Strand 5 Notes: Urban Climate Flashcards
(14 cards)
Why are urban areas warmer than rural areas?
An urban area or metropolitan area is significantly warmer than its surrounding rural areas because if human activity. The Venturi effect is wind funnelled into narrow urban canyons created by tall buildings, speeding up as it becomes more restricted.
What are the issues? eg.London’s pea Souper
Acid burns back of throat, bringing choking fits so risk of health problems. Increases mortality. Increase air pollution. Visibility reduced to a couple of yards. Drivers can’t see as far as own car headlights. Fog was murderous, people & animals suffocated in appalling numbers. Increases energy cost (for air conditioning), more than 100, 000 suffered breathing problems. General discomfort. More fires if extreme temperatures. Heat strokes/cramp.
Strategy for managing the UHI
Sky view factor: amount of sky we can see without our view impended by tall buildings.
Green roofs: planting vegetation on roofs can capture airborne pollutants, and filter noxious gases for cooling the surrounding atmosphere.
Cool cars: swapping conventional cars for electric ones, reduce fossil fuels which are heating/ polluting environment. Smaller air conditioner in cars.
Cool surfaces: installing cool- mainly reflective roofs like solar panels or glass windows which absorb sun’s heat & reflect it.
Urban greening: tree planting around a building or using reflective surface roofs has a direct influence on the structure’s energy balance/cooling needs.
Micro climate
A local set of atmospheric conditions that differ from those in the surrounding areas, often slightly but sometimes sustainably. A smaller area that differs from the surrounding macro climate.
Albedo
Measures of how much light hits a surface is reflected without being absorbed. Lower Albedo if reflected more.
Urban heat island
Urban area/ metropolitan significantly warmer than surrounding areas.
Precipitation - why is it heavier & more frequent?
Pollutants in the air in urban environments create more cloud cover & precipitation, giving higher temperatures & reduced sunlight. 10% more cloud cover than rural areas.
Other climate issues :
Thunderstorms - higher temperatures mean higher likelihood of thunderstorms increased by 25% they development not humid air & are accompanied by violent rain, thunder & lighting
Winds - created as air moves from areas of high pressure to areas of low pressure. Any obstacle alters wind flow. Urban areas have lower wind speeds than rural due to friction with buildings & the windbreak effect.
Specific heat capacity
Measure if energy required to raise temperature of 1kg of material by 1degrees.
Anthropogenic heat
Heat given off by human activity (eg. Vehicles/ central heating). Adds to urban environment & raise its temp. The UHI also cause convention & can increase precipitation.
Impacts of UHI
1) The sun heats the ground surface - evaporation
2) Radiated heat from ground surface, warms air above it.
3) The warm air rises
4) As it rises, it cools & condenses, leading to cloud formation, fog, rain, & thunderstorm formation.
The UHI effect
Urban environment also influences local meteorology. The UHI effect increases convention, leading to showers & increasing the chance of possible thunderstorm development by up to 25% compared to surrounding rural areas. Low pressure caused by this uplift draws moist air into the city from the surrounding countryside, leading to increasing incidence of fog & cloud formation & risk of rain. Urban areas can receive up to 10% more frequent cloud cover than surrounding rural areas.
Wid is created as air moves from areas of high pressure to areas of low pressure. Any obstacle to this movement alters wind flow. Urban areas have lower wind speeds than rural areas due to friction with buildings & the windbreak effect.
Particulate
The release of particles & noxious gases into the atmosphere (often fossil fuel combustion)
Photochemical
Creates smogs consisting if ozone & peroxyacetylene nitrate (PAN)
Urban transport solutions
Road schemes such as urban bypasses. Park & ride, congestion charge introduced in London in 2003. Mass transit systems, such as the ‘metro-link’ in Manchester.
