Urban Climate

Question 1

What is the urban heat island effect

Answer 1

Urban areas being warmer then rural areas

Question 2

What are urban heat islands

Answer 2

Urban areas w higher air temperatures than the surrounding rural areas eg in London

Question 3

Where are the highest temperatures found

Answer 3

Industrial areas and the most built up eg the CBD

Question 4

What are temperature sinks

Answer 4

There are pockets of cool air above parks and bodies of water (eg rivers or ponds)

Question 5

What are temperature plateaus

Answer 5

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

Question 6

What are temperature cliffs

Answer 6

Temperature can change rapidly when land use changes (eg from inner city housing to CBD, high rise buildings)
Rapid changes are referred to as temperature cliffs

Question 7

6 ways in which urban climate issues can be managed

Answer 7

Green roofs t

Urban greening t

Cool cars t

Building design w

Laws

Public transport

Question 8

How do green roofs manage urban climate

Answer 8

Not dark so doesn’t absorb heat

Vegetation stores water so when it transpires it takes energy out of the air

Consists of a growing medium planted over a waterproof membrane

It can reduce rainwater run off

Can increase urban biodiversity by providing habitat space for birds and small animals

Question 9

How does urban greening manage urban climate

Answer 9

Planting trees and vegetation gives shade- surface peak temp reductions of 5-2 degrees may be possible

It can have a national cooling effect as seen by lower temp in urban parks around the world

Urban trees act as urban stores and can reduce urban flooding by intercepting rainfall and filters pollutants from the air

Question 10

How do cool cars manage urban climate

Answer 10

Lighter coloured car shell reflects more sunlight then dark car shades

This cools the inside and reduces need for air conditioning

Cars in cities contribute significantly to higher temp and pollution levels experienced there

SO use of cool cars benefit city and driver

Question 11

How do building designs- the Burj Khalifa Tower

Answer 11

828m tallest building in the world

Concern- windstress and wind vortexes pulling building side to side

Has to withstand gusts of over 240km/hour

Series of aerodynamics improvements had to be made to ensure building can withstand this

Soften edges of building deflect wind around the structure and prevents forming whirlpools/vortexes

The entire tower orientated relative to prevailing wind directions

Sways slowly back and forth about 2m at very top- but doesn’t suffer like skyscrapers in the past

Question 12

How do laws manage urban climates

Answer 12

Clean air acts

Introduced smoke free zones into urban areas and this policy slowly began to clean up the air

1990- tough regulations imposed on levels of airborne pollution, particularity on PM10s

Local councils in UK now require to monitor pollution in their areas and to establish air quality management
Areas where= likely to be exceeded

London air quality standards improved

2015- NOx emissions still higher then UK and a European law recommended

Measures introduced to clean up 12% of NOx emmisions

More dust suppressants at industrial sites

Question 13

How does public transport manage urban climate

Answer 13

ULEZ (ultra low emission zone) introduced 2020

Exhaust emission standards set and daily non compliance charge introduced to encourage cleaner vehicles to drive around London

Double decker buses operating in central London=hydbrid and all single deck- 0 emission

Question 14

What are the 4 main causes of the UHI effect (these are greater in urban areas)

Answer 14

Absorption of heat by urban surfaces (urban- darker)

Air pollution

Heat from human activity

Less evapotranspiration

Buildings

Industry

Car friction

Rapid urban drainage

Question 15

Explain how absorption of heat by urban surfaces is a cause of UHI

Answer 15

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

They slowly release the heat as long wave radiation

This is most noticeable at night when it warms the air

Urban surfaces also have low albedo- they absorb more energy rather then reflecting it

Question 16

How does air pollution cause UHI

Answer 16

Air pollution from cars and factories increased cloud cover over the city

It also creates a ‘pollution dome’ - a layer of pollution over the city

Both these things trap ongoing heat radiation and reflect it back to the surface

Question 17

How does heat from human activity cause UHI

Answer 17

Cars factories offices central heating etc and people all release heat

Question 18

How does less evapotranspiration cause UHI

Answer 18

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 evapotranspiration means higher temperatures

Question 19

How does the UHI effect vary between day and night

Answer 19

The UHI effect is stronger at night
Urban day time temperatures are on average 0.6 degrees Celsius warmer then the surrounding rural areas, but at night time the temperatures can be 3-4 degrees warmer

This is because rural areas cool down at night but urban areas don’t cool as much because urban surfaces continue to release heat that they’ve absorbed during the day

Question 20

How does the UHI effect vary seasonally

Answer 20

It’s stronger in Summer (in madlutitude cities like Lon)

Average winter temperature can be up to 2 degrees warmer but in summer up to 5 degrees warmer

This is because there is more solar radiation in summer, so urban areas absorb more heat

Question 21

How do anti cyclones affect the UHI effect

Answer 21

It’s stronger when there’s an anticyclone

They cause clear skies and low winds

If there are no clouds, more solar radiation reaches and heats the ground

Low winds means warm air isn’t blown away

Question 22

Why is average wind speed lower in cities then rural areas

Answer 22

Tall buildings create friction that slows down the moving air

Question 23

Where are wind speeds O

Answer 23

Areas that are totally sheltered from wind by buildings

Question 24

Explain wind vortexes

Answer 24

You get turbulence around buildings

This happens when wind hurts the face of a building- some it’s deflected down, some around the sides and some over the top

When these winds hit other buildings or the ground they cause vortexes (bodies of swirling air)

Question 25

What is the canyon effect

Answer 25

You gg powerful gusts of wind when wind is channeled down streets

This is known as the canyon effect and affects the planning of buildings

Question 26

Where does it rain more and more intensely

Answer 26

Urban

Question 27

Why does it rain more and more intensely in urban areas (2)

Answer 27

The UHI effect means the air in urban areas is warm and warm air can hold more water
The warm moist air rises- this is called convection uplift
As it rises, it cools, the water vapour condensed and it rains- convection rainfall

Urban areas generate huge amounts of dust and pollution.
Particles of dust and pollution floating about in the air acts as condensation nuclei (the trigger water to condense around them)
This encourages clouds to form, rather than allowing the warm, moist air to disperse

V rapid warmer n and rising leads to formation of thunderstorms

Question 28

Where is their more fog and why

Answer 28

Urban areas

As there’s a higher concentration of condensation nuclei

Question 29

Where is there more snow and fog and why

Answer 29

More in rural areas and lesss in urban areas

Snow melts faster in urban area

This is because it is warmer due to UHU effect

Also why fewer days of frost

Question 30

How does wind speed differ in rural and urban areas

Answer 30

Wind on average 30% lower in urban places

However, there are heat variations in wind speeds within an urban environment caused by the alignment, height and distribution of urban buildings

Question 31

What is the wind break effect

Answer 31

Some urban places are v sheltered from effects of the wind

Question 32

What is the ventuin effect

Answer 32

Violent gusting as air is forced through narrow gaps and air pressure is reduced

Question 33

How many more clouds are in urban places

Answer 33

10%

Question 34

Percentage more of pollutants in urban places

Answer 34

10X more nitrous dioxide- causing respiration problems and acid rain

200X more sulphur dioxide (same as above)

2X more Co2- contributes to climate change

10X more hydro carbons cause heart problems, headaches and tiredness

More diesal particulates cause respiratory problems and dirty buildings