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Contents: Impacts of Urbanization - Understanding the Affected Environment - Environmentally Sensitive Areas - Land Suitability Analysis - Conclusion - References
The Southwest is one of the most rapidly urbanizing regions of the United States. As a result, evaluating the consequences of urbanization in this arid environment is an important topic. Richard Forman observed, "virtually all great questions of our time involve land" (1995, p.3). This paper addresses how urbanization impacts the land, specifically the landscapes of the Sonoran Desert Ecosystem, and is organized in four parts. In the first part, the impacts of urbanization on the Sonoran Desert ecosystem are summarized. The second part addresses the major biophysical elements which should be considered when making an environmental impact assessment. The third part covers the identification of environmentally sensitive areas. The final section considers methods for determining land-use suitability. Throughout the paper, the Desert View Tri-Villages area of Phoenix, Arizona, will be used as an example. top
The northern portion of Phoenix includes a 110-square-mile planning area known as Desert View Tri-Villages (formerly Peripheral Areas C and D) (Figures 1 and 2). This planning area, with its current population of 7,950 residents, has recently come under intense development pressure, with between 250,000 and 350,000 new residents expected in the next 45 years.1
The southern border of Desert View Tri-Villages is delimited by the Central Arizona Project (CAP) canal, which brings water from the Colorado River on Arizona's western border to central and southern Arizona. This canal forms a physical barrier, inhibiting Phoenix's development to the north. Until recently, the city has delayed providing infrastructure to this relatively remote area. While the area south of the canal has experienced rapid suburban growth, the area north of the canal has remained largely undeveloped and has retained a rural character.
Desert View Tri-Villages abuts the city of Scottsdale on the east and the towns of Cave Creek and Carefree on the northeast. To the northwest, the rural community of New River is the future site of a planned community of 10,400 people by the year 2020 (Ostler 1995). The areas to the east and north are also facing intense development pressures and also have similar, natural desert environments. top
In the planning area itself, the Sonoran desert landscape is being transformed by a number of new residential communities and commercial centers, with more in the zoning approval and construction backlogs. Major, new residential communities include Tatum Ranch, where 3,400 dwelling units (DU) will be built on 1,400 acres for a gross residential density of 2.4 DU per acre, and Desert Ridge, whose 5,700-acre, 25,000-home development will lead to a gross residential density of 4.4 DU per acre (Northeast Phoenix Partners 1995). Construction is almost complete on Sumitomo-Sitix's six-billion-dollar silicon wafer manufacturing plant in the southeastern part of the planning area.
Ortolano (1984) has summarized some of the negative environmental effects of residential and commercial development (Table 1: Some adverse environmental effects of residential and commercial development). These effects, and others, are evident in the urbanization occurring in the Sonoran desert region. In the north Phoenix metropolitan areas three impacts are especially pronounced: the loss of native plant and animal species, the disruption of the natural wash drainage system, and the decline of visual quality. In addition, changing land use in north Phoenix as well as other rapidly growing regions in the Southwest is affecting the microclimate (and perhaps larger scale climatic systems too). top
Until relatively recently, the majority of the development in the Phoenix metropolitan region has occurred in the wide, relatively flat alluvial valleys. The Hohokam originally irrigated these lands from 300 to 1450 A.D. when they "disappeared." American settlers rediscovered the canals of the Hohokam and redeveloped the valley for agriculture. Since the second world war, agriculture has given way to suburbanization. The native plants and animals had long been disturbed in the valleys.
More recently, the suburbanization has increased in upland areas where the lower Sonoran vegetation gives way to the more dramatic upper Sonoran vegetation. Plants which give this region its identity, like the saguaro, are lost in the process. Many new developments "blade" large areas and "grub" indigenous plants. Obviously, as their habitat is destroyed, so too are the wildlife. Although there are some efforts to protect native plants, these undertakings cannot keep pace with the rate of development.
Like the vegetation, the hydrology also changes from the valleys to the uplands. The valleys are cris-crossed by canals to the point where little natural drainage exists. When rain comes to the Sonoran desert, it is intense. Significant amounts fall in relatively brief periods. Flash floods result. These floods affect both the valleys and the uplands. top
Alluvial fans occur in the uplands in north Phoenix and north Scottsdale between the mountains and valleys. New developments are disrupting the wash systems, the arroyos, in these alluvial fan areas. New development results in more impervious surfaces which increases the runoff and adds to flooding problems.
