally use much much of the absorbed absorbed sunligh sunlightt to evapo evaporat ratee water water as part part of the photosyn photosynthe thesi siss ( a proces processs called called evapotrans evapotranspirat piration). ion). Instead Instead , the sunlight sunlight is absorbed absorbed by manmade manmade structures structures : roads, roads,  parking lots, and buildings. With little or no water to evaporate, the sunlight’s energy goes into raising the temperature of those surface. After the sun sets, the city is so warm that it never cools down as much as the country side around it, and so retain the heat island effects all night long. Most researches of UHI discuss the environment issues of urban heat island in relation to rapid urban development development and industria industriall factors factors which tend to alter alter natural natural patterns patterns and trends trends of  temperatures within the urban urban environment. The selection selection of building materials is significant significant for  the therm thermal al perfor performan mance ce of build building ing facade facadess and the the urban urban therma thermall enviro environme nment nt . A Vital Vital mitigation process has has to be implemented to reduce the urban surface temperature temperature and create a livable city Key word : urban heat island, thermal comfort, livable city, surface temperature, evaporation, evapotranspiration

An urban heat island (UHI) is a metropolitan area which is significantly warmer than its surrounding rural areas. The phenomenon was first investigated and described by Luke Howard in the 1810s, although he was not the one to name the phenomenon. ( en.wikip en.wikipedia.or edia.org/wiki/ g/wiki/ Heat_isla Heat_island nd ). The term "heat island" refers to urban air and surface temperatures that are higher than nearby rural areas. Many cities and suburbs have air temperatures that are 2 to 10°F (1 to 6°C) warmer than the surrounding natural land cover .. It demonstrates how urban temperatures are typically lower at the urban-rural border than in dense downtown areas. (The Encyclopedia of earth , june 29.2 .20 010 by Cutter Cleveland , (http://www.eoearth.org/article/Heat_island ) Urban and suburban areas have long been observed to have heat island, a ‘ reverse oasis’ where air and surface temperatures are hotter than their rural surroundings. The heat island phenomenon has been found in cities cities throu throughgh-out out the world. world. The first docum document entati ation on of urban urban heat heat occurs occurs in 1818 1818 when when Luke Luke Howard’s ground- breaking study of London’s climate found an artificial excess of heat in the city compared with the country ( Howard, 1833). Emilien Renou made similar discoveries about Paris during the second half of the 19 th century and Wilhelm Schmidt found these condition in Vienna early in the 20 th century (Schmidt, 1917,1929). Study of heat island in the US began in the first of the 20 th century ( Mitchell, 1953, 1961). In Malaysia UKM are doing research on this heat island. Green roof is one of the solution for it. ( Shaharudin Ahmad, Noorazuan Md Hashim, Yaakob Mohd Jani 2007) Heat islands form in urban and suburban areas because many common construction materials absorb and retain more of the sun’s heat than natural materials in less-developed rural areas. Concrete is the main  building materials used in most housing scheme in Malaysia. Surface temperature for concrete is higher  than wood during the day time. time. Concrete having heat caring capacity greater greater compare to timber. There are two main main reason reasonss for this this heatin heating. g. First, First, most most urban urban buildi building ng materi materials als are imperm impermeab eable le and watertight, so moisture is not readily available to dissipate the sun’s heat. Second, dark materials such as  premix and pavement collect and trap more of the sun’s energy. Temperatures of dark, dry surface in direct sun can reach up to 50 oc during the day, while vegetated surface with moist soil under the

same conditions might reach only 25oc. Anthropogeni Anthropogenicc heat, or human-produced human-produced heat, heat, slower  wind speeds and air pollution in urban areas also contribute to heat island formation. Is our  housing scheme is a livable for all?

Heat island exhibit five common characteristic. •

When compared to undeveloped, rural areas, a heat island is warmer in general, with distinct daily patterns of behavior, behavior, Heat island are often warmest, warmest, relative to rural surroundings, surroundings, after the sun goes down, and coolest after the sun rises. Urban air in the ‘ canopy layer, below the tops

of trees and building, can be as much as 6o c warmer than the air in rural areas. •

Air temperature are driven by the heating of urban surface, since many man-made surface absorb more of the sun’s heat than natural vegetation does.

