Retrieved from: http://www.lternet.edu/research/keyfindings/urban-heat-island-effects
By: Sana Jameel and Daniel Scorpio
2003 European Heat Wave
Natural disasters, such as floods, lightning strikes, tornadoes, and hurricanes have devastated human lives across the world. These types of weather events often make headline news and, depending on the severity of the incident, take extended amounts of time to recover. However, heat waves, on average, take more lives than floods, tornados, hurricanes, and lightning strikes combined (National Oceanic and Atmospheric Administration, n.d). August 2003 was unusually warm for the continent of Europe. A heat wave impacted the region for many weeks, taking approximately 35,000 lives. The most affected by the increased temperatures were the young and the elderly, with heat stroke being the major cause of death. According to Campbell (2009), August 10th was the hottest day of the month with a temperature of 37° C (p. 6). This particularly devastating weather event is attributed to increased global warming (Campbell, 2009, p. 7).
What is The Urban Heat Island Effect?
Although the 2003 European heat wave seems like an extreme example of elevated global temperature, developed worlds are experiencing similar warming trends in a number of cities known as the urban heat island effect. As stated by the Environmental Protection Agency (2003), the urban heat island effect is the phenomena that urban settings are becoming increasingly warmer than their surrounding rural areas. Atmospheric temperatures in cities experiencing an urban heat island can be as much as 5.6° C warmer than their rural counterparts (p. 2). This occurs because there are large amounts of grey spaces when compared to the scant amount green spaces in cities. Unlike vegetation and trees, which transfer heat into energy and provide shade to surfaces, structurally developed areas absorb heat to only slowly release it later in the day. When solar radiation reaches the surface of an urban environment during the day, the heat is more readily absorbed by pavement, building walls, and rooftops. At night, the heat is slowly released from the materials that absorbed it during the day, warming the urban atmosphere as well. On the contrary, rural landscapes with more green space, are able to reflect more sunlight back into the atmosphere or use the solar energy for photosynthesis, turning the heat into energy and allowing the area to remain relatively cooler (Environmental Protection Agency, 2003, p. 2). As the Environmental Protection Agency (2003) explains, the urban heat island effect poses a public health issue because, as the European heat wave of 2003
demonstrated, above average temperatures increase heat-related health stressors and mortality rates for the most susceptible populations (p. 2).
Retrieved from: http://www.southwesturbanhydrology.com/urbanization-concerns/urban-heat-island-effect/
Urban Heat Island Effect in Los Angeles, California
Los Angeles, California, a highly urbanized district with a population of 3.858 million, is experiencing the urban heat island effect at a rapid rate (United States Census Bureau, 2013). According to the EnvironmentLA (2014) organization, scientific observations show a 2° C – 10° C increase in Los Angeles temperatures when compared to nearby areas (para. 1). This elevated temperature is attributable to rapid population growth and the replacement of green space with urban infrastructure, such as roads and buildings (EnvironmentLA, 2014, para. 2). Los Angeles covers a land area of 1,213.86 square kilometers, where only 63.576114 square kilometers are dedicated to city parks and another 88.12 square kilometers are covered by water. Asphalt covered roads stretch over another 5,840 miles of space over the city, leaving the rest of the area to be dominated by buildings and other infrastructure (Los Angeles Almanac, 2014, para. 1). With such an extreme gap between natural land cover and developed area, it is no wonder that Los Angeles is experiencing such an intense urban heat island effect.
Los Angeles’ Urban Heat Island: A Public Health Concern
An exacerbated urban heat island in Los Angeles paves the way for an increasing public health threat in the area. The Environmental Protection Agency (2003) demonstrates how elevated urban temperatures affect human populations by explaining that extreme hot weather events result in increased instances of heat related physiological stress (p. 2). On average, Los Angeles is a fairly warm region with average summer temperatures reaching 28° C (Weather Channel, 2012, table 1). However, summer temperatures often exceed the average, such as the record high of 45° C during September 2012 (The Weather Channel, 2012, table 1). According to a study in Hong Kong, conducted by Wong, Padden, and Jimenez (2012), a 4.1% increase in the death rate was observed when “average temperature rose 1.0 °C above 29.0 °C for a specific day” (p. 2). These same increases in heat related mortality are possible for the Los Angeles area, especially when there have been observed temperature increases at a greater degree. Looking at the record high temperature of Los Angeles, the Centers for Disease Control (2010) predicted that heat related deaths in Los Angeles could increase 7-fold as the urban heat island effect is exacerbated (para. 1).