The upper Sonoran desert areas of north Phoenix and north Scottsdale are visually spectacular. They have attracted hordes of tourists and have been the location of countless Hollywood movies, television Westerns, commercials for television, and advertisements for magazines. This beauty is being rapidly lost. Americans have seemingly become immune to the ugliness that surrounds us. Breath-taking landscapes such as the upper Sonoran have been converted into endless expanses of visual banality. top
The Phoenix region is hot and getting hotter. As a result of the "urban heat island effect," the average nighttime temperature has increase 3.9° F since 1970 while afternoon temperatures have risen by approximately 1.1° F (Balling and Brazel 1987). Balling and Brazel observe,
The development of an urban heat island has led to an increase in local temperatures. Maximum and minimum temperatures are rising in every month of the year, but the already painfully hot summer months are showing the biggest increases. Night-time temperatures in the three summer months (June, July, August) have shot upward almost 8EF (4.4° C) between 1948 and 1984; June's nightly temperature has risen more than 10° F (5.6° C) during the period of rapid urbanization. There can be no question that the heat island' effect is changing the desert environment (1986, p. 89).
Lougeay et al. (1996) have estimated the radiative surface temperatures for various land uses in the Phoenix metropolitan area (Table 2: Radiative surface tempreatures (10:00 AM) and areal coverage, June 24, 1994, Phoenix, Arizona). They have found irrigated agriculture to have one of the "cooler" surface temperatures. They observe that over one half of the land-use change in recent years has been from agriculture to urban "converting one of the coolest categories of land cover to much hotter categories of land use" (Lougeay et al. 1996, pp. 87-88). They continue, "much of the irrigated agricultural acreage is being affected. This has the effect of warming of the earth's surface, and near surface air temperature, in the metropolitan area as a function of land-use development, perhaps producing a daytime metropolitan temperature field much closer to that of the surrounding natural desert" (Lougeay et al. 1996, p. 88). top
One can speculate that perhaps by converting the natural desert to residential use, there may be some actual cooling effect. But, when the other elements of urbanization are added—roads, parking lots, businesses, factories, and schools—the cumulative impact probably is warming. However, we simply do not know the extent of the impact. Changes are occurring that certainly have significant local and regional climate impacts and perhaps even global consequences but we simply do not know the extent.
The impacts of urbanization in the Sonoran desert are dramatic, especially on plants and animals, the natural drainage, visual quality and the regional climate. There are methods to understand these impacts and to take action to ameliorate their negative consequences. A first step is the development of a framework for studying environments affected by urbanization.
Understanding the Affected Environment top
Ian McHarg developed the "layer cake model" (Figure 3: Baseline natural resource data necessary for ecological planning) to understand the natural environment. He suggested that environmental data be collected sequentially and chronologically to understand causality. The idea is to explore interrelationships among processes that are revealed in landscape patterns. For example, older components of the environment, such as geologic features influence more recently formed elements like soils and vegetation. McHarg's layer cake forms the theoretical basis for most geographic information systems (GIS). Although GISs use the concept of layering, too frequently the importance of the sequences of the layers and causality is overlooked.
McHarg (1997) also provided a list of the baseline data necessary for collecting information about environments potentially affected by land-use change. McHarg's list includes the key data for climate, geology, hydrology, physiography, soils, vegetation, and wildlife as well as important human land-use information (Table 3). The specific information varies from place to place depending on the situation.
We have conducted several studies of the Desert View Tri-Villages area. Graduate environmental planning students at Arizona State University (ASU) conducted a thorough ecological inventory and an environmental impact assessment of the 110-square-mile area (Bagley et al. 1995; Ciekot et al. 1995). Several ASU environmental resources classes undertook detailed studies of the soils, vegetation, and wildlife in the area. Subsequently, one of our students compiled a detailed bibliography as an intern for the City of Phoenix (Coomer 1995). We are currently building a GIS database of the region and working with the City of Scottsdale on similar studies in areas to the east of the Desert View Tri-Villages.
Environmentally Sensitive Areas top
A collection of such baseline information can help identify environmental sensitive areas, which can be defined as "places vulnerable to negative environmental impacts, such as unstable soils, steep slopes, flood plains, wetlands, and certain plant and animal habitats" (Steiner, 1991, p. 321). States, such as Washington and local jurisdictions, like Scottsdale, require the protection of environmentally sensitive areas. The State of Washington protects environmentally sensitive areas through its state environmental policy act provisions. In Washington, city and county governments are encouraged to designate areas as environmentally sensitive. Such areas then are subject to more rigorous environmental review requirements for proposed developments or land-use changes. Meanwhile, Scottsdale defines and regulates "land slopes of 15% or more in the mountains, unstable slopes, special features, water courses, geologic conditions, and native slopes" as environmentally sensitive (City of Scottsdale 1991, p. 4).
