Chapter 27: Urban Environments

Transcription

1 Chapter 27: Urban Environments

2 City Life In the past, the emphasis of environmental action has most often been natural landscapes outside cities. Now it is time to turn more of our attention to city environments. Cities were thought of as polluted, dirty, lacking in wildlife and native plants, and artificial. Majority of people live in cities and have suffered directly from their decline.

3 City Life The NSF has added two urban areas, Baltimore and Phoenix, to its Long-Term Ecological Research Program Program that supports long-term monitoring of, as well as research on, specific ecosystems and regions.

4 City Life Today approximately 45% of the world s population live in cities. Economic development leads to urbanization; 75% of people in developed countries live in cities But only 38% of people in the poorest developing countries are city dwellers

5 City Life Megacities Huge metropolitan areas with more than 8 million residents In 1950, the world had only two: New York City and nearby urban New Jersey (12.2 million residents altogether) and greater London (12.4 million). By 1975, Mexico City, Los Angeles, Tokyo, Shanghai, and São Paulo, Brazil, had joined this list. By 2002, 30 urban areas on the list.

6 The City as a System Must maintain a flow of energy, provide necessary material resources, and have ways of removing wastes. City ecosystem maintained by transportation and communication with outlying areas. Not a self-contained ecosystem Takes in raw materials: food, water, wood, energy, mineral ores. Produces and exports material goods and ideas, innovations, inventions, and art. Cannot exist without a countryside to support it

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8 The City as a System The average city resident produces large amounts of waste each year. If exported w/o care, they pollute the countryside, reducing its ability to provide necessary resources for the city. With such dependencies and interactions between city and surroundings, relationships between people in cities and countryside have often been strained.

9 The City as a System Ways must be found to Make urban life healthy and pleasant Keep the cities from polluting the very environment that their dense human population in theory frees for other uses. City planning has a long history Defense and beauty Connecting cities in environmentally and aesthetically pleasing ways with surrounding mountains or water.

10 Site and Situation: The Location of Cities Cities are not located at random but develop mainly because of local conditions and regional benefits. They grow up at crucial transportation locations (situation). Can be readily defended, with good building locations, water supplies, and access to resources (site). Primary exceptions are for political reasons.

11 Site and Situation: The Location of Cities A good site includes A substrate suitable for buildings Nearby supplies of drinkable water Nearby lands suitable for agriculture and forest Easier to build a city where climate benign An excellent and important situation can compensate for a poor site I.e. New Orleans

12 New Orleans - Poor site, important situation

13 New York City - Good site and situation

14 Site and Situation: The Location of Cities Environmental situation strongly affects the development and importance of a city. Before railroads, automobiles, and airplanes, cities depended on water for transportation. Most early cities were located on or near waterways. major ocean harbors or at the fall line on major rivers

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16 Site Modification Site is provided by the environment, but technology and environmental change can alter a site for better or worse. Changes in a site over time can have adverse effects on a city. E.g. Bruges, Belgium

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18 City Planning and the Environment A danger in city planning is the tendency to transform a city center from natural to artificial features. To replace grass and soil with pavement, gravel, houses, and commercial buildings.

19 City Planning for Defense and Beauty City planning Formal, conscious planning for new cities. Two dominant themes have been defense (fortress cities) and beauty (park cities).

20 The City Park Parks have become more and more important in cities. A significant advance for US cities was the 19 th century planning and construction of Central Park in New York City, The first large public park in the US. Designed by Olmsted Example of design w/ nature

21 The City Park Olmstead also worked on projects in Boston The result of his vision was a control of water that was also an aesthetic addition to the city. Blending of goals made the development a landmark in city planning.

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23 The City Park An extension of the park idea was the garden city. City and countryside should be planned together. Surrounded by a greenbelt. The idea was to locate garden cities in a set connected by greenbelts, forming a system of countryside and urban landscapes.

24 The City as an Environment A city changes the landscape, and because it does, it also changes the relationship between biological and physical aspects of the environment. Many of these changes were discussed in earlier chapters as aspects of pollution, water management, or climate.

