Thursday, January 29, 2009
My new blogspot would be
Sorry for the inconvenience and hoping you visit my new site.
Sunday, January 25, 2009
Thesis Executive Summary
Pictures of your presentation boards and drawings
Be proud of your work! Share it with others!
The St. Basil's Cathedral is located on the
The cathedral was commissioned by Ivan the Terrible to commemorate the capture of the Khanate of Kazan. In 1588 Tsar Fedor Ivanovich had a chapel added on the eastern side above the grave of Basil Fool for Christ, a Russian Orthodox saint after whom the cathedral was popularly named.
The Hallgrímskirkja (literally, the
4. Temppeliaukio Kirkko: The
Temppeliaukio Kirkko (
5. Cathedral of Brasília: The
The Catedral Metropolitana Nossa Senhora Aparecida in the capital of
The Borgund Stave Church in Lærdal is the best preserved of
7. Las Lajas Cathedral: A
Later on, a mysterious painting of the Virgin Mary carrying a baby was discovered on the wall of the cave. Supposedly, studies of the painting showed no proof of paint or pigments on the rock - instead, when a core sample was taken, it was found that the colors were impregnated in the rock itself to a depth of several feet. Whether true or not, the legend spurred the building of this amazing church.
Located over the Kalemegdan Fortress in Belgrade, Serbia, the Ružica Church is La small chapel decorated with... with trench art! Its chandeliers are entirely made of spent bullet casing, swords, and cannon parts..
The space the church now occupies was used by the Turks as gunpowder storage for over 100 years and it had to be largely rebuilt in 1920 after WWI. Though damaged by bombings there was an upshot to the terrible carnage of The Great War. While fighting alongside
10.Chapel of St-Gildas: Built into the base of a bare rocky cliff
The Chapel of St-Gildas sits upon the bank of the Canal du Blavet in Brittany,
Saturday, January 24, 2009
Speakers will include:
Ms. Tina Paterno, Senior Conservator from New York City
- the Smithfield Church, built in 1925, in Pittsburgh, Pennsylvania,
- the , built in 1876, in Garden City, New York;
Archt. Arnulfo Dado, of the National Museum
- San Agustin Church, Intramuros, Manila, completed in 1607 and declared a by ,
- the Parish Church of San Raymundo de Peñafort, Rizal (Malaueg), Cagayan, built in 1607 and declared a National Cultural Treasure by the NCCA;
Archt. Angel Lazaro, of Angel Lazaro & Associates
- Parish Church of , in Masinloc, Zambales, built in 1607 and declared a National Cultural Treasure by the NCCA.
Lunch will be served. Minimum donation is P 200 for non-members, P 100 for HCS members, and P 50 for undergraduate students. For more information, please contact the HCS at 521-2239 or hcs_secretariat@ yahoo.com.
Thursday, January 22, 2009
Conclusion and Recommendations
While more definitive studies are continuing, it is clear from the data that the built environment, and corresponding lack of vegetation, is several degrees warmer than nearby natural environments. The increasing effects in tropical mega-cities have created increasing concern for the sustainability of the urban system.
Studies in the urban heat environment have gone a long way. Most of the earlier researches though were focused from the meteorological point of view. The motivation was to see the implications of heat island on weather phenomenon. Another group of researchers tried to study heat environment from an architectural point of view, where their intentions were to provide the ambient temperature and comfort condition inside buildings. The former was of concern of regional scale and the latter was of building scale but none approach it from the scale of a city. However, with the advent of remote sensing and aeronautics research using techniques developed for space technologies, a sudden interest is observed.
Recent studies that have used these technologies have focused on the understanding of land use patterns to heat production and its effect on the lowest layers in the atmosphere. The concern is on how the characteristics of the urban landscape drive this urban heat island effect and how urbanization and growth shape the dynamics of the effect. Parks and greenbelts reduce temperatures while the Central Business district (CBD), commercial areas, and even suburban housing tracts are areas of warmer temperatures. Every house, building, and road changes the microclimate around it, contributing to the urban heat islands of our cities. The urban heat island effect will exist as long as urban areas exist. However, the growth of heat islands can be slowed, and its effects reduced.
