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Flashcards in Urban Climate Deck (34):

What is the urban heat island effect

Urban areas being warmer then rural areas


What are urban heat islands

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


Where are the highest temperatures found

Industrial areas and the most built up eg the CBD


What are temperature sinks

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


What are temperature plateaus

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


What are temperature cliffs

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


6 ways in which urban climate issues can be managed

Green roofs t

Urban greening t

Cool cars t

Building design w


Public transport


How do green roofs manage urban climate

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


How does urban greening manage urban climate

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


How do cool cars manage urban climate

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


How do building designs- the Burj Khalifa Tower

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


How do laws manage urban climates

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


How does public transport manage urban climate

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


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

Absorption of heat by urban surfaces (urban- darker)

Air pollution

Heat from human activity

Less evapotranspiration



Car friction

Rapid urban drainage


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

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


How does air pollution cause UHI

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


How does heat from human activity cause UHI

Cars factories offices central heating etc and people all release heat


How does less evapotranspiration cause UHI

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


How does the UHI effect vary between day and night

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


How does the UHI effect vary seasonally

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


How do anti cyclones affect the UHI effect

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


Why is average wind speed lower in cities then rural areas

Tall buildings create friction that slows down the moving air


Where are wind speeds O

Areas that are totally sheltered from wind by buildings


Explain wind vortexes

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)


What is the canyon effect

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


Where does it rain more and more intensely



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

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


Where is their more fog and why

Urban areas

As there’s a higher concentration of condensation nuclei


Where is there more snow and fog and why

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


How does wind speed differ in rural and urban areas

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


What is the wind break effect

Some urban places are v sheltered from effects of the wind


What is the ventuin effect

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


How many more clouds are in urban places



Percentage more of pollutants in urban places

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