25 The Energy Budget of a City The city exchanges energy with its environment in the following ways: (1) absorption and reflection of solar energy (2) evaporation of water (3) conduction of air (4) winds (air convection) (5) transport of fuels into the city and burning of fuels by people within the city (6) convection of water (subsurface and surface stream flow)

26 The Urban Atmosphere and Climate Cities affect the local climate; as the city changes, so does its climate. Generally less windy than nonurban areas because buildings obstruct the flow of air. But buildings also channel the wind Receives less sunlight than the countryside Because of the particulates in the atmosphere over cities.

27 The Urban Atmosphere and Climate In spite of the reduced sunlight, cities are warmer than surrounding areas. Form heat islands for two reasons: Increased heat from the burning of fossil fuels and other industrial and residential activities. Lower rate of heat loss, partly because buildings and paving materials act as solar collectors

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29 Solar Energy in Cities Passive solar energy Used in Greece, Rome and China to heat household. Overlooked in America and Europe because of cheap fossil fuels. Importance beginning to be appreciated again. Photovoltaic devices now seen in many cities.

30 Water in the Urban Environment Paved city cause most rain to run off into storm sewers. Water in the soil also prevented from evaporating to the atmosphere. A process that cools natural ecosystems; Adds to heat island effect. Chances of flooding increase both within the city and downstream.

31 New, ecological methods of managing storm water can alleviate problems.

32 Water in the Urban Environment Most cities have a single underground sewage system. During heavy rain can cause the plant to carry sewage downstream

33 Soils in the City A modern city has a great impact on soils. Soils are no longer replenished by vegetation City soils, are more likely to be compacted, waterlogged, impervious to water flow, and lacking in organic matter.

34 Pollution in the City In a city, everything is concentrated, including pollutants. City dwellers are exposed to more toxic chemicals, human-produced noise, heat, and particulates Lives are shortened by an average of one to two years in the most polluted cities in the US.

35 Pollution in the City Sources of urban pollution Motor vehicles, stationary power sources, home heating and industry. The primary sources of particulate air pollution are older, coal-burning power plants, industrial boilers gas- and diesel-powered vehicles.

36 Bringing Nature to the City A practical problem for planners and managers of cities is how to bring nature to the city. Evolved into several specialized professions, including: Urban forestry landscape architecture city planning civil engineering specializing in urban development.

37 Vegetation in Cities Trees are increasingly used to soften the effects of climate near houses. Rows of conifers planted to the north of a house can protect it from winter winds. Deciduous trees to the south can provide shade in the summer, yet allowing sunlight to warm the house in the winter.

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39 Wildlife in Cities We can divide city wildlife into the following categories: (1) those species that cannot persist in an urban environment and disappear (2) those that tolerate an urban environment but do better elsewhere (3) those that have adapted to urban environments, are abundant there, and are either neutral or beneficial to human beings (4) those that are so successful they become pests

40 Urban Wilds City environments can contribute to conservation of wildlife in a number of ways. Urban kitchen gardens can be designed to provide habitats for endangered hummingbirds. Rivers and their riparian zones, ocean shorelines, and wooded parks can provide habitat for endangered species and ecosystems. Urban drainage structures can be designed as wildlife habitat.

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42 Animal Pests Most common city pests are cockroaches, fleas, termites, rats, and pigeons. Pests compete with people for food and spread diseases.

43 Animal Pests An animal is a pest to people when it is in an undesired place at an undesirable time doing an unwanted thing. Animals that survive best in cities have certain characteristics in common. Generalists in their food choice High reproductive rate Short average lifetime

44 Controlling Pests We can best control pests by recognizing how they fit their natural ecosystem and identifying their natural controlling factors. Often assumed that the only way to control animal pests is with poisons. Early poisons generally toxic to people and pets Another problem is that reliance on one toxic compound can cause a species to develop resistance, which can lead to rebound. One of the keys to controlling pests is to eliminate their habitats.