The purpose of this paper is to shed light on the urban heat environment, their implications to urban sustainability, and to identify measures to alleviate it. There are many possible measures that exist to make cities more sustainable and habitable and urban planners and policy makers should think this phenomenon seriously before the situation gets worse further. In some affluent cities such as
Akbari, H. 1998. “Cool Roofs Save Energy” ASHRAE proceedings, January.
Luvall, Dr. Jeffrey C and Dr. Dale Quattrochi. "Whats hot in
Heat Island Group "Air Quality"
NASA "NASA Satellite Confirms Urban Heat Islands Increase Rainfall Around Cities"
“Urban Climate Modifications”
Wolman, Abel, (1965). quoted by, White, R. & J. Whitney, (1992). "Cities and the Environment: An Overview". In, Stren, R., R. White & J. Whitney, (eds.), Sustainable Cities: Urbanization & the Environment in International Perspective, Boulder, CO.: Westview Press. pp. 8-51.
Rohinton Emmanuel.“Summertime Urban Heat Island Mitigation: Propositions based on an Investigation of Intra-Urban Air Temperature Variations” Architectural Science Review
Stone, Brian Jr. and Michael O. Rodgers. 2001. Urban Form and Thermal Efficiency: How the Design of Cities Influences the Urban Heat Island Effect . Journal of the American Planning Association 67(2), 186-198.
Cardelino CA, Chameides WL. 1990. Natural hydrocarbons, urbanization, and urban ozone. Journal of Geophysical Research 95 (D9):13971-13979.
Stone, Brian Jr. Urban heat and Air Pollution: An Emerging Role for Planners in the Climate Change Debate. Journal of the American Planning Association , forthcoming.
Stone, Brian Jr. 2004. Paving Over Paradise: How Land Use Regulations Promote Residential Imperviousness . Journal of Landscape and Urban Planning 69, 101-113.
Stone, Brian Jr. 2003. Air Quality by Design: Harnessing the Clean Air Act to Manage Metropolitan Growth . Journal of Planning Education and Research 23, 177-190.
Estes, Maurice Jr.; Gorsevski, Virginia; Russell, Camille; Quattrochi, Dale; and Luvall, Jeffrey. ”The Urban Heat Island Phenomenon and Potential Mitigation Strategies”. 1999 EPA National Planning Conference.
“Here Comes Urban Heat” Science @NASA
Rosenberg, Matt. “Urban Heat Islands: It sure is Hot in the City!”.
“State of Environmental Situation”
Heat Island Mitigation Strategies: The Role of Urban Planning
Till today, urban developers and policy makers are not serious on the implications of the worsening heat environment. The costs as discussed above, are tremendous which would force this effect to be taken seriously into up-coming days. On one hand, there are certain things that might be difficult to change such as urban thermal mass, weather patterns and surface roughness. Elimination of these effects would require complete and drastic new way of thinking in the way cities are built and operate. But on the other hand, there are plenty of corrective measures that can be taken within the existing urban set-up such as increasing vegetation cover, albedo modification, efficient energy consumption and management of heat discharge sources which are possible by supportive urban planning and policy measures.
Increasing vegetative cover
Tree plantation is the most obvious and the easiest way to improve heat environment in existing urban set-ups. Trees help in a number of ways; they provide direct shade to the buildings from solar radiation so that less radiation will reach to the building walls, windows and roof to be absorbed. They also create shades in the soil and concrete pavements to act as heat sink for the buildings and asphalt roads. Increase in water vapor due to evapotranspiration by plant leaves is significant in taking the heat away. Trees also act as pollutants, carbon and noise sink. It helps to mitigate greenhouse effects by consuming carbon dioxide in the photosynthesis process. It is estimated that a street lined with trees can reduce dust particles of about 7,000 particles per liter of air. However, care must be used in choosing the type of trees since some trees give off organic compounds (hydrocarbons) into the atmosphere and contribute to ozone in forming smog.
Planting programs can help reduce urban temperatures and make cities greener. Within ten to fifteen years – the time it takes a tree to grow to a useful size – trees placed in strategic locations can reduce heating and cooling costs by an average of 10-20%. Over their lifetimes, trees can be much less expensive than air conditioners and the energy needed to run them.
