Lesson 16-Urban Climates Flashcards
How do urban areas affect their climate?
- 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
Effect of urban area on precipitation
- Quantity of rain- 5-10% increase
- Days with less than 5mm of rain- 10% increase
- Snowfall in inner city- 5-10% increase
Reasons for higher rainfall in urban areas
- 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
Effect of urban area on thunderstorms
- Annual mean humidity- 6% decrease
- Winter-2% decrease of humidity
- Summer- 8% decrease of humidity
-due to how thunderstorms are related to the levels of convection and not the humidity
Why are there more thunderstorms in urban areas?
- 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
Effect of urban environment on fog
- Fog visability in winter- 100% increase
- Fog visability in summer- 30% decrease
-due to cool surfaces in winter allowing evaporated water to condense
Why is fog linked to industrialisation?
- The average number of particles act as condensation nuclei and encourage fog formation at night, usually under high pressure weather conditions
-New Delhi and Beijing suffer regular winter fogs
Smog
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
Photochemical smog
- 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
Temperature inversion
- An atmospheric condition in which temperature, unusually increases with height
-doesnt allow air to rise>traps in pollution in lower sections of air
CASE STUFY URBAN SMOG/AIR POLLUTION-Ulaanbaatar,Mongolia
- 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
Effects of poor air quality in Ulaanbaatar, Mongolia?
- 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
How does a grid iron street pattern have an affect on winds?
- Chicago suffer from more intense urban winds due to channeling affect and venturi affect
Responses to the poor air quality issue in Ulaanbaatar, Mongolia?
- Extended school winter holidays
- Masks
- Technology to measure the air quality-costs a lot for the general public
- Supply of air canisters
How does a medeival street pattern have an affect on winds?
- European cities like London dont feature straight lines and therefore dont suffer from as intense winds due to more friction
Channeling effect
the flow of winds in straight lines typically in grid iron street patterns
Venturi effect
the compression between buildings causes winds to tunnel faster
Effect of an urban area on windspeed?
- Annual windspeed- 20-30% decrease>due to barriers in urban areas
- Calms- 5-20% increase
- Extreme gusts- 10-20% increase
The three main effects of wind in urban areas
- 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
Example of skyscraper causing intense urban winds
- Brdigewater Place, Leeds
- In 2011, a man was killed after intense winds blew a lorry onto him
- speeds between 67 and 79mph
