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World indicators on the environmentWorld Energy Statistics - Time SeriesEconomic inequality
World Resources 1996-97
(A joint publication by The World Resource Institute, The United
 Nations Environment Programme, The United Nations Development
 Programme, and the World Bank)
(Data edited by Dr. Róbinson Rojas)

3. Urban Impacts on Natural Resources


Sometime around the year 2025, 8 billion people will be living on the planet (1). These people will require land, energy, water, and food, regardless of whether they live in cities or in rural villages. As their incomes rise, they will consume greater quantities and varieties of goods and, in the process, will generate greater quantities of wastes.

How this population growth and economic expansion will affect the environment has been a matter of debate for some time, but now there is a new dimension. By 2025, the majority of the world's population, some 5 billion people, will be living in urban areas (2)--a transformation that is bound to change the nature and scale of humanity's impact on the environment.

Cities are inextricably linked with the economic shift from an agrarian society to one based on manufacturing and services. Thus, disentangling the impacts of urban growth from those of economic growth and industrialization is difficult and perhaps impossible.

Still, urban settlements, with their dense agglomerations of people and economic activities, put different pressures on the environment than do rural settlements. These differences are more pronounced in the developing world because rural settlements there are still primarily traditional villages, where buildings are made of local materials and residents are still largely dependent on their own resources for their livelihood (3). The distinction is less clear in the developed world, where rural and urban residents alike tend to benefit from the same modern goods and services, such as piped water, paved roads, electricity, and telecommunications (4).

Urban areas affect the environment through three major routes: the conversion of land to urban uses, the extraction and depletion of natural resources, and the disposal of urban wastes. As cities expand, prime agricultural land and habitats such as wetlands and forests are transformed into land for housing, roads, and industry. The nexus of people and economic activity (including manufacturing, services, and commerce) in cities requires resources far in excess of what the local area can supply, so cities must draw their essential supplies of food, fuel, and water from distant places. The concentration of wastes in cities is much higher than that in the countryside, reflecting both the sheer number of people living in a relatively small area and their greater levels of consumption. As a result, urban wastes may quickly overtax the ability of local ecosystems to assimilate them.

The scale of urban consumption and waste generation--and the negative impacts associated with them--varies dramatically from city to city, depending in large part on a city's wealth and size. Not surprisingly, the highest levels of resource use and waste generation tend to occur in the wealthiest cities and among the wealthier groups within cities (5) (6). Thus, wealthy cities contribute disproportionately to global environmental problems, such as depletion of natural resources and emissions of greenhouse gases.

By contrast, per capita resource use and levels of waste generation tend to be quite low among the urban poor. Predominately poor cities thus tend to pose minimal threats to the global environment, but their local impacts can be severe. The urban poor, lacking an alternative place to live, often establish informal settlements in ecologically fragile areas. When these settlements are unserved by sewers or garbage collection services, wastes accumulate and degrade land and local watersheds.

Yet cities of all types also offer important opportunities for protecting the environment. With proper planning, dense settlement patterns can reduce pressures on land from population growth and can also provide opportunities to increase energy efficiency. Recycling becomes more feasible because of the large quantities of materials and the number of large and small industries that can benefit from it (7). And although high densities may exacerbate pollution problems, developing the infrastructure required to manage wastes may be easier and more cost-effective in an urban setting (8) (9).

Urbanization may help improve the environment in indirect ways as well. Birth rates are three to four times lower in urban areas than in rural areas, thereby reducing environmental pressures from population growth (10). Cities provide opportunities to educate residents about environmental issues and mobilize residents around these issues. In addition, per capita expenditures on environmental protection are higher in urban areas, both in absolute terms and as a percentage of the gross national product (11). Many cities are also taking an active role in environmental management, from developing local strategies to protect regional biodiversity and natural resources to joining forces in an effort to reduce global greenhouse gas emissions (12) (13).

To the extent possible, this chapter concentrates on environmental issues that arise directly from urbanization and urban activities rather than the broader set of environmental pressures linked to economic growth and industrialization. In many cases, however, a city's environmental impacts are as much a product of development as they are of urbanization, and the two cannot be teased apart. Although industrial pollution is generated as a result of activities performed to satisfy broad consumer demand--not just urban demand--the impacts are often concentrated around or downwind of cities. Cities per se are not responsible for the rise in greenhouse gas emissions, but the higher consumption patterns linked with urban lifestyles may be--and urban policies could do much to reduce those emissions.

Another difficulty in gauging the full impact of urban areas on the natural environment lies in the still-rudimentary understanding of complex ecological processes. Although abundant research has linked pollution pressures to damage to aquatic or terrestrial life, the total impacts on ecosystems are difficult to measure, so studies are often more descriptive than quantitative. When evaluating the impacts of urban activities on human health, for instance, the endpoints can be measured in terms of illness and death rates. Few equivalent measures exist for assessing the health of ecosystems.

Few attempts have been made to look at the overall impacts of cities on the environment, as opposed to the more specific impacts of a particular sector such as transportation (14). In the past few years, a number of researchers have begun looking at the issue of cities and sustainable development--in other words, how cities can meet development needs with lower draws per capita on environmental capital (15) (16) (17). In a similar vein, recent attempts have been made to calculate a city's "ecological footprint"--the amount of productive land needed to sustain a city's population and its consumption levels (18) (19). Further research in this area is warranted because the shift toward a predominately urban world appears inevitable. Understanding the environmental impacts of urban areas may provide useful insights into how urban growth can be channeled in positive ways to help reduce humanity's pressures on the global environment.

This chapter provides an overview of how urban areas and related activities affect the environment through land conversion, the extraction and depletion of natural resources, and the disposal of urban wastes. The chapter then takes an in-depth look at the combined impacts of urban areas through two case studies of coastal ecosystems. Although only one of many ecosystem types, coastal ecosystems are especially threatened by urban development and land- based pollution. Already, 40 percent of all cities with a population of 500,000 or greater are located on tidal estuaries or the open coastline. The damage to these ecosystems is worrisome because coastal ecosystems are some of the most productive on the planet. Although the ecosystems of the coastal zone occupy just 8 percent of the global surface, they are responsible for some 26 percent of all biological production, according to one estimate (20).

These case studies vividly illustrate the extent of damage caused by multiple impacts and the need for integrated approaches to addressing urban environmental problems. Further policies for mitigating adverse effects on natural resources and maximizing urban advantages are explored in Chapter 5, "Urban Priorities for Action."

Topics Covered in Chapter 3Land Conversion
•Extraction and Depletion of Natural Resources
•Urban Wastes
•Integrated Approaches to Protect the Resource Base


•Water: The Challenge for Mexico City
•Los Angeles Copes with Air Pollution

References and Notes

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