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, usualkly 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