Well-distributed green parks and water bodies around the urban city act as recreational and aesthetic beauty. Urban planners are concerned with parks and water bodies but their motivation is for aesthetic beauty rather than betterment of heat environment. In the existing urban set-up, metropolitan authorities could encourage green belts around the roadside and plantations. This strategy depend on the local climate condition whether the place of concern is hot-dry or hot-humid in nature. In the hot-dry regions, the evaporation from the soil is minimal, urban parks and water bodies increase water evaporation from both the plants and the soil, consequently the effect on local climate could be significant and desirable. On the contrary, hot-humid regions have low specific evaporation and reduction in the wind speed near the ground is undesirable from the comfort viewpoint (Givoni, 1997).
Albedo is defined as the ability of the surface to reflect solar radiation. It is different from reflectivity in the sense that reflectivity might only account for visual bands whereas albedo accounts for all the incoming radiation to the surface. It is basically hemispherical reflection of radiation integrated over the solar spectrum (0.3 – 2.5 mm) and includes specular and diffuse reflection (Bretz et al, 1998). Asphalt roads, concrete pavements and corrugated roofs have low values of albedo which form the major part of the dense mega-cities. Low albedo surfaces absorb significant proportion of the solar radiation and contribute in worsening urban heat environment. The mitigation strategy therefore is to improve over-all albedo of the urban surfaces.
Improving the urban albedo, such as for buildings and other surfaces have additional advantages. Apart from facilitating urban surfaces to reflect most of the solar radiation, it also contributes in cooling the buildings so that air-conditioning demand is greatly reduced. Studies have shown that the cooling energy savings from the high-albedo roofs and walls in the buildings are very significant. Any heat island mitigation strategy would be required to identify the opportunities that exist in improving the urban surface albedo. The surface albedo property can be greatly enhanced either by mixing it with some third material that can greatly increase its albedo or replacing the traditional construction material completely. The “cool construction materials” can be used to improve solar reflectance without significant cost additions. The choice of light and white colored surfaces is possible, however, a distinction between the light colored surface and high albedo surface should be well understood since light colored surface only means high reflectivity in the visible band.
The effect of albedo modification by one or combination of various methods at the scale of a city and their implication to the overall temperature is not very much studied. In general, the motivation for such albedo improvement has been observed from the air-conditioning viewpoint at building scale rather than reduction of overall thermal situation at the city scale. Building owners, builders and architects have choice to select color of the rooftops, type of construction materials and other measures. Urban planners and policy makers can change the attitude of the stakeholders by improving building codes with thermal considerations, energy management and appropriate urban planning.
Efficient energy consumption and management of heat discharge sources
Since mega-cities are characterized by high energy consumption, ample opportunities exist to manage energy and the heat discharge sources. As stated earlier, air-conditioning is the major stationary heat discharge sources arising from buildings. Air-conditioning units discharge heat to the urban atmosphere continuously due to the energy consumption inside the buildings in various forms (mainly gas and electricity) and absorbed solar radiation through the building surfaces. Three types of management is important here. First, is to enhance energy efficiencies of the end use appliances and the way of supplying energy. Second, is the energy efficient building design from architecture standpoint. And third, is the location of heat discharge sources. High-rise buildings allow the flexibility of placing the air-conditioning units (or plants) at the height significantly above the ground surfaces and the prevailing wind at the height can effectively swipe away the heat without letting it to concentrate in the urban canopy. Although there could be concern on the costs that would conflict with the optimization of piping, a balance optimum is possible. A mixture of high-rise and medium rise buildings in the dense urban area also enhance the over-all urban ventilation by creating turbulence in wind canopy, the ventilation in such case might be better than the urban area with low density but with buildings of similar heights.
The effect of improving appliance efficiencies in buildings on urban heat environment might be very small without changing the way the energies are supplied into the buildings. A central air-conditioning system is energy and cost-wise more efficient than the smaller units in each rooms or at each floors in the multi-storey structures. District cooling is favorable in the dense urban structure. In individual detached homes, small measures such as shading of air-conditioning units can produce effective results.
