3.4 Urban Climate Flashcards
Climatically, how are urban areas and their surrounding countryside different?
Temperature- higher Humidity- lower Precipitation- more Visibility- worse (more fog) Air quality- worse (more dust particles) Wind speed- lower
What is the effect of a UHI?
Higher temperature (1-3*C) Dependant in season, weather conditions, sun intensity and ground cover
Why do urban areas tend to be slightly warmer than their surrounding areas?
The building materials absorb more heat and are less reflective
Pollution from industry and cars increases cloud cover and that absorbs outgoing radiation
Water falling to the surface is disposed of quickly so more energy is used to heat the atmosphere than would have been used for evapotranspiration
Large concentration of people, industry, homes and vehicles which all release heat
Why does the UHI effect matter?
Human health- respiratory problems, heat stroke, high pollen levels
Disease- high temperatures increase spread of vector and waterborne disease in poor cities
Air conditioning uses high amounts of energy
Increased risk of material deterioration- historical monuments etc
What factors could increase the intensity of the UHI effect?
Urbanisation- higher percentage of people/traffic/industrial activity
Economic development- more buildings
Anthropogenic heating- from vehicles, heating and air con
Air pollution- increases particulate matter in the atmosphere which retains more heat
Why are precipitation levels different in an urban area than rural?
Temperatures are higher which heats the ground so rapid evaporation takes place
Industrial sources and power stations produce water vapour
Pollutions provides nuclei to assist raindrop formation
Presence of high-rise buildings at a mixture of heights generates air turbulence and rises
All of these abuse cumulus cloud to build from which heavy rain falls
How does fog form?
Particles in the atmosphere act as condensation nuclei for fog formation
Common in cities undergoing industrialisation with no legalisation (eg Clean Air Acts) eg Beijing, New Delhi
How do thunderstorms form?
Cumulonimbus clouds form, though which uplifted air cools rapidly and condensation
Latent heat is released during cooling which fuels further uplift
Positive electrical charges build up in cloud and when it is high enough to overcome resistance, lightening is produced
Thunder is a shock wave produces when extreme temperatures cause rapid expansion of air
What effects do urban structures have on wind?
Varying heights and uneven surfaces of buildings produce frictional drag
High rise buildings channel air through the gaps between them
Upward convectional processes can draw in air from cooler surroundings
When air flows between buildings the air movement is effected by the Venturi effect, where the pressure within the gap caused the wind to pick up speed
What makes air quality in urban areas poor?
Particulate pollution
Temperature inversions where cool sinking air can become trapped below a layer of warm air
Photochemical smog (low level oxygen pollution associated with cars and pollution; often occurs when there is a weather system of descending stable air eg anticyclone)
Explain the impact of nitrogen dioxide?
It reacts with hydrocarbons in sunlight to create ozone which contribute to the formation of particles
Road transportation accounts for 50% of emissions
Can inflame the lining of the lung
Accelerate the weathering of buildings (acid rain)
Outline some strategies to reduce pollution and the UHI effect?
Lighter coloured cars to reflect heat
Roofs built from materials that reflect sunlight
Opening up spaces to create ventilation and lower temperatures
Green roofs reduce temperatures/runoff, act as insulators and increase biodiversity
