Date of submission: 12
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- 2.1 Research Hypothesis
- 3. Literature Review
- 3.1 Urban Sprawl
Aims and ObjectivesThe primary aim of this paper is to utilise the Landsat archive to investigate urban growth in Austin, Texas over a 22 year period and use a land change model to provide an estimate for future urban growth. This will involve:
2.1 Research HypothesisThe research hypotheses are that the NDVI differencing change detection technique will prove an effective method in measuring urban growth in Austin and it will provide reliable information regarding the amount and location of change. The second main hypothesis is that using the classified maps as an input into the Idrisi Land Change Modeler will yield a realistic and useful prediction of future urban growth in the city. 3. Literature ReviewThis chapter will start with an in depth look into urban sprawl. A review of previous research into urban sprawl will be carried out with an emphasis on the use of remote sensing methods to effectively capture this. Methods of change detection will then be assessed with a focus on the use of the Normalised Difference Vegetation Index in assessing changes in land cover. The final part of this chapter will involve reviewing the use of Land Use/Cover Change models with a focus on the Idrisi Land Change Modeler which has been utilised in this study. 3.1 Urban SprawlWhile the global population has grown dramatically during the last century, we have also witnessed a ‘population implosion’: the unprecedented concentration of people into urban areas around the globe (Masek et al, 2000). Although this trend started within cities in Europe and North America it is now very much a global phenomenon, with cities in developing nations growing at rapid rates (Kraas, 2007). Although a consensus on a definition for urban sprawl has not been reached it is generally characterised by scattered and uncontrolled development on the urban periphery. Urban growth was long considered a sign of regional economic vitality (Yuan et al, 2005); however it has now become a major concern in many areas around the world (Xian and Crane, 2005). Although cities must grow spatially to accommodate an expanding population, the claim is that often too much spatial growth occurs. This excessive growth can cause a number of issues and urban sprawl has become a particular problem throughout the United States (Xian and Crane, 2005). Downs (1998) notes that “suburban sprawl has been the dominant form of metropolitan area growth in the US since the 1950’s”. Figure 1: Urban sprawl in Melbourne, Australia. Source Wikimedia Commons 
There are a number of causes of urban sprawl and it can be considered to be the outcome of a complex array of factors including technology, local geography, economics and politics that interact in a number of different ways (Nechyba and Walsh, 2004). Bruekner (2000) argues that sprawl is stimulated by three main forces – a growing population, rising incomes and falling commuting costs. Squires (2002) suggests that the development of modern private transport has undoubtedly facilitated urban sprawl but other political, economic and social factors need to be considered, including the globalisation of the economy and subsequent decentralisation of jobs from traditional Central Business District (CBD) areas. Rusk (1999) notes that longer-term mortgages, coupled with subsidised mortgage insurance has made home ownership open to more households than ever before and Squires (2002) notes that families will choose to live in communities that offer the most attractive package of services that they can afford. Schools, crime rates, access to shops, transport links and the environment will all be considered by families deciding upon a location and these are frequently perceived to be better in a suburban environment. Nechyba and Walsh (2004) believe there is a pull of people out of central cities because of attractive features of suburbs and also a push of people out of central cities because of inner city problems. Geller (2003) notes that for many, the great American Dream is associated with large, single-family homes, lots of land and a feeling of independence. Urban sprawl does provide this low density lifestyle and also a separation from some of the social problems that may be experienced in the inner city. For many, living in suburbanised areas will have marked a vastly improved quality of life. The increased popularity of larger houses which are more distant from the urban centre has contributed to sprawling cities across the US and indeed also the wider world. The perceived benefits of urban sprawl are increasingly balanced against ecosystem impacts, including loss of green spaces, degradation of air and water quality and a number of socioeconomic effects including economic disparities, social fragmentation and impacts upon health (Squires, 2002). One of the most concrete costs associated is the loss of green spaces. Within and around urban areas, green spaces provide a huge number of benefits and play a crucial role in enhancing the ‘livability’ of cities. Some of the many advantages of urban green spaces include; air and water purification and mitigation of the impact of environmental pollution, regulation of microclimate, a habitat for urban wildlife, recreational, spiritual and therapeutic value as well as social integration (Gairola and Noresla, 2010). Green space improves the environmental quality of life, promotion of public health and can help to foster local sustainable development (Schopfer et al, 2005). Therefore the preservation and maintenance of green