Sustainable Cities: Urban Heat Island
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1. Urban areas experience higher temperatures than surrounding rural areas, forming an "urban heat island" effect. This is caused by urban land use and surfaces like concrete and asphalt that absorb and retain heat. 2. The urban heat island effect can increase city temperatures by up to 10 degrees Fahrenheit and poses negative impacts like increased energy consumption and air pollution emissions. It also exacerbates heat-related health issues. 3. Mitigation strategies include increasing urban green spaces through parks, trees, and green roofs, which disrupt high temperatures. Reflective and cool roof surfaces also help reduce temperatures. However, financial costs and legal restrictions can pose challenges to widespread mitigation efforts.
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Sustainable Cities: Urban Heat Island
- 1. PLAN 1900: Sustainable Cities Week 13: Urban Heat Island Effect Anuradha Mukherji Assistant Professor of Urban and Regional Planning
- 2. GLOBAL TRENDS • From 1804 to 2010, one billion to almost seven billion • Global population in urban center up from 3 to 50 percent by 2010 • Number of cities growing, 86 cities in 1950 with a population of 1 million, today its 400 cities • Urbanization rates highest in the Global South • Regardless of population and spatial size, urbanization alters the local climate system
- 3. URBAN HEAT ISLAND (UHI) EFFECT • Urban regions become warmer than their rural surroundings forming an ‘island’ of higher temperatures in the landscape • UHI is usually measured by the difference in temperatures between urban and rural areas • The highest difference is usually found at the urban core – e.g., downtown. • Elevated temperatures can also be found in areas with urban land-use categories (i.e., commercial, residential) • Parks, lakes, and open areas in a city observe lower temperatures than the surrounding urban area
- 4. Keywords: Thermal admittance: the ability of surface to store and release heat (concrete and asphalt ↑) Albedo: The percent of incoming solar radiation that is reflected back to space (light surfaces such as snow and ice ↑ - 80-95 %, dark- colored materials such as asphalt ↓ 5-10%) Urban canyons: an artificial ‘canyon’ formed by two vertical walls of buildings with a horizontal streets or pavement surface sky view factor (SVF); the fraction of sky seen” from a point on the ground up (0=completely obscured, 1 = completely visible) Park cool island (PCI): zones in the urban landscape with relatively cooler temperature due to parks, lakes, or open spaces.
- 5. Urban canyon SVF (sky view factor)
- 6. This image is attributed to NOAA @ 2011 (PD-USGov-NOAA)
- 7. New York – Summer Day Infrared Satellite Image Left: Thermal Data Below: Vegetation Data This image is attributed to NASA @ 2002 (PD-USGov-NASA)
- 8. KEY FACTORS CAUSING UHI • Land use cover and land use change (LULC) – the conversion of earth’s natural surfaces (i.e., grasses, shrubs, trees, bare soil) into urban surface (i.e., asphalt, concrete, buildings, glass) for human socio-economic activities • Generation of anthropogenic waste heat (i.e., emissions from factories and transportation systems)
- 9. TYPES OF UHI • Heat islands occur on the surface and in the atmosphere • On hot sunny day, exposed urban surfaces such as roof and pavement are hotter than the air • Surface urban heat islands are present day and night but are strongest during day when the sun is shining • In contrast, atmospheric urban heat islands are weak during late morning and through the day, and become pronounced after sunset due to slow release of heat from urban infrastructure
- 10. This image is attributed to EPA (http://www.epa.gov/heatisland/about/index.htm) Surface & Air UHI
- 11. "Atlanta thermal" by Original uploader was Ryanjo at en.wikipedia - Transferred from en.wikipedia; transferred to Commons by User:Frokor using CommonsHelper.. Licensed under Public domain via Wikimedia Commons Atlanta, Temperature Distribution Top: Temperature rises by 10- 12 degrees during day Right: High daytime temperatures keep city warm at night
- 12. UHI – WHY AN ISSUE While some UHI impacts are positive, such as longer plant- growing season, most impacts are negative: 1. Increased energy consumption: Higher temperatures in summer increase energy demand for cooling and add pressure to the electric grid during peak demand periods. 2. Elevated emissions of air pollutants & GHGs: Increase in energy demand results in more emissions from power plants and heat release from AC units. Higher air temperatures promote ground-level ozone formation 3. Impact on human health: Higher air pollution can cause respiratory issues. High temperatures can contribute to heat cramps, exhaustion, and heat stroke (1995 Chicago)
- 13. MITIGATION STRATEGIES 1. Reducing GHGs through policies to reduce energy use among commercial, residential, and transportation systems through programs such as LEEDS (Leadership in Energy and Environmental) or alternative energy systems 2. Green spaces (i.e., parks, water bodies) can disrupt urban temperature peaks and are called Park Cool Island (PCI) • Urban forests: Increasing tree and vegetative cover • Creating green roofs (i.e., rooftop gardens or eco-roofs) • Installing cool (i.e., reflective) roofs • Using cool pavements
- 14. This image is attributed to "Green City" by Alyson Hurt from Alexandria, Va., USA - Flickr. Licensed under Creative Commons Attribution 2.0 via Wikimedia Commons Rooftop Garden, Manhattan, New York
- 15. This image is attributed to "20080708 Chicago City Hall Green Roof" by TonyTheTiger - I created this work entirely by myself. --TonyTheTiger. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons Rooftop Garden, City Hall, Chicago
- 16. UHI – MITIGATION CHALLENGES 1. Requires financial investment that might not be feasible for individual homeowners or public officials. 2. Individual homeowners bound by covenants, codes and restrictions (CCRs) governing a community or neighborhood and enforced by Homeowners Associations. Mitigation actions might violate CCRs. 3. Conducting cost-benefit analysis – Increase green space need to be evaluated against costs, i.e., the benefit of urban forests vs increase in pollen (allergies) or benefits of parks vs greater demand on water. 4. Mitigation strategies have to be considered within the context of resources and constraints of a given city.