In the Desert View Tri-Villages area, we identified steep slopes and washes as especially sensitive. These areas are potentially eligible for protection through the Arizona Preserve Initiative. If protected, they could provide an ecological spine for North Phoenix. My colleagues Joe Ewan and Rebecca Fish Ewan have worked with the City of Phoenix, Department of Parks, Recreation and Libraries to identify the boundaries of the washes for protection, using a combination of vegetative and landform characteristics for protection. They have completed a study of Cave Creek Wash (Ewan and Fish Ewan 1996) and are currently studying Apache Wash, Skunk Creek Wash, and two others. Their recommendations for the Cave Creek Wash have been adopted by city officials.
Land Suitability Analysis top
Land suitability analysis (LSA) methods are used for identifying the best places to locate future land uses. LSA methods rely on the comprehensive collection of natural resource information as summarize in Table 3. (See McHarg 1969 or Steiner 1991 for more detailed discussion.)
According to Klosterman (1997) suitability analysis involves three basic steps:
McHarg and his colleagues have suggested a seven-step process with similarities to Klosterman's three steps. The McHarg steps include:
(Steiner 1991) top
These steps can be applied for determining the best locations for future land use in the Sonoran desert. Let's use suburban housing as an example. What are the requirements for suburban housing? We would like a favorable microclimate, on rocks and slopes which are not too expensive to build on. A well-drained site would be nice and good soils for a garden. So we would relate these requirements to natural factors: north-south site orientations, flat sites with rocks that aren't too hard and soil types with good permeability. All these phenomena can be mapped and reveal opportunities for suburban land use. But, Sonoran sites also have constraints: washes that flood, caliche soils, endangered plants and animals, and spectacular views. These factors can be mapped too and overlayed with the opportunities to reveal suitable places for suburban housing. But suburban housing is but one potential land use. Areas which simply should be protected for preservation sake as well as places for recreation, industry, schools, gas stations, grocery stores, and roads can also be identified in a similar manner and then overlaid with the best places for housing. Many places will be suitable for several uses. As a result, it is crucial for policy-makers and citizens to determine which land uses should take precedent over others.
Conclusion top
The Sonoran desert is a unique, beautiful ecosystem. The region is experiencing one of the most rapid rates of urbanization in the United States. This late 20th century urbanization has consumed much space. An acre an hour is converted to urban land use in the Phoenix metropolitan region alone. As a result, it is crucial that the impacts of the urbanization be understood. Such understanding should lead to wiser decisions about the future of the region.
References top
Bagley, Anubhav, Ann Bennette, Jim Haklik, Harold Housley, Jim McCarthy, and Lizi Mcgeorge. 1995. Draft Environmental Impact Statement, Northwest Portion of Peripheral Areas C and D, Phoenix, Arizona. Tempe: School of Planning and Landscape Architecture, Arizona State University.
Balling, Robert C., Jr. and Sandra W. Brazel. 1986. "New Weather in Phoenix? Myths and Realities. Weatherwise (April):86-90.
Ciekot, Stephanie, Carol Hayden, Carlos Licon, Gary Mason, Jim McCarthy, and Jane Ploeser. 1995. Desert View Tri-Villages, Ecological Inventory and Analysis. Tempe: School of Planning and Landscape Architecture, Arizona State University.
City of Phoenix. 1987. General Plan: Peripheral Areas C and D. Phoenix, Arizona.
City of Phoenix. 1995. Infrastructure Financing Plan. Phoenix, Arizona.
City of Scottsdale. 1991. ESLO Users' Manual. Scottsdale, Arizona.
Coomer, Dawn. 1995. Peripheral Areas C and D Resource Guide. Phoenix: City of Phoenix Planning Department.
Ewan, Joseph and Rebecca Fish Ewan. 1996. Cave Creek Wash Preservation Boundary Study. Tempe and Phoenix: School of Planning and Landscape Architecture of Arizona State University-Main and Life Sciences Department of Arizona State University-West.
Forman, Richard T. T. 1995. Land Mosaics: The Ecology of Landscapes and Regions. New York: Cambridge University Press.
Klosterman, Richard E. 1997. "The What if? Planning Support System." www.dcigis.com/whatif/whatif.htm
Lougeay, Ray, Anthony Brazel, and Mark Hubble. 1996. "Monitoring Intra Urban Temperature Patterns and Associated Land Cover in Phoenix, Arizona Using Landsat Thermal Data." Geocarto International 11(4):79-89.
McHarg, Ian L. 1969. Design with Nature. Garden City, New York: Doubleday/Natural History Press.
McHarg, Ian L. 1997. "Natural Factors in Planning." Journal of Soil and Water Conservation 52(1):13-17.
Northeast Phoenix Partners. 1995. Desert Ridge: Master Planned Community. Desert Ridge sales brochure. Phoenix, Arizona.
Ortolano, Leonard. 1984. Environmental Planning and Decision Making. New York: John Wiley and Sons.
Ostler, Jolene. 1995. City of Phoenix planner. Interview.
Steiner, Frederick. 1991. The Living Landscape. New York: McGraw Hill.