Urban Climate

Question 1

What is the urban heat island effect?

Answer 1

The phenomenon of urban areas being warmer than rural areas

Question 2

What is an urban heat island?

Answer 2

Urban areas with higher air temperatures than. the surrounding rural areas

Question 3

Where are the highest temperatures found?

Answer 3

Industrial areas and in the most densely built up areas like the 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 temperature plateaus?

Answer 5

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

Question 6

When does temperature change rapidly. - what are these called?

Answer 6

When land use changes. Rapid changes are called cliffs

Question 7

What are the 4 main causes of the UHI effect?

Answer 7

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

Question 8

How does absorbing heat from urban surfaces work?

Answer 8

Concrete, brick and tarmac surfaces absorb and store heat from the sun during the day

Question 9

How does heat get released (AOHUS)

Answer 9

They slowly release heat as long wave radiation - this is more noticeable at night, when it warms the air

Question 10

How does air pollutiony cause the UHI effect?

Answer 10

Air pollution from cars and factories increases cloud cover over a city creating pollution dome. They trap outgoing heat radiation and reflect it. back to the surface

Question 11

How does heat from human activity cause the UHI effect?

Answer 11

Cars, fcatories, offices, central heating, air conditioning units and people themselves all release heat

Question 12

How does less evapotranspiration cause the UHI effect?

Answer 12

When it rains the water is quickly removed by drainage systems, so there’s little surface water to evaporate. Also there isn’t much vegetation, so there’s little transpiration. Evapotranspiration uses heat energy so less of it means higher temperatures

Question 13

When is the UHI effect stronger

Answer 13

AT night

Question 14

What are urban temperatures like compared to rural areas

Answer 14

In the day they’re 0.6 warmer, but at night they’re 3-4 warmer

Question 15

Why are urban areas hotter than rural areas especially at night?

Answer 15

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

Question 16

Whys the UHI stronger in the summer?

Answer 16

Average winter temperatures can be 2 warmer, but average summer temperatures can be up to 5 warmer. This is because there’s more solar radiation summer, so urban areas absorb more heat

Question 17

When is the UHI stronger?

Answer 17

When there’s an anticyclone

Question 18

What do anticyclones cause?

Answer 18

Clear skies and low wind

Question 19

What happens if there’s no clouds when there’s anticyclones?

Answer 19

More solar radiation reaches and hits the ground. low winds mean warm air isn’t blown away

Question 20

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

Answer 20

Because tall buildings create friction that slows down moving air - some areas have a wind speed of 0

Question 21

Why do you get turbulence around buildings?

Answer 21

When the wind hits the face-off a building - some of its deflected down, some around the sides and some over the top

Question 22

What happens when winds hit other buildings. or the ground?

Answer 22

They cause vortices

Question 23

What are vortices?

Answer 23

Bodies of swirling air

Question 24

WHta is the canyon effect?

Answer 24

You get powerful gusts of wind when wind is channelled down streets

Question 25

What is rain like in urban areas in comparison to the countryside?

Answer 25

It rains more often and it’s more intense there’s also more thunderstorms

Question 26

What are the 2 reasons that there’s more rain and thunderstorms

Answer 26

• The UHI effect means that air in urban areas is warm and warm, moist air rises. As it rises it cools, the water vapour condenses and it rains
• Urban areas generate huge amounts of dust. and pollution. Particles of dust and pollution floating about in the air act as condensation nucelli. This encourages clouds to form rather than allowing warm moist air to disperse

Question 27

What type of rain is in urban areas?

Answer 27

Convectional

Question 28

What is a convectional uplift

Answer 28

Warm moist air rises

Question 29

What increases the frequency of fog?

Answer 29

the higher concentration of condensation nucelli

Question 30

WHy doesn’t it snow as. often in urban areas?

Answer 30

Its warmer because of the UHI effect