Urban Systems
Post on 23-Feb-2016
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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”
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