•

These differences in air and surface temperatures are enhanced when the weather is calm and clear.

•

Areas with the least vegetation and greatest development tend to be hottest and heats island tend to become more intense as cities grow larger.

There are several other reasons for the heat island phenomenon. Urban heat generation form heating, cooling, transportation and industrial processes. But what causes these phenomena? As explained above, there is no single cause of the heat island. Instead, many factors combine to warm cities and suburbs. The leading urban characteristics contributing to heat island formation. These characteristics can be stored into the five main cause of heat island formation: •

Reduced evaporation

•

Increased heat storage

•

Increased net radiation

•

Reduced convection

•

Increased anthropogenic heat

Urban and suburban characteristic important to heat island formation and their on the energy balance of  the earth’s surface.

Characteristic contributing to heat island formation Lack of Vegetation

Effect on the energy balance Reduces evaporation

Widespread use of impermeable surfaces Reduces evaporation Increased thermal diffusivity of urban materials Increase heat storage Low solar reflectance of urban materials Increases net radian Urban geometries that trap heat Increases net radian Urban geometries that slow wind speeds Reduces convection Increased energy use Increases anthropogenic heat. An equation called the ‘ energy balance’  explains how energy is transferred to and from the Earth’s surface. The energy balance is based on the first law of thermodynamics, which states that energy is never  lost. For a surface on the Earth, this means that all energy absorbed by the the surface through radiation or  from anthropogenic heat goes somewhere. Either it warms the air above the surface, is evaporated away with moisture or is stored stored in the material as heat. The energy balance equation is: is: CONVECTION + EVAPORATION + HEAT STORAGE = ANTHROPOGENIC HEAT + NET RADIATIO

Convection is energy that is transferred from a solid surface to a fluid ( i.e. a liquid or gas), in this case from the Earth’s surface to air above it. Convection increases when wind speeds are higher, when air   become more turbulent differences between the surface and the air are bigger. Evaporation is energy transmitted away from the Earth’s surface by water vapor. Water from moist soil, vegetation or wet surface to vapor when heated by the sun other source. Water vapors then rises into the atmosphere, taking the sun’s energy with it. The evaporation tern also includes evapotranspirataion, a more complicated process plants use to keep cool. During evapotranspiration, water is drawn from the soil by the roots of the plant and is evaporated through stomata on the plants leaves. Both evaporation and evapotranspiration increase when there is more moisture available, when wind speeds are grater and when the air is drier and warmer.

Heat storage depends on two properties of materials: their thermal conductivity and heat capacity. Materials with high thermal conductivity are more able to direct heat into their depth. Materials with high capacity can store more heat in their bulk. As more heat is stored, the temperature of the material rises. Anthropogenic heat represents ‘ man-made’ heat generated by building, machinery or people. In many areas, especially rural and suburban areas, the amount of anthropogenic energy is small compared to the other terms in the balance equation. In dense urban areas, the anthropogenic term is larger and can be a significant influence on heat island formation.  Net radiation encompasses four separate radiation processes taking place at the Earth’s surface.   NET RADIATION = INCOMING SOLAR-RECFLECTED SOLAR+ ATMOSPHERIC RADIATIONSURFACE RADIATION INCOMING SOLAR  represents the amount of energy radiating from the sun. This obviously varies  based on the season, the time of day ( zero at night), the amount of cloud cover and the atmospheric  pollution levels. REFLECTED SOLAR  radiation is the amount of solar energy that bounce off a surface, based on the solar reflectance of the materials. Surface with high solar reflectance, such as bright white roofing materials, reflect most of the solar radiation that falls on them, whereas dark surface such as asphalt  pavement absorb most of the solar radiation. ATMOSPHERIC RADIATION is heat emitted by particles in the atmosphere, such as water vapors droplets, clouds, pollution and dust. The warmer the atmosphere and the more particles it contains, the more energy it emits.

radiated from a surface surface itself. This term is highly dependent dependent on the SURFACE RADIATIONS is heat radiated temperatures of the surface and its surroundings. A relatively warmer surface radiates more energy to its surroundings.

