Urban Climate

Question 1

What is the phenomenon that makes urban areas hotter called?

Answer 1

Urban heat island effect (UHI)

Question 2

Where are the highest temperatures found in urban areas?

Answer 2

Industrial areas and the most densely built up areas (CBD).

Question 3

Where are temperature sinks found and what are they?

Answer 3

Pockets of cool air usually found above parks and bodies of water.

Question 4

What is a temperature plateau?

Answer 4

Areas within the city with the same land use that generally have the same temperature.

Question 5

What causes temperature change rapidly in urban areas?

Answer 5

When land use changes. Eg: from housing to high rise buildings.

Question 6

What is a temperature cliff?

Answer 6

Rapid changes in temperature in urban areas.

Question 7

What are the 4 main reasons for the UHI effect?

Answer 7

-Absorption of heat by bean surfaces.
-Air pollution
-Heat from human activity
-Less evapotranspiration

Question 8

How does absorption of heat by urban surfaces cause the UHI effect?

Answer 8

Concrete surfaces absorb and store heat from the sun during the day and slowly release it as long wave radiation.

Question 9

How does air pollution cause the UHI effect?

Answer 9

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

Question 10

How does heat from human activity cause the UHI effect?

Answer 10

Cars, factories and people themselves all release heat.

Question 11

How does less evapotranspiration cause the UHI effect?

Answer 11

Water is removed by drainage systems so there is little surface water to evaporate.
Not much vegetation so there is little transpiration.
=higher temperatures

Question 12

How is the UHI effect different in the night?
Why?

Answer 12

Stronger at night:
Night time temperatures are 3-4 degrees warmer than average.
Urban surfaces continue to release heat they’ve absorbed during the day.

Question 13

How does the UHI effect vary seasonally?why?

Answer 13

Stronger in the summer:
Average summer temperature 5 degrees warmer.
There is more solar radiation in summer so urban areas absorb more heat.

Question 14

What do anti cyclones do and how does this affect the UHI effect?

Answer 14

Cause clear skies and low winds so more solar radiation reaches and heats the ground. Low winds means hot air isn’t blown away.

Question 15

What is the wind speed like in urban areas compared to rural areas?

Answer 15

Lower in cities.

Question 16

Why is average wind speed different in urban areas?

Answer 16

Because tall buildings create friction which slows down moving air.
Wind speed can even become 0 when areas are completely sheltered by buildings.

Question 17

Why do you get turbulence around buildings?

Answer 17

When wind hits the face of the building, some is deflected down some around the sides and some over the top.

Question 18

What is a vortices?

Answer 18

When wind hits other buildings they cause vortices which are swirling bodies of air.

Question 19

What is the canyon effect?

Answer 19

Powerful gusts of wind when wind is channeled down streets.

Question 20

Why is rain and thunderstorms more common in urban areas?

Answer 20

-UHI effect causes urban air to be warm. Warm most air rises and as it cools the vapour condenses and it rains.
-Urban areas generate lots of dust and pollution which trigger water to condense around them encouraging clouds to form.

Question 21

What is condensation nuclei?

Answer 21

When particles of dust and pollution trigger water to condense.

Question 22

What type of rainfall occurs in urban areas?

Answer 22

Convectional rainfall

Question 23

Why is there less snow in urban areas?

Answer 23

UHI effect makes it warmer so snow melts faster.