Transportation is the major heat discharge source that is mobile and difficult to simulate. It is encouraging that the automobile fuel efficiency is improving but at the same time, concentration of vehicles and traffic congestion is also increasing in the mega-cities and the net effect of which is unfavorable from urban warming standpoint. An exact extent of automobile’s implication on urban heat environment is largely unknown. However, traffic management and reduction in the vehicle idle time in core city areas is expected to greatly relieve the heat island phenomenon.
The anthropogenic heat discharges in the big cities are significant. Major cities in the
In order to combat urban heat island, the air quality has to be improved reducing the level of toxic gases, more trees to be planted, save energy and thus reduce pollution, and thereby save cost of energy and money, and improve the overall livability. Air quality management systems should include abatement and other measures to improve air quality, and to maintain air quality within a defined range. Enacting urban planning legislation to increase the amount of vegetation could see a reduction in temperatures. Another method is to reduce the amount of heat absorbed by civil structures by using construction materials that have high albedo and not prone to heat absorption.
The urban metabolism concept (Wolman, 1965) indicates that environmental quality improvement in urban areas rests on the careful use and removal of energy and matter. In the urban design sense, environment conscious urban designers can use at least three tools for the realization of the goals of energy efficiency, transport reduction and air quality improvement. These are thru zoning laws, building laws, and landscape control. Some attempts at utilizing these tools for the purposes of energy and transportation reduction have already been made (cf. Emmanuel, 1995). Although these attempts are from the temperate climate cities, they offer possible models for hot-humid cities.
In the enhancement of the urban physical environment, quality should be the major goal of climate-conscious design. In order to achieve the design goals of energy efficiency, transportation reduction and air quality improvement, in the tropics, design strategies could take one of the following forms:
Building form guidelines
Activity pattern controls
Control of relationship to natural features
Activity Relationships for Comfortable Moving & Transport Reduction
Provisions for Evening Life (Evenings are tropics' winter).
Pedestrian Paths and Nodes
Network for Cars
Relationship to Natural Features - Landscape Controls
Relationship to Waterbodies
Collection of Rainwater
Measurement of Heat Island
Several techniques are applied to measure heat islands. The importance of these techniques depends upon the nature of requirements. Micro-scale heat island measurements are done by the temperature sensors and some instrumentation which are fairly accurate and well-established. However, in the viewpoint of large-scale measurements such as a mega-city, these are not useful. Site observation with the help of sensors in a mobile source such as a car is one of the important tools to measure heat island effect but is labor intensive and the result difficult to validate due to varying weather conditions each time the observation is done.
Recently, remote sensing technology with the help of satellite images is commonly being used to get information on heat islands. Remote sensing techniques can be used to obtain the thermal images of the place in concern and provide information on land use. Loss of green surfaces, information on surface reflectivity of solar radiation and buildings can be obtained with the help of satellite images. The comparison between past and present date can show the trend of heat island along with land use information which are very important in identifying the degree of severity of heat island phenomenon in a particular place.
There are inherent problems though of remote sensing technology in the planning process. It can provide thermal images but there is difficulty in segregating the types of thermal sources such as from mobile sources or stationary sources. It provides snapshot of situation without any knowledge of the mechanisms that is going on in the urban system. The land use, building and transportation information could be obtained from remote sensing techniques but it is not possible to see their contribution and sensitiveness on the heat island phenomenon.
The information obtained from remote sensing need to be coupled with numerical climatic models in order to analyze the effect of various planning alternatives of land use and heat discharge to improve the urban heat environment. These models are able to study the physical climatic phenomenon in the urban system. In this sense, remote sensing data along with Geographic Information System (GIS) is a powerful tool in providing information to the numerical models which can study, simulate various planning alternatives and can predict the implications on heat environment. Numerical models are the powerful tools to understand the mechanisms of heat island. These models can be validated with site data measurements or from remote sensing techniques.