RESEARCH CARRIED OUT ON HOW SURFACE TEMPERATURE CONTRIBUTED CONTRIBUTED TO URBAN HEAT ISLAND (UHT) PROBLEM PROBLEM IN UNGU OMAR POLYTECHNIC

As we know most of the building materials can absorbed more heat during day time. Each and every  building materials has its on heat carrying capacity. Through this research I would like to prove that,  building  building materials materials are one of the main factors in contributin contributing g to Urban Heat Island. Island. Due to this, two materials are tested. Brick walls and and premix are taken. The materials are tested tested in two condition condition , shaded with vegetation and exposed to direct sunlight.

Below are the data’s collected in Ungku Omar Omar Polytechnic on concrete and premix surface with shaded and not shaded with vegetations vegetations . Data are collected for for five days. Infrared thermometer is used :

Concrete surface C o 8am concrete surface ( unshaded) concrete surface (shaded)

10am

12am

3pm

5pm

7pm

25.5

Co

32.7

Co

33

Co

33.9

Co

32.8

Co

31.1

Co

25.7

Co

27

Co

28.1

Co

28.9

Co

29.9

Co

29.4

Co

Concrete surface which unshaded get heated faster than shaded concrete surface. Even at 7pm, the temperatur temperaturee shows shows 31.1C0 compar compared ed to shaded shaded just just 29.4C 29.4C0. To reduce Urban Urban Heat Heat island island , more more vegetation have to be planted around buildings. buildings.

Premix surface Co

8am premix surface ( unshaded) c

28.2

Co

10am 30.6

Co

12am 52

Co

3pm 44

Co

5pm 37.1

Co

7pm 33.7

Co

premix surface (shaded) c

25.8

Co

27.4

Co

30

Co

37

Co

32

Co

28.7

Co

Premix surface which unshaded get heat faster than shaded premix surface. Even at 7pm, the temperature shows 33.7 C 0 compared to shaded just 28.7C 0. To reduce Urban Heat island , most of the car park park area has to be located under a big trees or coved .

REDUCING REDUCING HEATS HEATS ISLAND ISLANDS S PROBLE PROBLEM M IN MALAYSIA MALAYSIA BY USING USING TREES AND VEGETATION : COMPENDIUM COMPENDIUM OF STRATEGIES

Shade trees and smaller plants such as shrubs, vines, grasses, and ground cover, help cool the URBAN environment. Yet, many Malaysian communities have lost trees and green space as they have grown. This change is not inevitable. Many communities can take advantage of existing space, such as grassy or   barren areas, to increase their vegetative cover and reap multiple benefits.

Trees and vegetation help cool housing urban climates through shading and evapotranspiration. Shading. Leaves and branches reduce the amount of solar radiation that reaches the area below the canopy of a tree or plant. The amount of sunlight transmitted through the canopy varies based on plant species. Generally 10 to 30% of sun’s energy reaches the area below a tree, with the remainder being absorbed by leaves and used for photosynthesis, and some being reflected back into the atmosphere. (Huang, J., H. Akbari, and H. Taha.) Shading reduces surface temperatures below the tree canopy. These cooler surfaces, in turn, reduce the heat transmitted into buildings and the atmosphere. For example, a multi-month study measured maximum surface temperature reductions ranging from 20 to 45ºF (11-25ºC) for walls and roofs at two buildings (Akbari, H., D. Kurn, S. Bretz, and J. Hanford) . Another study examined the effects of vines on wall temperatures and found reductions of up to 36ºF (20ºC). (Sandifer, S. and B. Givoni) A third study found that tree shading reduces the temperatures inside parked cars by about 45ºF (25ºC). (Scott, K., J.R. Simpson, and E.G. McPherson) Evapotranspiration. Trees and vegetation absorb water through their roots and emit it through their  leaves—this movement of water is called “transpiration.” A large oak tree, for example, can transpire 40,000 gallons of water per year; an acre of corn can transpire 3,000 to 4,000 gallons a day. (U.S. Geological Survey.) Evaporation, the conversion of water from a liquid to a gas, also occurs from the soil around vegetation and from trees and vegetation as they intercept rainfall on leaves and other surfaces. Together, these processes are referred to as evapotranspiration. Evapotranspiration cools the air by using heat from the air to evaporate water. Trees and other large vegetation can also serve as windbreaks or  wind shields to reduce the wind speed in the vicinity of buildings buildings and the impacts can be positive and negative.