Also, Los Angeles’ infamous smog is worsened by the urban heat island effect, resulting in adverse air quality causing diminished cardiovascular health and lung function for the affected (EnvironmentLA, 2014). Smog occurs when elevated levels of pollution are trapped within an area due to air inversion, which is when a layer of warm air sits on top of a layer of cool air, deviating from the normal (South Coast Air Quality Management District, 2012). Studies researching the air quality levels in southern California have shown that persons who “experience numerous days of unhealthful air, had more symptoms of respiratory diseases such as bronchitis and asthma, while the residents of [less polluted areas] had measurably fewer symptoms of those illness” (South Coast Air Quality Management District, 2012, bullet 6). In order to combat an intensifying heat island effect for the Los Angeles area, we propose that the overall albedo of the city be increased by convincing Los Angeles’ city and building council of the cost effectiveness of retrofits in relation to public health and infrastructure.
What is Albedo?
Albedo refers to the solar reflectivity of a surface. Surfaces with a higher albedo are more able to reflect incoming sunlight back into the atmosphere rather than absorb it. Albedo is measured on a scale from 0 to 1 where 0 albedo means no solar radiation is reflected off the surface and 1 means 100% is reflected (ECOCEM, n.d, para. 1) When only looking at terrestrial factors, snow and ice have high albedos, close to 1, whereas wet soils have very low albedo. This is because surface albedo increases as the color of the surface gets lighter. When comparing albedos of different man-made surfaces, lighter pavements and building materials have a higher albedo, therefore making them more reflective, compared to black asphalts.
Retrieved from: http://en.wikipedia.org/wiki/Portal:Global_warming/Selected_article
Cool Pavements
Dark, rough, and low emissivity surfaces with low albedo can be seen all over the Los Angeles landscape. Black asphalt, heat retaining bricks, and dark roofs are evident throughout the entire city, exacerbating the warming effect. The implementation of cool pavements into the Los Angeles landscape could greatly increase the city’s albedo, in turn combatting the urban heat island effect. A study done by Santamouris (2013) shows that one way to introduce cool pavements into an urban landscape is to paint them a lighter color than black. He explains that off white pavements with an albedo of .45 are roughly 12 K cooler when compared to the maximum surface temperatures of black asphalts with albedos of about 0.03 (p. 227) He also explains that a study done in Athens demonstrated PVC pavements to be more reflective than conventional asphalts. When compared to typical concrete pavements, they were 3-5 K cooler (Santamouris, 2013, p. 228). According to Los Angeles’ Bureau of Street Services, there are “6,500 centerline miles of street and 800 miles of alleys” in the city (Resurfacing and Reconstruction Division, 2014). With such a vast amount of pavement in Los Angeles, the implementation of cool pavements could greatly reverse the urban heat island effect, consequentially reducing public health risks for the city. As Taha (1997) points out, “localized afternoon air temperatures on summer days can be lowered as much as 4° C by changing the surface albedo from .20 to .40 in a typical mid-latitude warm climate” (p. 101). This is a practical retrofit to roads because their constant visibility renders them aesthetically impossible to paint pure white. However, a pavement with an albedo of .40 would be painted a much more pleasing light grey or off-white, much
like an old road that hasn’t been repaved in a long time.
Retrofitting existing buildings in the excessively developed Los Angeles area is also another way to fight the urban heat island effect. White roofs could be painted on every roof in the city in order to immensely increase the overall albedo of the region. Similar to the concept of increasing the albedo of city pavements, white roofs have the potential to cool the atmosphere of Los Angeles by reflecting more sunlight back into space instead of absorbing it during the day and releasing it at night. Roofs are also hidden from view which makes painting a bright, white roof more feasible than painting white pavements (Environmental Protection Agency, n.d, p.3).