The following image is an aerial thermal image of a mall and surroundings located in
Although satellite data are very useful for analysis of the urban heat island effect at a coarse level, they do not lend themselves to developing a better understanding of which surfaces across the city contribute to or drive the development of the urban heat island effect. Analysis of thermal energy responses for specific or discrete surfaces typical of the urban landscape (e.g. asphalt, building rooftops, vegetation) requires measurements at a very fine spatial scale (i.e., <15m)>
The explosion of new knowledge on the theoretical aspects of urban climate change is not well matched by practical applications. In particular, urban designers and planners are yet to utilize the current knowledge to develop architectural and urban design strategies for the mitigation of the negative effects of urban heat island. This is in part due to some weaknesses in current methods. For example, some of the problems associated with remote sensing techniques hinder the detection of air temperature heat island that directly affects human comfort as opposed to surface temperature heat island. These problems include, difficulties in "seeing" the vertical active surfaces, the not so well defined coupling of surface and air temperatures in urban areas and inhomogeniety of urban surfaces leading to a patch work of emissivity and albedo. The problem with urban-rural difference method in general is that it assumes weather over time remains constant. Furthermore, the intra-urban differences are ignored. It is pointed out that it is the intra-urban climatic difference that is of value for urban planners and designers interested in mitigating the negative effects of UHIs. In other methods, it is assumed that rural climate is somehow "natural" to the area. However, in the context of rapid global urbanization, there are very few rural areas remaining with their "natural" climates intact.
Typical urban surfaces, such as concrete and asphalt, get much hotter than vegetated surfaces during the day. They store the energy and release it at night, thus creating a dome of warmer air over the city. Hypothesized to result, in part, from the elevated heat capacity and waterproofing effect of urban construction materials, the urban heat island effect is believed to promote ozone formation, increase energy consumption, and exacerbate human and environmental heat stress (Cardelino and Chameides 1990). The increased heat of our cities increases discomfort for everyone, requires an increase in the amount of energy used for cooling purposes, and increases pollution. However, the exact nature of implications depends upon geographical and local climate situation. The major unwanted implications of urban heat island are thermal discomfort, increased cooling demand and air pollution.
Urbanization has a tremendous impact on air quality, both over the city and the surrounding countryside. Air quality attainment becomes a critical problem and is exacerbated by urban growth. We know that usually warm air rises above and leads to the development of a low-pressure area and cold air gushes in. but in cases of urban heat island, the warm air gets trapped in by the weight of the pollutants, which affects the air quality and makes the air heavier to rise.
Urban heat islands and air pollution are closely related in an urban system. Besides discomfort, urban heat islands also heavily contribute to an increase in smog production -- a serious environmental air quality health problem which especially affects breathing for children and seniors. The additional temperature acts as catalyst to enhance photochemical reaction, which increases the particles in the air, and thus contributes to the formation of smog and clouds. The presence of ozone creates smog and is the major environmental problem in many cities around the world. Smog is formed when air pollutants such as nitrogen oxides (NOx) and Volatile Organic Compunds (VOCs) -- mainly coming from cars and power plants -- combine with high outside temperatures, usually during hot summer months. Researchers have co-related that smog event increase by ten percent for each increase of 5˚F in temperature (EPA, 1992). Simply stated, smog formation is directly related to air temperatures -- the higher the air temperature -- the more smog that will be produced. According to the U.S. Department of Energy, a drop in air temperature of just a couple of degrees in urban areas can reduce levels of smog on the order to 5 percent to 10 percent, sometimes up to 20 percent -- by slowing down the cooking rate of smog.
Apart from ozone, some bio-genic hydrocarbons from emissions of automobiles are also expected to increase due to increased temperatures. A significant amount of SOx, NOx, and CO emissions take place from the evaporative losses during tank filling and transportation of petroleum products in the mega-cities.
The UHI effect prolongs and intensifies heat waves in cities, making residents and workers uncomfortable and putting them at increased risk for heat exhaustion and heat stroke. In addition, high concentrations of ground level ozone aggravate respiratory problems such as asthma, putting children and the elderly at particular risk. During periods of extreme heat, even trained athletes have been known to die from heat stroke and/or exhaustion. The extreme temperatures caused by UHIs will undoubtedly place a burden on the country’s healthcare system.