Plants take water from the ground through their roots and emit it through their leaves, a process known as transpiration. Water can also evaporate from tree surface, such the stalk, or surrounding soil. Trees and vegetation are most useful as a mitigation strategy when planted in strategic locations around  buildings. Researchers have found that planning deciduous species to the west is typically most effective for cooling a building, especially if these trees shade windows and part of the building’s roof. Shading the east side of a structure also reduces air conditioning demand. (Simpson, J.R., and E.G. McPherson) Planting trees to the south generally lowers energy demand, but must be done carefully. Depending on the trees, trees, the buildi building ng’s ’s height height,, and the dista distance nce betwe between en the trees trees and a buildi building, ng, trees trees may be detrimental to an energy efficiency strategy if they block useful solar energy. Shading pavement in  parking lots and on streets can be an effective way to help cool a community. Trees can be planted around  perimeters and in medians inside parking lots or long the length of streets. Strategically placed shade trees also can benefit playground, schoolyards ,ball fields and similar open spaces.

Blocked sunlight by evergreen trees

PICKING THE RIGHT TREES AND PITTING THEM IN THE RIGHT LOCATION WILL MAXIMIZE THEIR ABILITY TO SHADE BUILDING AND BLOCKED SUNLIGHT THROUGHT THE YEAR

Trees are not the only vegetation option. There are many areas where trees either do not fit or grow too slowly to be effective over the short term, in which case vines may work better. Vines need less soil and space and grow very quickly. Vines grown on the west side of a building, for example, will shade the exterior wall and reducing heat gain inside the building. building. The vines will provide some air cooling benefits benefits through evepotranspiration as well. The use of trees and vegetation in the URBAN URBAN area environment brings many benefits, benefits, including lower  energy use, reduced air pollution and greenhouse gas emissions, protection from harmful exposure to ultraviolet (UV) rays, decreased storm water runoff, potential reduced pavement maintenance and other  quality of life benefits . Reduced Energy Use.

Trees and vegetation that provide direct shading reduce energy needed to cool buildings. Benefits vary  based on the orientation and size of the plantings, as well as their distance from a building. Large trees  planted close to the west side of a building will generally provide greater cooling energy savings than other plants.

•

Joint Joint studi studies es by the Lawren Lawrence ce Berkel Berkeley ey Nation National al Labora Laborator tory y (LBNL) (LBNL) and the Sacram Sacrament ento o Municipal Utility District (SMUD) placed varying numbers of trees around houses to shade windows and then measured the buildings’ energy use. 8 The cooling energy savings ranged  between  between 7 and 47 percent percent and were were greatest greatest when when trees were plante planted d to the east and west of   buildings. ( H. Akbari, S. Bretz, J. Hanford, D. Kurn, B. Fishman, H. Taha, and W. Bos )

Reduced Air Pollution and Greenhouse Gas Emissions.

In addition to saving energy, the use of trees and vegetation as a mitigation strategy can provide air  quality and greenhouse gas benefits: •

Leaves remove various pollutants from the air, referred to as “dry deposition”

•

Shade trees reduce evaporative emissions from parked vehicles

•

Trees and vegetation remove and store carbon

•

Trees and vegetation reduce greenhouse gas emissions from power plants by reducing energy demand.

Pollutant Removal through Dry Deposition.

