urban microclimates

Question 1

what are the two levels in a climatic dome?

Answer 1

urban canopy below roof level and the urban boundary layer above

Question 2

features of climatic domes

Answer 2

temperature ranges, precipitation generation and patterns, humidity, wind speeds, reduced visibility

Question 3

what is the urban heat island?

Answer 3

a significantly warmer ‘island’ surrounded by a rural ‘sea’ of cooler temperatures

Question 4

what are the reasons for an urban heat island?

Answer 4

urban areas have lower albedo as dark surfaces e.g tarmac absorb heat during the day and release it slowly at night
large expanses of glass and steel reflect heat
less evapotranspiration and drains remove water quickly so moisture in the air is reduced, less heat energy lost in evaporating it
buildings ‘leak’ heat through poor insulation in winter and air conditioners pump hot air into the streets in summer
power stations, industries, vehicles and inhabitants generate heat

Question 5

thermal gradient

Answer 5

the temperature decline from urban centre to rural-urban fringe, 6 degrees in summer and 2 degrees in winter

Question 6

how does urban air pollution help the formation of clouds?

Answer 6

results in more condensation nuclei

Question 7

fog

Answer 7

thicker and persist longer in anticyclonic (high pressure) conditions where winds are too weak to blow them away

Question 8

fog in the industrial revolution

Answer 8

19th century- an increase in the number of days of winter fog associated with the burning of coal

Question 9

thunderstorms

Answer 9

urban convection is powerful in summer, rising heat can rise quickly in the atmosphere and trigger heavier and frequent late afternoon and evening thunderstorms. air cools and condenses rapidly, forms water droplets which charge the thundercloud and discharge as lightning

Question 10

wind

Answer 10

urban structures interfere with wind by slowing, redirecting and disturbing overall airflow. they create friction and act as windbreaks, urban mean annual velocities are up to 30% lower in urban areas.

Question 11

impacts of airflow, turbulence and emissions

Answer 11

urban canyons- narrow streets bordered by high rise buildings funnelling and concentrating winds
venturi effect- a violent form of wind in narrow gaps by air rushing to replace low pressure vortices beyond structures