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Managing Environmental Problems and the Urban
Microclimate IB Geography II
Part 1
Close Reading Activity
• “Cities Make Own Weather Due to Trapped Heat” from the National Geographic.
• As you close read and annotate, – Use Context Clues to try and define “Urban Heat-Island
Effect” – Answer: How do cities impact temperature? Find
specific evidence that supports your answer. – Answer: What trends in temperature can we expect due
to increasing urbanization? – Answer: How can trees be the solution?
The Brown Agenda
• Environmental problems in urban areas vary over time as economic development progresses.
• The greatest concentration of environmental problems occurs in cities experiencing rapid growth (such as Mexico City)
• The Brown Agenda: the concentration of environmental problems. It has 2 main components: – Issues caused by limited availability of land, water
and services– Problems such as toxic hazardous waste,
pollution of water, air and soil, and industrial accidents.
Traffic Problems in LEDCs/MEDCs
• LEDCs– Private car ownership is
lower – Many cars are poorly
maintained and high polluters
– Heavy reliance on affordable public transport
– Journeys are shorter but take longer
– Less dependence on car, but growing.
• MEDCs– Increased number of motor
vehicles – Increased dependence on cars
as public transport declines – Major concentration of
economic activities in CBD– Inadequate amount of roads
and parking – Frequent roadwork – Urban sprawl results in long
trips to work.
Microclimate
The climate at a very local scale that influences the presence and distribution of organisms is known as the microclimate.
Structure Of Air Above Urban Area
• Greater amounts of dust particles in air.
• There is less water vapor because water is removed quickly by drainage and sewers.
• There is less vegetation to take in water and release it later, but more CO2 and higher proportions of toxic fumes due to fuels and discharge of waste gases by industry.
Structure Of The Urban Surface
• More heat retaining materials with lower albedo (reflectivity).
• Rougher surfaces, with a great variety of perpendicular slopes facing different aspects.
• Tall buildings can be very exposed, and the deep streets are sheltered and shaded.
Temperatures• Stronger heat energy retention and release, including
fuel combustion, gives significant temperature increases from suburbs into the centre of built-up areas creating heat “islands”.
• These can be up to 8 degrees warmer during winter nights.
• Snow in rural areas increases albedo, thereby increasing the differences between urban and rural.
Urban Heat Island Effect
• Urban areas are generally 2-4 degrees warmer than those in the surrounding areas.
• This creates an Urban Heat-Island (UHI) or the Urban Heat-Island Effect
• Its intensity is the temperature difference between the urban and the rural area.
• http://education.nationalgeographic.com/education/encyclopedia/urban-heat-island/?ar_a=1
Urban heat profile
Impact of Buildings
• Tall buildings will give cooler temperatures at street level, as not as much radiation from the sun is able to reach it.
• Short buildings will heat up the street level as it allows radiation to be reflected between buildings.
• Buildings will also reduce wind speeds (so its warmer) or will channel them (so it’s very windy)
Question to Think About
• Why does the urban heat island effect matter?
• Consider: – Increasing rates of urbanization – Increasing affluence – Possible links to global warming – Positive feedback mechanisms- hotter cities
create more heat.
Part 2
Socioeconomic Impacts of the UHI
• Human Health: high levels of ozone, suspended heat cause serious respiratory problems for the elderly, sick, and children.
• Human Discomfort: high levels of humidity, atmospheric dust, and poor air quality worsen the quality of life in cities for many
• Disease: higher temps increase the likelihood of vector and waterborne diseases in poor cities.
Socioeconomic Impacts of the UHI
• Energy Waste: high levels of energy used in air conditioning systems are an increasing concern
• Heat Stress and Illness: working days are lost and productivity lowered
• Environmental Degradation: Intense heat causes the degradation of urban fabric such as rubber and tarmac, creating long-term cost to city governments.