In terms of economic and infrastructure costs, additional cooling energy demand of electricity in commercial and residential buildings during summer is expected to be tremendous. Increased demand for energy can cost consumers and cities thousands of additional money in air-conditioning bills in order to maintain comfort levels. In the city of Los Angeles alone, estimates of up to 100 million dollars are spent on energy each year. The air-conditioning equipments discharge heat (which is derived from electricity produced elsewhere) in the urban atmosphere which ultimately contribute to the raising urban temperature. Further, the air-conditioning demand and outside temperature are very closely related thus requiring additional cooling load. This additional cooling load is again provided by electricity, a large portion of which is wasted as heat to urban atmosphere. Studies have shown that for each degree Fahrenheit the daily average temperature increases, electric power demand increases by nearly two percent (Akbari).
Beyond posing a threat to human health and raising air conditioning costs, the heat island effect can also cause physiological stress in other animals, change the mix of plants and animals that live in the area, and even lead to changes in the distribution of pathogens.
Moreover, added heat in cities can destabilize and change the way air circulates around cities. Rising warm air may help produce clouds that result in more rainfall around urban areas. Mostly during the warmer months, the added heat creates wind circulations and rising air that can produce clouds or enhance existing ones. Under the right conditions, these clouds can evolve into rain-producers or storms.
Modification of the landscape through urbanization alters the natural channeling of energy through the atmospheric, land and water systems. Although large-scale atmospheric and climatic phenomena are global in scope, urban areas cannot be viewed in isolation because the local environment modifies the conditions in the thin air stratum above the ground, generally referred to as the atmospheric boundary layer. As humans alter the natural landscape in the city-building process, the local energy exchanges that take place within the boundary layer are affected. Therefore, modification of the landscape influences the local (microscale), mesoscale, and even the macroscale climate.
Implications in Metro Manila
The worsening heat environment in the mega-cities has created a clear threat to the urban sustainability which is shaded by a surge of international interest in the global warming. The implications mentioned earlier clearly show the importance of improving urban heat environment and their role in ascertaining urban sustainability.
In the past several decades, there has been a worldwide shift from rural to urban areas. In Asia, it was estimated that by the year 2000, the urban population will have grown to 35% of the total population compared to only 21% in 1975. Metropolitan Manila, considered as the 18th largest metropolitan area in the world in 2002, is predicted to reach 25 million by near 2015. The metropolitan region would have to accommodate an increment of 11 million people, 3.5 million in Metro Manila and 7.5 million in the adjoining municipalities. Consequently, Metro Manila will be facing further inflow of populations while the adjoining areas will be facing severe shortage on social infrastructure to cope with the impact of rapid suburbanization.
The rapid growth of Metro Manila poised a tremendous impact on its ecosystem. Its rapid urbanization resulted to congestion and intensification of development activities which:
(1) placed serious strains on supporting structures and rendered existing services inadequate;
(2) resulted to incompatible and conflicting land uses;
(3) encouraged growth on the urban area’s peripheries where basic infrastructure services are not available; and
(4) spoiled the quality of the urban environment
With respect to atmospheric environment, the air quality has deteriorated to a point where people are wondering whether the time has come to wear gas masks. Air quality monitoring stations in eleven strategic locations in Metro Manila showed that the concentration levels of suspended particulate matters, sulfur dioxide and nitrogen oxide are in the up trend. In areas near major thoroughfares, concentration of these three pollutants has already exceeded the levels considered safe by the World Health Organization authorities. Air quality measurements indicate that particulate matter is the overwhelming pollutant of concern followed by lead. Carbon monoxide and nitrogen dioxide levels occasionally exceed accepted standards but particulate mater concentrations consistently exceed the acceptable limits. Emission inventory showed that 70 percent of air pollutants in Metro Manila are attributable to mobile sources (motor vehicles) and 30 percent to stationary sources (industries and power plants).
