CUE 5 - Urban climate

Question 1

What is the urban heat island effect

Answer 1

The phenomenon or urban areas being warmer than rural areas

Question 2

What are urban heat islands (UHI)

Answer 2

Urban areas with higher air temperature than the surrounding rural areas

Question 3

Where are the highest temperatures found

Answer 3

In industrial areas and in the most densely built-up areas (CBD)

Question 4

What are temperature sinks

Answer 4

Pockets of cool air above parks and bodies of water (like rivers and ponds)

Question 5

What are plateaus?

Answer 5

Areas within the city with the same land use (like industry) generally have the same temperature

Question 6

What are rapid changes in temperature reffered as?

Answer 6

Cliffs

Question 7

When does temperature change rapidly

Answer 7

When land use changes (eg - from inner-city housing to CBD high rise buildings)

Question 8

What are the 4 main causes of the UHI effect

Answer 8

• Absorption of heat by urban surfaces
• Air pollution
• Heat from human activity
• Less evaportranspiration

Question 9

What surfaces absorb and store heat during the day

Answer 9

Concrete, brick and tarmac

Question 10

What happens to these surfaces

Answer 10

Slowly release heat as long wave radiation - its more noticeable at night when it warms the air

Question 11

What does air pollution from cars and factories do

Answer 11

Increases cloud cover over the city

Question 12

WHat does this create

Answer 12

A pollution dome (layer of pollution over the city

Question 13

What do these things do?

Answer 13

Trap outgoing heat radiation and reflect it back to the surface

Question 14

Where does heat from human activity come from?

Answer 14

Cars, factories, offices, central heating. Air conditioning units and people themselves

Question 15

What happens when it rains?

Answer 15

The water is quickly removed by drainage systems so there’s little surface water to evaporate

Question 16

What happens because theres not much vegetation

Answer 16

Theres little transpiration

Question 17

When is the UHI effect stronger

Answer 17

At night

Question 17

What happens if theres higher temperatures

Answer 17

Evapotranspiration uses heat energy, so higher, so higher temp means less evapotranspiration

Question 18

What are urban night temperatures like in comparison to rural areas

Answer 18

3 - 4 higher

Question 18

Why does this happen

Answer 18

Rural areas cool at night, but urban areas don’t cool as much because they continue to release heat that they’ve absorbed during the day

Question 18

Why is it stronger

Answer 18

There’ more solar radiation in summer so urban areas absorb more heat

Question 18

What are urban daytime temperatures like in comparison to surrounding rural areas

Answer 18

Theyre on average 0.6 higher

Question 18

What do anticyclones cause

Answer 18

Clear skies and low winds

Question 19

When is UHE stronger

Answer 19

In summer and when there’s an anticyclone

Question 20

What do anti cyclones cause (3)

Answer 20

1 Clear skies and low winds
2 If there is no cloud more solar radiation hits the ground
3 Low winds means warm air isn’t blown away

Question 20

Why is average wind speed usually lower in cities than in rural areas

Answer 20

The tall buildings create friction that slows down the moving air

Question 21

Why do some areas have wind speed of 0

Answer 21

They are totally sheltered from the wind by buildings

Question 22

When do you get turbulence around a building

Answer 22

1 when the wind hits the face of the building some of it is deflected down, some around the sides and some over the top

Question 23

When does a vortices (body of swirling wind occur)

Answer 23

When the wind hits the building or the ground

Question 24

What is the canyon effect

Answer 24

When powerful gusts of wind is channeled down the streets

Question 25

Give 2 reasons to explain why it rains more often in urban areas , rain is more intense and there are more thunderstorms than compared to the countryside

Answer 25

1 The UHI effect means the air in urban areas is warm which means it holds more water.
The warm moist air rises (conventional uplift)
As it rises the water vapor condenses and it rains - this is called conventional rainfall
2 urban areas generate lots of dust and pollen which float about in the air acting as a condensation nucelli - n which trigger water to condense around them. This encourages clouds to form and not allowing the warm air to disperse

Question 26

What is another effect of higher concentration of condensation nucelli in urban areas

Answer 26

Increases frequency of fog

Question 27

What is the effect of UHI on snow in urban areas

Answer 27

It doesn’t snow often and when it does it melts faster and have fewer days frost.