Factors Influencing Urban Heat Island Intensity
• Weather Conditions: clear and calm with no wind intensify UHI
• Topography/hydrology: inland cities far from water have higher UHIs
• City population size and density: large population consumes more energy and generates more air pollutants
• Level of economic development: developing cities have high density and high energy consumption, but weak emissions controls.
Factors Influencing Urban Heat Island Intensity
• Building and Street design: narrow streets are cooler by day, but retain heat at night
• Land Surface Cover: Concrete and asphalt have a high thermal capacity and absorb solar radiation during the day and release it as heat at night.
• Anthropogenic Heating: moving or stationary traffic and air conditioning units increase UHI intensity
• Air Pollution: causes heat retention and increases UHI intensity.
Why Do We Care About Heat Islands?
• Heat islands can affect communities by– increasing summertime peak energy demand– air conditioning costs– air pollution and greenhouse gas emissions– heat-related illness and mortality– water quality.
High Energy Demand
• Increased energy consumption: – Higher temperatures in summer increase energy
demand for cooling and add pressure to the electricity grid during peak periods of demand.
– One study estimates that the heat island effect is responsible for 5–10% of peak electricity demand for cooling buildings in cities.
Increased Emissions
• Elevated emissions of air pollutants and greenhouse gases: – Increasing energy demand generally results in
greater emissions of air pollutants and greenhouse gas emissions from power plants.
– Higher air temperatures also promote the formation of ground-level ozone.
Quality of Life
• Compromised human health and comfort: – Warmer days and nights, along with higher air
pollution levels, can contribute to general discomfort, respiratory difficulties, heat cramps and exhaustion, non-fatal heat stroke, and heat-related mortality.
Water Quality
• Impaired water quality:– Hot pavement and rooftop surfaces transfer
their excess heat to stormwater, which then drains into storm sewers and raises water temperatures as it is released into streams, rivers, ponds, and lakes.
– Rapid temperature changes can be stressful to aquatic ecosystems.
What Can Be Done?
What Can Be Done?
1. Green Roofs • A green roof is a roof of a building that is partially or
completely covered with vegetation and soil• The term "green roof" may also be used to indicate roofs that
utilize some form of "green" technology, such as solar panels 2. Cool Pavement
• The term refers to materials chosen to reduce pavement temperature by increasing pavement reflectivity or controlling temperature by other means through choice of materials and engineering design
3. Construction of Previous Pavement• Pervious pavements can be made of concrete or asphalt,
open-celled stones, and gravel, that are mixed in a manner that creates an open cell structure allowing water and air to pass through.
Advantages• Because pervious pavements allow rainwater
to seep into the ground through the pavement:– Vegetation is watered, reducing
the need for irrigation – Ground water is recharged – Water resources are preserved – Stormwater runoff is reduced – Stormwater runoff quality is
improved
Question to Think about: Identify and describe TWO differences between urban and
surrounding rural areas that contribute to the temperature differences between them.
Part 3
• Urban Heatwaves
Urban Heat waves • A heat wave is a prolonged period of
excessively hot weather, which may be accompanied by high humidity
• A growing problem due to global warming.
• They catch urban societies unprepared and unaware and can result in high mortality rates.
• Increasing risk with urbanization and the rapid growth of megacities.
Heat Waves
• In the United States, heat waves kill more people than all of the so-called “natural disasters” combined.
• In Chicago, more than 700 people died during one week of 1995.
• http://www.youtube.com/watch?v=lCWJsgeFUe4
(4:18)
Paris Heat wave of 2003
• http://www.youtube.com/watch?v=Hx2940wcooo (3:51)
Paris Heat wave of 2003
• Close Reading Activity• Questions for Think-Pair-Share
– Referring to Figure 11.30 and 11.31, describe the patterns for day and night-time temperatures (describe general pattern over whole area for both maps and name and locate areas that have temperature anomalies)
– Suggest reasons for the patterns you have found. (Hint- use evidence from Keys to help)