There are many different ways to implement a cool roof on a variety of building types. There are essentially two types of roofs, low-sloped and steep-sloped, each of which are constructed by different materials. Low-sloped roofs, which are usually found on commercial, industrial, warehouse, multi-family, and retail facilities, are constructed using built-up roofing or a membrane. For these types of roofs, the most viable cool roof retrofit would involve coatings and installation of single-ply membranes (Environmental Protection Agency, n.d, p. 5). According to the Environmental Protection Agency (n.d) coatings typically have albedos of .65, making them effective reflectors (p. 5). Single-ply membranes are adding to low-sloped roofs when they are in need of minor repair. This gives incentive for the building owner to do the repair while also increasing the solar reflectivity of the infrastructure (Environmental Protection Agency, n.d, p.5). Cool roofing for steep-sloped roofs is seeing a steady increase in demand. Painting a steep-sloped roof colors lighter than asphalt, the material mostly used for these types of roofs, results in a more reflective rooftop. Depending on the color and it’s specific albedo, steep-sloped cool roofs are potentially 25% to 65% reflective of solar radiation (Environmental Protection Agency, n.d, p.7). A case-study that implemented cool roofs on 50% of New York buildings simulated a city-wide temperature reduction ranging from 0.7° C to 1.4° C (Environmental Protection Agency, n.d, p. 5). By quantifying the temperature reductions that have been identified using cool pavements and roofs in other cities, Los Angeles could see an atmospheric temperature decrease of about 4.7° C to 5.4° C through the same retrofits to its surfaces.
Retrieved from: http://www.greeninnovationscfl.com/coolroofcoatings.htmImplementation and Resistance
Implementation of cool roofs and pavements to the Los Angeles area must be done through the city’s Zoning and Building Codes. This same audience would also represent our resistance. Our proposal to the Los Angeles city council would stress the cost benefit and public health improvements of diminishing the area’s urban heat island effect.
As stated previously, if Los Angeles continues experiencing an exacerbated urban heat island effect, the amount of heat related deaths in the area could increase approximately 7-fold. Our proposal to incorporate cool roofs and pavements to the city would stress that these retrofits will improve Los Angeles’ air quality while also reducing the amounts of heat-related illness among its citizens. As the Environmental Protection Agency pointed out, energy use increases with elevating temperature, usually through the use of air conditioners. With more energy being used, more fossil fuels are burned, and more pollutants are emitted. It is important for Los Angeles’ city, building, and zoning boards to realize the necessity of reducing the amount of pollutants in the city, therefore reducing LA’s smog (Environmental Protection Agency, n.d, p. 11).
Our proposal would also exemplify the improvements to human health and comfort by reducing the urban heat island effect through cool roofs and pavements. Wong et al. (2013) proved that only a 1 degree C increase in Hong Kong temperatures caused heat related mortality to increase by 4% (p. 2) However, if temperatures start to decrease from the elevated, many lives could be saved, especially those who are the most susceptible to heat related illness. A cool roof program in Philadelphia demonstrated a 1.3° C decrease for indoor air temperature, which greatly improved the lives of the building’s occupants, especially on 35° C days (Environmental Protection Agency, n.d, p.11).
Although a positive environmental impact and effect on human health could result from increasing the albedo of Los Angeles, and therefore reducing the urban heat island effect, there could be opposition to these proposals by the Los Angeles City Council and Building Council. They may first argue that such an extensive effort over such a large area could cost a massive amount of tax payers’ dollars while having a small pay off. However, we predict that the funding for this project would mostly come from the savings it incurs. Knowlton (2011) presents data that shows heat-related expenses due to stress and mortality caused by heat waves from 2002 to 2009 cost the United States roughly 5.4 billion dollars (p. 2). There are also cost savings associated with the decreased energy demand as a result of cooler buildings, as shown in table 1. By spending the money to retrofit Los Angeles and reduce the heat island effect, there could be massive savings in health care and energy usage. Also, the resistant audience may be concerned with the aesthetic look of Los Angeles with different colored pavements and rooftops. I agree that a completely white city would be blinding, but increasing albedo does not necessarily mean using pure white surfaces. Surfaces lighter than black still have a higher albedo, therefore causing a reduction in the heating trend. However, roofs cannot be seen from ground level and they could be painted white for maximum reflectivity.
