urban systems
DESCRIPTION
Urban Systems. 1M inhabitant Cities w. Definitions Census; 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. Urban Sprawl. “Where” Loss of Ag Lands Natural Disasters. - PowerPoint PPT PresentationTRANSCRIPT
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Urban Systems
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1M inhabitantCitiesw
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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
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UrbanSprawl
“Where”
Loss of AgLands
NaturalDisasters
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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
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Is the Global
Urban Population Growth Rate
increasing or decreasing?
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Urban Growth RateIs
Decreasing
World ~ 1.5%/year
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50 % More than 50% of the world’s populationlives in cities
Only Asia and Africahave > 50% rural populations
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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”
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• Urban Heat Islands• Urban Hydrology• Urban Water Quality Issues
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Urban Heat
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Heat Waves; “Silent Killer”
Increases mortality associated with excessive and prolonged heatTypically associated with urban environments
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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”
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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
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Mean temp
2003 Temp
Dailymortality
ParisFrance
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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
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Urban temperatures can be 12ºF greater
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Diurnal variation in Air temperature
Greatest difference in late afternoon
Urban areas donot cool asquickly as
Rural
Greatest differenceNear mid-night
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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
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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
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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..
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Modeled Risk > 65, poor, living alone
Satellite DataCensus Date
~ 24% varianceIn mortality
Identify areas of risk
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Did it work?Philadelphia Heat Waves
93 vs 02• 1993 Heat wave
–115 deaths• 2002 Heat wave
–33 deaths
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• Urban Heat Islands• Urban Hydrology• Urban Water Quality Issues
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Precipitation100%
ET = Interception + transpiration
Throughfall
GroundwaterRunoff
Surface Runoff
To stream channel
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Precipitation100%
Interception ~ 0Transpiration = 0Evaporation ~ 0
Throughfall = PStemflow = 0
Groundwater runoff = 0
Surface Runoff ~ PMore waterdownstream
How does Urbanization influence water cycle?
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Issues & Options
• Issues: Urban runoff– Downstream flooding– Water quality; CSO
• Options– Precipitation Management; urban heat islands– ET Management; vegetation management– Runoff Management
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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
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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
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Land cover modifies travel time, water useUrban = faster travel time, lower water use = higher peaks, greater
volume
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Urban Flooding; “more water coming faster”
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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
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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
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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
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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
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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”