Urban Systems

1M inhabitantCitiesw

DefinitionsCensus; people/area

• United States:– 386 /km2 (1000 people/mi2)– Surrounding area has 193/km2

• Japan– 4000 people/km2

• Australia– 200 people/km2 total and > 1000

UrbanSprawl

“Where”

Loss of AgLands

NaturalDisasters

Coastal Population Bomb Areas < 5 miles of coast are growing 3x the national average

Development in high-risk coastal areas increased 60% between 1980-2000

Is the Global

Urban Population Growth Rate

increasing or decreasing?

Urban Growth RateIs

Decreasing

World ~ 1.5%/year

50 % More than 50% of the world’s populationlives in cities

Only Asia and Africahave > 50% rural populations

Environmental Advantages/Disadvantagesof Urban Areas

• Advantages of higher population density– Lower per capita transportation energy use– Higher access to education, health care..– Lower ecological foot-print

• Disadvantages of higher population density– Public Health; crime, disease – Concentration of pollution– Loss of connection to nature

• “Humanity overtakes Nature with Fossil Fuels”

• Urban Heat Islands• Urban Hydrology• Urban Water Quality Issues

Urban Heat

Heat Waves; “Silent Killer”

Increases mortality associated with excessive and prolonged heatTypically associated with urban environments

Public Perception of Heat Waves“silent killer”

• Impact people who live alone– Poor, elderly, sick, alone have highest risk– Increasing % of population live alone

• Minor Property Damage• Slow and preventable• “Forgotten as soon as temperatures drop”

2003 European Heat WaveHottest since 1500 AD

Up to14,800 deaths in France35,000 deaths in Europe

Melting of MatterhornTriggered rock slides

High ozone levelsEarly & poor wine season

10 C hotter New Scientist, Oct 03

Daytime Temp difference 7/03-7/02

Mean temp

2003 Temp

Dailymortality

ParisFrance

Why are urban areas hotter?

1. Heat produces by urban activities– Air conditioners, cars, factories, people…

2. Greater heat storage by structures• Buildings & pavement vs plants & water

3. Greater air pollution haze & cloud cover– Heat trap– Respiratory problems

4. Lower winds (urban canyons) – Less heat exchange

5. Lower Humidity: drier– More evaporation from human bodies

Urban temperatures can be 12ºF greater

Diurnal variation in Air temperature

Greatest difference in late afternoon

Urban areas donot cool asquickly as

Rural

Greatest differenceNear mid-night

Management Options?1. Heat produces by urban activities

– Increase efficiency, heat pumps to ground2. Greater heat storage by structures

– Increase vegetation; green roofs, tree lined streets, parks

3. Greater air pollution haze & cloud cover– Reduce discharge during peak periods

4. Lower winds (urban canyons) – Design of new buildings

5. Lower Humidity: drier– Maintain body fluids

Benefits Reduced energy loss Reduce urban heat Reduce storm runoff Sound insulation

Costs More expensive More Maintenance Not for all buildings

How to spendLimited fundsTrees vs Roofs

Philadelphia Heat Wave Prevention Plan• 1993 Heat wave; 115 deaths in over summer

• Warning system; (Stage 1, Stage 2)– Buddy system with block captains

• Media and education campaign • Utility subsidize; no terminations • Extended hours of senior service centers• Program for roof replacements, reforestation..

Modeled Risk > 65, poor, living alone

Satellite DataCensus Date

~ 24% varianceIn mortality

Identify areas of risk

Did it work?Philadelphia Heat Waves

93 vs 02• 1993 Heat wave

–115 deaths• 2002 Heat wave

–33 deaths

• Urban Heat Islands• Urban Hydrology• Urban Water Quality Issues

Precipitation100%

ET = Interception + transpiration

Throughfall

GroundwaterRunoff

Surface Runoff

To stream channel

Precipitation100%

Interception ~ 0Transpiration = 0Evaporation ~ 0

Throughfall = PStemflow = 0

Groundwater runoff = 0

Surface Runoff ~ PMore waterdownstream

How does Urbanization influence water cycle?

Issues & Options

• Issues: Urban runoff– Downstream flooding– Water quality; CSO

• Options– Precipitation Management; urban heat islands– ET Management; vegetation management– Runoff Management

ET Management • Direct: Manage land cover

– “cut down trees for more water” – Conifers vs evergreen vs deciduous – Agricultural use

• Indirect: – Wind breaks– Urban heat islands

Precipitation100%

Groundwater Shallow Deep

Surface Runoff

ET; manage land cover

Soil Moisture

Runoff Management“slow down water to use it later”

“get it out of here..”

Runoff ManagementManage Vegetation & Surface Manage infiltrationManage stream channels

1) Promote aquifer recharge 2) Storm water runoff ponds

3) Dams & reservoirs

Land cover modifies travel time, water useUrban = faster travel time, lower water use = higher peaks, greater

volume

Urban Flooding; “more water coming faster”

Water Quality Issues

• WQ for instream and off-stream uses– Drinkable vs swimmable vs industrial vs agricultural vs thermal

• Clean Water Act (1972)– “fishable and swimmable”– Water body assessments

“Water quality is a relative concept that reflects measurablephysical, chemical, and biological characteristics in relation

to a specific use”

Major pollutants and sources

Urban WQ Pollutants• Temperature; urban discharges & runoff

– 10C increase will double metabolic rate, 5C change can alter community structure

– Warm water from thermal plants– Warm water from street runoff– Cold water releases from dams

• Management; • Cool before it enters (cooling towers)• Warm before it enters (ponds)• Withdraw at different reservoir levels• Maintain riparian canopy cover

Urban WQ Pollutants• Nitrogen

– DNA, RNA, TNT, fertilizer & sewage, – Green house gas, smog, acid rain…– Most common water pollutant in USA;

• 2x pre industrial inputs– Increases algae, decreases DO…

• Management– Sewage Treatment Plants– Keep it out;

– fertilizer management– Runoff control; buffer zones

– Wetlands absorption

WQ Pollutants• Sediment

– Water clarity • temp, food production in aquatic environments..

– Modify habitat; • Fish spanning• Recreation

– Reservoir and channel filling; • loss of habitat, hydropower, increased flooding??• Navigation

• Management: • keep it out; upland controls, riparian buffers• Detention ponds trapping• Dredging

Vision for the Urban future

• Urban Clusters & high density housing– In geologically safe areas

• Integrated transportation & information – Less and more efficient transportation

• Urban gardens and green areas– Local food sources

• Incentives for reduced consumption

“learning how to live with less energy and a smaller economy”“doesn’t mean going backwards”