urban climate Flashcards
what are the four main causes of the urban heat island effect?
Absorption of heat by urban surfaces - concrete, brick and tarmac store heat from sun during day. slowly release heat as long wave radiation over night.
Air pollution - from cars and factories, increase cloud cover over city, create pollution dome, trap outgoing heat.
Heat from human activity - cars, factories, central heating and people etc all release heat.
Less evapotranspiration - when it rains water is quickly removed by drainage systems, so little water to evaporate and little vegetation so less transpiration.
precipitation in city?
greater, due to UHI generating convectional rainfall. also, pollution in city can create cloud coverages and there is more water vapour from industrial sources.
thunderstorms in city?
develop in hot humid air. extreme temps cause rapid expansion of air creating a shockwave heard as thunder. lightning occurs due to a charge building up and discharging over an area of negative charge in the cloud or on the earth.
fog in city?
more particles in city air, particles act as condensation nuclei and encourage fog formation at night. cities with industrialisation experience more fog formation e.g. airpocalypse, trapping pollutants creating toxic smog
wind in city?
urban structure will affect wind speed and frequency.
varying heights of buildings - powerful frictional drag, create turbulence.
High rise buildings - slow air movement, channel air into canyons.
when UHI is strong e.g on clear night, strong localised winds drawn from cooler surroundings.
Air Quality in city?
emission created by combustion of fuel.
CO, NO2, SO2 - contribute to bad air quality
will vary at different times of year, can be up to 6x greater in winter. smog was very common in 19th century due to coal burning e.g in London.
