Urban Ecosystems

How does a city get started?• Usually an historic trade route or location near

some valuable resource, e.g. water• Usually without any long-term planning• Usually in an area where it

is easiest to build structures,

e.g. flat or gentle terrain

(interesting exceptions

– San Francisco!)

How is a city structured?

How is a city structured?

• Most are structured through historical “accidents”

• Most do not have large, open “green spaces”

• Zoning has segregated living areas from business areas to some extent

What problems have developed because of these structures?

Problems with water• Runoff is usually polluted. With what?

• Urban runoff – fast, furious with little percolation. Why?

• Urban flooding results from this.

Some possible solutions from the Los Angles Demonstration

House

Cisterns for collecting rainwater

Vegetated Swales for moving water and retaining it within

specified areas

In this case, they used mulch rather than vegetation

Retention Structures

Driveway Collection ‘Well’

What problems have developed because of these structures?

Problems with air• Air quality is bad in cities due to

– Automotive sources– Industrial sources– Smoke from other sources

• Air quality is also bad due to lack of absorbing surfaces

What problems have developed because of these structures?

Urban Heat Island Effects

Suburban day Suburban day Suburban night

Urban day Urban day Urban night

Atlanta, GA

1973 1976 1983

1987 1992 1997

Atlanta, GA

1971

1997