Urban Climate

Question 1

What is the urban heat island effect?

Answer 1

Urban areas are warmer than rural areas. Urban areas with higher temperatures than the surrounding rural areas are called urban heat islands.

Question 2

Characteristics of an urban heat island

Answer 2

The highest temperatures are found in the densely built up areas eg the CBD

There are pockets of cool air above parks and bodies of water called temperature sinks

Same land use usually means same temperature but when land use changes temperature can rapidly change

Question 3

Four main causes of the UHI effect - absorption of heat by urban surfaces

Answer 3

Absorption of Heat by Urban Surfaces - absorb and store heat from the sun during the day and slowly release the heat as long wave radiation - most noticeable at night when it warms the air.

Question 4

Four main causes of the UHI effect - Air Pollution

Answer 4

Air pollution from cars and factories increases cloud cover over the city and creates a pollution dome that traps outgoing heat radiation and reflect it back to the surface.

Question 5

Four main causes of the UHI effect - heat from human activity

Answer 5

Cars, factories,offices,central heating, air conditioning and people themsleves all release heat

Question 6

Four main causes of the UHI effect - less evapotranspiration

Answer 6

when it rains water is quickly removed by drainage systems so little surface water to evaporate and less vegetation means less transpiration. Evapotranspiration uses heat energy so less means higher temperatures.

Question 7

UHI effect varies seasonally and diurnally (between night and day)

Answer 7

The UHI effect is stronger at night as rural areas cool down at night but urban surfaces continue to release heat that has been absorbed in the day.

Its stronger in the summer because there is more solar radiation so urban areas absorb more heat.

Its stronger when there is an anticyclone where there are clear skies and low winds as warm air isnt blown away

Question 8

Winds are affected by buildings in urban areas

Answer 8

Average wind speed is usually lower in cities than in rural areas because tall buildings create friction that slows moving air. There are areas where wind speed is zero because some areas are totally sheltered from wind by buildings. Canyon effect when powerful gusts of wind are channelled down streets

Question 9

Reasons for more rain fog and thunderstorms in urban areas.

Answer 9

The UHI effect means the air in urban areas are warmer and warm air can hold more water. Urban areas generate huge amounts of dust and pollution and these particles act as a condensation nuclei which encourages clouds to form and also increases the fog