Due to the presence of high-rise buildings and the concentration of housing and other infrastructures, a phenomenon known as heat island effect is discernible in Metro Manila (See satellite image). This problem is aggravated by the emission of carbon dioxide, a by-product of fossil fuel combustion by both stationary and mobile sources. The presence of carbon dioxide will produce the so called green house effect which is synergistic with the heat island effect causing the ambient temperatures in the area to rise several degrees warmer than the countryside.
A steady increase in mean global temperatures and violent weather over the previous several decades has provided circumstantial evidence that significant changes in global climate are underway (Stone, 1999). Numerous efforts are underway to understand the cause and to explore the technological and management strategies to minimize the implications.
In recent years, the role of human activities in the process of global climate change has attracted a growing level of attention within the scientific community. Perhaps more significant in the short term, however, is the impact human settlement patterns are having on climates at the regional level. Sustainability of human kind is often linked with global climate change but the climate change at city or regional scale is paid little attention by the policy makers and academicians in both the developed and the developing countries. Changing climate in the dense mega-cities around the world is a well-documented phenomenon. Cities like
The Urban Heat Island Phenomenon
“Urban Heat Island” is a climatological phenomenon wherein large urbanized regions have been shown to physically alter their climates in the form of elevated temperatures relative to rural areas at their peripheries. Temperatures of urban areas are usually higher (about 2.5 to 6˚C) than those of its surrounding, and this phenomenon have been reported inside dense and highly urbanized cities around the world.
Heat island effects are severe during the summertime in cities of tropical climate zones. Although the phenomenon had been observed in earlier times in winter time in high latitude cities, mostly in
Figure 1 shows a graph of the temperature versus the level of urbanization. Although most people know that metropolitan areas tend to be hotter than surrounding locations, little is known about the Urban Heat Island (UHI) Phenomenon. Yet the concept has been known for nearly 200 years. The UHI effect was first recorded as early as 1807, when an English scientist named Luke Howard took data in and about
Urban Heat Island Formation
There are many factors to consider in Heat Island Formation. Most importantly, is for a Heat Island to materialize is for an area to become urbanized. Urbanization is considered as prosperity of a country. In the age of modernity, the city economy symbolizes th
e powerhouse of capital accumulation. A city continues to attract entrepreneurship and investment and the clustering of nuclear settlements into urban sprawling.
By year 2025, 80% of the world’s population will live in cities according to a 1999 United Nation’s report. The blue line indicates the trend for the growth of cities. As cities continue to grow, urban sprawl creates unique challenges related to land use planni
ng, transportation, agriculture, housing, pollution, and development. Urban expansion also has measurable impact on environmental process.
Rapid urbanization and population growth in the mega-cities has resulted into massive infrastructure built-up and dense settlements. Urbanization has a dynamic relationship with the physical environment. As cities and urban areas expand (called Sprawl), thousands of hectares in naturally vegetated surfaces are being lost each year -- replaced with asphalt, concrete, rooftops and other man-made materials. While urban growth affects the physical environment (usually negatively), urban environmental changes also affects the qualityof life in these areas. The latter lead to biochemical, epidemiological and psychological responses in the urban dwellers.
Urban Sprawl not only results in the loss of native habitats (where animal and plant species are becoming extinct or endangered), but creates Urban Heat Islands -- where man-made materials such as asphalt store much of the sun's energy producing a dome of elevated air temperatures over the urban area. In urban areas, buildings and paved surfaces have gradually replaced preexisting natural landscapes. As a result, solar energy is absorbed into roads and rooftops, causing the surface temperature of urban structures to become 50-70˚F higher than the ambient temperatures. As surfaces throughout an entire community or city become hotter, overall ambient air temperature increases. This phenomenon can raise air temperature in a city by 2-8˚F (World Meteorological Organization, 1984).
Dr. J. Marshall Shepherd and colleagues at NASA's
Man-made changes to the urban environment have been the traditional sources of the worsening urban heat environment. In the process of urbanization, vegetated land surfaces are converted into concrete and asphalt. These changes in the nature of surface have primarily affected solar reflectivity (popularly called albedo), evaporative efficiency and roughness of the land surfaces. Building density and type, amount of road surface, and energy use, as well as local topography and regional wind patterns, all work together to modify a city’s climate. These causes can be classified according to the following - alterations to urban thermal properties, changes in vegetation cover, heat trapping by urban geometry and man-made (anthropogenic) heat input.