Table 1. Retrieved from: http://www.epa.gov/heatisland/resources/pdf/CoolRoofsCompendium.pdf
Conclusion
As global temperatures increase, the world’s more developed areas will experience the worst of the change. As we have seen, this is no exception for the Los Angeles area. With an elevating urban heat island effect and its subsequent health impacts, reducing the effect is crucial. Although there are many different ways in which Los Angeles can become more sustainable, the implementation of cool roofs and pavements gives the greatest reward. The program can essentially be self-funded, cause a significant decrease in temperature in a short amount of time, and provide better quality of health to the Los Angeles citizens.
References
Campbell, S. (2009). 2003 European heat wave. 1-10. Retrieved from: http://www.atmos.washington.edu/2009Q1/111/ATMS111%20Presentations/Folder%201/CampbellS.pdf
Centers for Disease Control and Prevention (November 29, 2010). Heat-related morbidity and mortality. National Center for Environmental Health. Retreived from: http://www.cdc.gov/climateandhealth/effects/heat_related.htm
ECOCEM (n.d). The albedo effect. Retrieved from: http://www.ecocem.ie/environmental,albedo.htm
Environment LA (2014). Urban heat islands/cool communities. EnvironmentLA Sanitation, City of Los Angeles. Retrieved from: http://environmentla.org/programs/urbanheatislands.htm
Knowlton, K. (November, 2011). Health and climate change: Accounting for costs. National Resources defense council, 1-4. Retrieved from: http://www.nrdc.org/health/accountingforcosts/files/accountingcosts.pdf
Los Angeles Almanac (2014). City of Los Angeles. Retrived from: http://www.laalmanac.com/LA/index.htm
Los Angeles Almanac (2014). Parks in the city of Los Angeles. Retreived from: http://www.laalmanac.com/parks/pa12.htm
National Oceanic and Atmospheric Administration (n.d). Heat wave: A major summer killer. United States Department of Commerce. Retrieved from: http://www.noaawatch.gov/themes/heat.php
Resurfacing and Reconstruction Division (2014). Welcome to resurfacing and reconstruction! Bureau of Street Services. Retrieved from: http://bss.lacity.org/resurfacing/
Santamouris, M. (2013). Using cool pavements as a mitigation strategy to fight urban heat island – A review of the actual developments. Renewable and Sustainable Energy Reviews, 26, 224-240. DOI: http://dx.doi.org/10.1016/j.rser.2013.05.047
South Coast Air Quality Management District (September 11, 2012). Smog and health. Retrieved from: http://www.aqmd.gov/smog/historical/smog_and_health.htm#Sources of Smog
Taha, H. (n.d). Urban climates and heat islands: Albedo, evapotranspiration, and anthropogenic heat. Energy and Buildings, 25, 99-103. Retrieved from: http://www.javeriana.edu.co/arquidis/educacion_continua/documents/Urbanclimates.pdf
United States Environmental Protection Agency (September, 2003). Cooling summertime temperatures: Strategies to reduce urban heat islands, 1-6. United States Environmental Protection Agency. Retrieved from: http://permanent.access.gpo.gov/LPS111993/LPS111993_HIRIbrochure.pdf
United States Environmental Protection Agency (n.d). Reducing urban heat islands: Compendium of strategies, 1-31. Climate Protection Partnership Division. Retrieved from: http://www.epa.gov/heatisland/resources/pdf/CoolRoofsCompendium.pdf
United States Census Bureau (November 25, 2013). Los Angeles region. United States Department of Commerce. Retrieved from: https://www.census.gov/regions/los_angeles/
Weather Channel (2012). Monthly averages for Los Angeles, CA. The Weather Channel. Retreived from: http://www.weather.com/weather/wxclimatology/monthly/90089
Wong, K. V., Paddon, A., & Jimenez, A. (2012). Review of world urban heat islands: Many linked to increased mortality. Journal of Energy Resources Technology, 135(2), 1-11. DOI: 10.1115/1.4023176
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