Editor's Notes
- Hazard mitigation implementation measures are broadly categorized into two groups in the literature. One, structural mitigation (e.g. flood control works, engineered defense systems) that seek hazard resistance, and second, non-structural mitigation (e.g. land-use planning and management, development regulations, enforcement of building codes and standards, land and property acquisition, capital improvements for critical public infrastructure, taxation and fiscal policies, and information dissemination) that seek local resilience to hazards (e.g. Berke 1998; Birkland et al. 2003; Cheong 2011; Mileti 1999; Godschalk et al. 2000, 1999; Godschalk & Norton 1998; Thampapillai & Musgrave 1985). Despite an extensive and growing scholarship on hazard mitigation as a critical component of disaster resilience, our understanding of hazard mitigation plan implementation at the local level (e.g. county, municipality) remains limited. Indeed, research on the implementation of hazard mitigation plans at the local level is largely absent from the hazard mitigation and planning literatures. Current literature focuses mainly on mitigation policies (e.g. Birkland et al. 2003; Brody et al. 2009; Burby 2006, 1999; Deyle, Chapin & Baker 2008; Godschalk et al. 1999), the mitigation planning process (e.g. Brody et al. 2007; Kartez & Lindell 2011), and evaluation of mitigation plan quality (e.g. Berke, Smith & Lyles 2010, 2009; Lyles, Berke & Smith 2014). There is little research that focuses solely on the implementation of mitigation plans subsequent to plan adoption (Brody & Highfield 2005, 159). While local governments are increasingly bearing the responsibility of hazard mitigation implementation in their jurisdictions (Brody, Kang & Bernhardt 2010; Faber 1996; Godschalk et al. 1999, Godschalk 2003), it is uncertain whether local governments have the commitment and capacity to prepare mitigation plans and carry out mitigations projects and actions aimed at building resilient communities (Clary 1985; Godschalk et al. 1999; Petak 1984). While implementation happens mostly at the local level (e.g. county, municipality), studies that examine hazard mitigation plan implementation at the local levels are scant (e.g. Brody, Kang & Bernhardt 2010; Godschalk et al. 1999). Additionally, policy implementation scholarship shows that implementation is rarely considered in the design of policy, as the general assumption is that implementation naturally follows policy adoption (O’Toole 2000; Myrtle 1983), which in turn leads to implementation gaps (Schofield 2004). Few studies consider whether the policies and plans are actually implemented subsequent to its adoption (Brody, Kang & Bernhardt 2010; Talen 1996a, 1996b) creating a critical gap in the literature on this vital sub-topic in the field of hazard mitigation. Scholars have identified a number of variables that can influence hazard mitigation plan implementation, which include political commitment (e.g. Burby & May 1998; Webler et al 2003), inter-governmental co-ordination (e.g. Burby & May 1998), public stakeholder participation (e.g. Stevens, Berke & Song 2010; Godschalk, Brody & Burby 2003; Godschalk et al 1999), commitment to evaluation (e.g. Brody and Highfield 2005), organizational capacity (e.g. Brody, Kang & Bernhardt 2010; Godschalk et al 1999), and the role of planners (e.g. Stevens 2010). While these studies are significant, they remain discrete. Comprehensive approaches that model how the aforementioned aspects conceptually and collectively influence hazard mitigation plan implementation are absent in the current literature. The implementation of local mitigation plans can be best understood through place-based studies as it can “offer an in-depth knowledge of local conditions specifically regarding the level of implementation of hazard mitigation…and shed light on important trade-offs and synergies”. Yet, place-based studies (e.g. Godschalk et al.1999) remain largely absent among current approaches that examine hazard mitigation plan implementation.