Alterations to urban thermal properties
Today’s urbanized cities comprise asphalt roads, concrete pavements, parking lots, buildings and these absorb, store and radiate more heat than the vegetated surfaces. This disrupts the natural radiation balance of the surface resulting into the warmer city. The urban heat island effect is often noticed at night when buildings and other constructed surfaces radiate the heat they have accumulated during
The most influential property in the formation of urban heat island is that of albedo. Albedo is defined as the ration between the light reflected from a surface and the total light falling upon a surface. As the picture shows, albedo can range greatly. Clearly, the albedo of vegetation is much greater than that of civil structures, resulting in structures absorbing much more solar radiation than trees and plants.
Changes in vegetation cover
Heat islands are created when city growth alters the urban fabric by substituting man-made asphalt roads and tar roofs and other features for forest growth. Apart from radiation balance, vegetation loss is responsible for decreasing evapotranspiration process in which plant uses heat from the air to evaporate water in the leaf transpiration process. The process releases moisture into the atmosphere. This process is similar to sweating in humans, effectively releasing heat into the atmosphere. As the water evaporates from vegetation, heat is taken out of the environment. In that way vegetation act as heat sink. They are also responsible for retaining water into the soil and their absence decrease the ability of the soil to retain water thereby decreasing the evaporation rate. Therefore worsening heat environment is partly responsible for the decreased humidity in mega-cities too. Studies in
Heat trapping by urban geometry
Another important reason for worsening of heat environment is the change in the wind pattern. Urban infrastructures increase surface roughness and they lower wind speeds which could have carried away surface heat gain. The formation of urban canopy changes the wind pattern and does not allow wind to enter or to swipe away from the near ground surface effectively, trapping heat inside the canopy
The canyon structure that tall buildings create enhances warming. During the day, solar energy is trapped by multiple reflections off the buildings while the infrared heat losses are reduced by absorption. The city also changes the overall cooling action of the wind by channeling it into narrow streets. The geometry of high vertical walls and narrow streets also increases the summer heat cities as the high sun is reflected downward and is absorbed, and then reradiated, by the often rocklike street and building surfaces.
Man-made (anthropogenic) heat input
In order for cities to thrive, energy production is a necessity. Great amount of heat is released into the environment by powerplants. Transportation is also contributes large amounts of heat, which is evident to those stuck in rush hour traffic. Clearly, everyday human activity required for a functional society only aggravates the heat island problem. The biggest contributions are from areas of high industrialization, airports and seaports. These areas have enormous energy expenditures, and are highly unlikely to contain vegetation.
Mega-cities are characterized by high population density, high per capita energy consumption and their demand for energy is fulfilled in the physical forms such as electricity, oil, gases and coals which are ultimately discharged as heat into the urban atmosphere. Direct heat discharges are usually categorized as stationary and mobile. Heat discharge from buildings by air conditioning units is the single major source of stationary heat discharge. Although many industrial plants and industries are located far from the cities, still some of them are located in the cities which release heat directly into the urban environment. However they usually discharge heat from tall chimney stacks that are usually easy to swipe away by the wind breeze. Automobiles discharge large amount of heat that is mobile in nature. In the city centers and high traffic zones, the concentration of this discharged heat further increases by congestion and presence of fuel inefficient vehicles. A closer look into a mid-size vehicle for urban driving cycle suggests that nearly thirteen percent of total input energy is converted into the useful work while the rest dissipates as heat.
The cumulative effects of all these factors cause urban environment to be hotter than the surrounding areas. Similar to the effects of global warming, such “urban warming” can have substantial implications for air quality and human health within affected regions Increasing at a rate of 0.25 to 2˚F (0.1 to 1.1˚C) per decade, the heat island effect within the urban cores of rapidly growing metropolitan regions may double within 50 years (McPherson, 1994). In light of the roughly 2.9 billion new residents to arrive in urban regions between 1990 and 2025, there is a pressing need to ascertain the implications of urban warming for metropolitan regions and to identify potential strategies to counteract regional climate change.