Plants generally take up gaseous pollutants, primarily through leaf stomata, that then react with water  inside the plant to form acids and other chemicals. Plants can also intercept particulate matter as wind currents blow particulates into contact with the plants’ surfaces. Some particulates are absorbed into the  plant while others adhere to the surface, where they can be resuspended into the atmosphere by winds or  washed off by rain to the soil beneath. (Nowak, D.J.) These processes can reduce various pollutants found in the urban environment, including particulate matter (PM), nitrogen oxides (NO X), sulfur dioxide (SO 2), carbon monoxide (CO), and ground-level ozone (O 3). Reduced Evaporative Emissions.

Tree Tree shade shade can keep keep parked parked cars—p cars—part articu icular larly ly their their gas tanks— tanks—coo cooler ler,, which which lowers lowers evapor evaporati ative ve emissions of volatile organic compounds (VOCs), a critical precursor pollutant in the formation of  ground-level ozone. Most large urban areas have a wide range of control programs to reduce these emissions, and tree shading programs can be part of those strategies. For example, one analysis predicted that light-duty vehicle evaporative VOC emission rates throughout Sacramento County could be reduced  by 2 percent per day if the community increased the tree canopy over parking lots from 8 to 50 percent. (Scott, K., J.R. Simpson, and E.G. McPherson) Carbon Storage and Sequestration.

As trees grow, they remove carbon from the atmosphere and store, or sequester, it. As trees die or  deposit litter and debris on the ground, carbon is released to the atmosphere or transferred to the soil. The net effect of this carbon cycle is a substantial level of carbon storage in trees, vegetation, and soils. The net rate of carbon sequestered by urban trees in the continental United States in 2005 is estimated to have  been around 24 million tons per year (88.5 million tons CO 2eq) , while current total carbon storage in urban trees in the continental United States is approximately 700 million tons of carbon. The national average urban forest carbon storage density is just over 25 tons per hectare (100,000 square feet, or 9,300 m2), but varies widely from one community to another and corresponds generally to the percentage of  land with tree cover and to tree tree size and health ( Nowak, D.J. and D.E. Crane.) Reduction in Greenhouse Gas Emissions through Reduced Energy Demand.

As noted above, trees and vegetation can decrease energy demand. To the extent that reduced energy consumption decreases fossil fuel burning in power plants, trees and vegetation also contribute to lower  carbon emissions from those power plants. One modeling study estimated that the direct energy savings from shading alone by trees and vegetation could reduce carbon emissions in various U.S. metropolitan areas by roughly 1.5 to 5 percent (Konopacki, S. and H. Akbari. 2002) . The study assumed that eight shade trees would  be placed strategically around residential and office buildings and four around retail stores. As urban forests also contribute to air temperature reductions, the study found that there would be additional reductions in energy use and carbon emissions from those indirect effects as well. Improved Human Health.

By reducing air pollution, trees and vegetation lower the negative health consequences of poor air  quality. Also, similar to the benefits of cool roofs discussed in the “Cool Roof” chapter, shade trees can reduce heat gain in buildings, which can help lower indoor air temperatures and minimize the health impacts from summertime heat waves. A third health benefit from trees and vegetation involves reducing direct exposure to UV rays. The sun’s UV rays can have adverse health effects on the skin and eyes. High levels of long-term exposure to UV rays are linked to skin cancer. The shade provided by dense tree canopies can help to lower UV exposure, although this should not be considered a primary preventive measure. (Heisler, G.M. and R.H. Grant. 2000 ) Enhanced Storm water Management and Water Quality.

Urban forests, vegetation, and soils can reduce storm water runoff and adverse impacts to water  resources. Trees and vegetation intercept rainfall, and the exposed soils associated with plants absorb water that will be returned to ground water systems or used by plants. Rainfall interception works best during small rain events, which account for m ost precipitation. With large rainfalls that continue beyond a certain threshold, vegetation begins to lose its ability to intercept water. Storm water retention further  varies by the extent and nature of a community’s urban forest ( Xiao, Q., E.G. McPherson, J.R. Simpson, and S.L. Ustin. 1998 ). Reduced Pavement Maintenance Costs.