spaces is well acknowledged and has become an important policy issue in many cities (Rafiee et al, 2009). The loss and fragmentation of green spaces due to outward urban growth greatly diminishes these benefits noted above. Urban sprawl has also contributed to creating a car dependant society and Frumkin (2002) notes that a number of negative effects of sprawl relate directly to a heavy reliance on cars – including increased air pollution and car crashes causing injuries and fatalities as well as a less active lifestyle. Cars are a leading source of air pollution (Kennedy and Bates, 1989). Nechyba (2004) states that “In the United States in 2001, on-road vehicles accounted for 37% of total nitrogen oxides, which play a major role in the formation of ground-level ozone, particulate matter, haze and acid rain; 27% of volatile organic compounds, which react with nitrogen oxides to form ground-level ozone; and 62% of total emissions of carbon monoxide, which is a particular threat for individuals who suffer from cardiovascular disease”. The link is generally that urban sprawl is associated with high levels of driving, driving contributes to air pollution and air pollution causes increased morbidity and mortality amongst a population. Other negative health impacts of sprawl include an increasingly sedentary lifestyle, with often less exercise being taken due to a reliance on a car. Ewing et al (2008) conducted a study into urban sprawl and health and reports that “residents of sprawling counties were likely to walk less during leisure time, weigh more, and have greater prevalence of hypertension”. There is a body of evidence assessing the health impacts of urban sprawl, in particular links with obesity (Frumkin 2002, Zhao and Kaestner 2010 and Bernell et al 2003) and findings do point towards a sprawling city potentially being a factor in increased obesity rates. The effects of sprawl extend far beyond environmental and health issues and it has been acknowledged that sprawl can contribute to an increasingly uneven and socially fragmented city. Development in the urban periphery often requires huge investments in roads, sewers, schools and other public infrastructure. As new communities are built, new infrastructure needs to expand to accommodate them (Benedict and McMahon, 2002). This growth is believed to reduce the incentive for development of land closer to city centres, contributing to the decay of downtown areas. As a population moves towards the suburbs industry seeks out these outlying communities and the relocation of jobs (often termed ‘job sprawl’) can exacerbate economic disparities within a city (Squires, 2002). Although the process of job sprawl has been debated, a study by Kneebone (2009) highlighted that 95 out of 98 metropolitan areas in the US saw a decrease in the share of jobs in the traditional city centre. Sprawl is also believed to lead to a decrease in community engagement as suburban living is often characterised by a longer commute and segregated and homogenous neighbourhoods. Putnam (2000) estimates that each additional 10 minutes of driving time predicts a 10% decline in civic involvement. Suburban development patterns also tend to lead to economic stratification – many developments are built to specific price ranges which leads to a segregation and whilst this creates income homogeneity within neighbourhoods, it intensifies income inequality across the wider metropolitan area (Frumkin 2002). Collectively, these types of trends suggest that certain features of sprawl can create an increasingly socially fragmented and uneven city. As highlighted above, there are a number of problems associated with urban sprawl. There has been a response to sprawl, which has included the ‘Smart Growth’ movement in the United States. Smart Growth strives to protect farmland and open space, revitalise neighbourhoods, and provide more transportation choices (Geller, 2003). Many places in the U.S. have adopted smart growth initiatives, such as the state of Maryland, which in 1997 provided incentives for brownfield site development whilst denying similar subsidies for projects outside of the target area. In Denver, another city in which the metropolitan area has grown rapidly, a light rail system has been built which connects the suburban area from all directions to the downtown area, and a free shuttle bus runs the length of the downtown spine (Geller, 2003). One of the most controversial measures in combatting sprawl is an Urban Growth Boundary, which is a zoning tool that slows urban growth by banning development in designated areas on the urban fringe (similar to the Greenbelt adopted in the United Kingdom). In 1979, Portland, Oregon created an urban growth boundary. Whilst effective in limiting sprawl it has been argued that this created a number of negative effects, including an increase in housing costs. Geller (2003) notes that whilst there is some debate over opinions on smart growth’s efficacy, it is becoming part of the urban landscape as the debate over the negative impacts created by urban sprawl continue. It is hugely important that urban growth is monitored to develop strategies for sustainable development and to improve the livelihood of a city (Yang, 2002). The ability to monitor urban land cover changes is highly desirable by local communities and policy decision makers alike. The increased availability and improved quality of multi-temporal remote sensing data offers opportunities to monitor urban land cover changes and urban sprawl in a timely and cost-effective way. Download 0.72 Mb. Share with your friends:
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