Lesson 16-Urban Climates

Question 1

How do urban areas affect their climate?

Answer 1

• Urban areas create their own set of local atmospheric conditions
  -temp,precipitation,humidity,visability,air quality and wind speeds that differ from those in the surroudning rural areas
  -urban microclimate

Question 2

An urban microclimate

Question 3

Effect of urban area on precipitation

Answer 3

• Quantity of rain- 5-10% increase
• Days with less than 5mm of rain- 10% increase
• Snowfall in inner city- 5-10% increase

Question 4

Reasons for higher rainfall in urban areas

Answer 4

• Urban heat islands generate convection(air rising)-increase in heated ground surfaces, rapid evapotranspiration
• High rise buildings and mix of heights induces air turbulance
• City pollution can increase and cloud formation and rainfall-pollutants act has hydroscopic nuclei and assist raindrop formnation

Question 5

Effect of urban area on thunderstorms

Answer 5

• Annual mean humidity- 6% decrease
• Winter-2% decrease
• Summer- 8% decrease

Question 6

Why are there more thunderstorms in urban areas?

Answer 6

• Thunderstorms are produced by convectional uplift under coditions of extreme instability
• Cumulonimbus clouds may develop up to the hight of the tropapause, where the inversion produces stability

Question 7

Effect of urban environment on fog

Answer 7

• Fog visability in winter- 100% increase
• Fog visability in summer- 30% decrease

-due to cool surfaces in winter allowing evaporated water to condense

Question 8

Why is fog linked to industrialisation?

Answer 8

• The average number of particles act as condensation nuclei and encourage fog formation at night, usualkly under high pressure weather conditions
  -New Delhi and Beijing suffer regular winter fogs

Question 9

Smog

Answer 9

Airbourne pollution which is a mixture of fog an smoke particles which become concentrated in the air from industry and transport
-caused by a temp inversion

Question 10

Photochemical smog

Answer 10

• Caused by reactions between sunlight and atmospheric pollutants such as hydrocarbons

-often invisible but can be very harmful, with it being responsible each year for elevated rates of death and illness

Question 11

Temperature inversion

Answer 11

• An atmospheric condition in which temperature, unusually increases with height

-doesnt allow air to rise>traps in pollution in lower sections of air

Question 12

CASE STUFY URBAN SMOG/AIR POLLUTION-Ulaanbaatar,Mongolia

Answer 12

• Burning raw coal
• Lack educatuion around poor air quality and how to reduce the impacts
• High alttitude and land locked-thin air, lack of sea brease
• Rural to urban migration

Question 13

Effects of poor air quality in Ulaanbaatar, Mongolia?

Answer 13

• Affects weather patterns, agriculture failures lead to farmers migrating to city
• Mongolia has warmed by 2.2 degrees celcius
• 270-300 children hospitalised a day due to PM 2.5

Question 14

How does a grid iron street pattern have an affect on winds?

Answer 14

• Chicago suffer from more intense urban winds due to channeling affect and venturi affect

Question 14

Responses to the poor air quality issue in Ulaanbaatar, Mongolia?

Answer 14

• Extended school winter holidays
• Masks
• Technology to measure the air quality-costs a lot for the general public
• Supply of air canisters

Question 15

How does a medeival street pattern have an affect on winds?

Answer 15

• European cities like London dont feature straight lines and therefore dont suffer from as intense winds due to more friction

Question 16

Channeling effect

Answer 16

the flow of winds in straight lines typically in grid iron street patterns

Question 17

Venturi effect

Answer 17

the compression between buildings causes winds to tunnel faster

Question 18

Effect of an urban area on windspeed?

Answer 18

• Annual windspeed- 20-30% decrease>due to barriers in urban areas
• Calms- 5-20% increase
• Extreme gusts- 10-20% increase

Question 19

The three main effects of wind in urban areas

Answer 19

• On clear night when the urban heat island effect is at its greatest, convectional processes can draw in strong localised wind from cooler surrounding areas
• Clusters of high-rise buildings increase the channeling effect>enduces discomfort
• Buildings widely spaced they act as blocks of the wind but if they are closer together then the skimming effect occurs

Question 20

Example of skyscraper causing intense urban winds

Answer 20

• Brdigewater Place, Leeds
• In 2011, a man was killed after intense winds blew a lorry onto him
• speeds between 67 and 79mph