Tree shade can reduce the deterioration of street pavement. One field study compared pavement condition data based on different amounts of tree shade ( McPherson, E.G. and J. Muchnick. Muchnick. 2005) . The study found that slurry resurfacing costs on a residential street could be reduced by approximately 15 to 60  percent, depending on the type of shade trees used. Although the specific costs and benefits will vary  based on local conditions and paving practices, the study suggests that pavement maintenance benefits are another area to consider in evaluating the potential benefits of a street shade tree program. Enhanced Quality of Life.

Trees and vegetation can provide a range of quality-of life benefits. Adding trees and vegetation to urban parks, streets, parking lots, or roofs can provide a habitat for birds, insects, and other living things. A well-placed row of trees and shrubs can reduce urban noise by 3 to 5 decibels, while wide, dense belts of mature trees can reduce noise by twice that amount, which would be comparable to noise reduction from effective highway barriers ( Nowak, D.J. and J.F. Dwyer. 2007 ). Urban trees and vegetation have been linked to reduced crime (Kuo, Francis E. and W.C. Sullivan. 2001), increased property values ( Laverne, R.J. and K. Winson-Geideman. ) Wolf, 2003 , and other psychological and social benefits that help decrease stress and aggressive behavior ( K. 1998).

Other options that can be used to reduce Urban Heat Island such as: COOL ROOF Cool roofing can help address the problem problem of heat island , which results in part from the combined heat of numerous individual hot roofs in a city or suburb. Cool roofing product are made of highly reflective and emissive materials that can remain approximately 28-33 oC cooler than traditional materials. Many cool roof products are bright white. These products get their high solar reflectance primarily from reflecting in the visible portion of the spectrum (Gregory Chin, Chin, Andre Desjarlais, Desjarlais, Mauty Estes, Estes, Reducing Uban Uban Heat islands: Compendium of Strategies Cool Roofs 2005 ( http://www.epa.gov/heatisland/mitigation/coolroofs.htm )

COOL PAVEMENT

Cool pavement refer to a range range of established and emerging emerging materials. These pavement pavement technologies tend to store less heat and may have lower surface temperatures compared with conventional products. They They can help addres addresss the problem problem of urban urban heat heat island islands, s, which which result result in part part from from the increase increased d temperatures of paved surface in a city or suburb. Conventional pavements are impervious concrete, which can reach of 48 -67 o C. These surface can transfer heat downward to be be stored in the pavement subsurface, subsurface, where it is re-released as heat at night. The warmer daytime surface as it runs off the pavement into local waterways. These effects contribute to urban heat island and impair water quality ( Bruce Ferguson, kim Fisher, jay golden, Lisa hair, Reducing Urban Heat Island: Compendium of Strategies (http://www.epa.gov/heatisland/mitigation/pavements.htm )

Cool

Pavement

2005

Conclusions

We have become more conscious of the quality of life in our urban areas, but most of this is directed to visual and aesthetic considerations. The role and importance of vegetation in the city especially treed areas, needs much more attention. I had the privilege of speaking at the first Canadian conference on urban forests some years ago, but the concept needs momentum. There is no doubt all towns and cities have modified their climate. The amount varies, but generally the larger the community the greater the change. Society has concerned itself with the forests outside the city limits, but they are probably even more important inside. Vegetation not only modifies the climate and creates areas of cool; it also absorbs  pollution and particles. The more plants of any size we can incorporate into the built up areas the better. Every community should create a department of flora and fauna and establish development strategies that use knowledge about urban climates. A material with high albedo can reduce the solar heat gain during the day time. The surface temperature of the material is lower than that of a material with low albedo. The dark colour material can be up to around 7 0C higher than the ambient air temperature while the lightcolour one is only around 2-3 OC higher than the air temperature.

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by

Sacr Sacram amen ento to’s ’s

Urba Urban n

Fore Forest st..

Jour Journa nall

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