Urban Climate Flashcards
(11 cards)
Define albedo
The reflectivity of a surface.
Light surfaces reflect more than dark
What is photochemical pollution ?
Exhaust fumes and other greenhouse gases become trapped by temperature inversions, in the presence of sunlight, low-level ozone and other noxious gases form
What is temperature conversion ?
An atmospheric condition where temperature increases with height.
Don’t allow convection and trap pollution
Define urban heat island
The zone around and above an urban area which has higher temperatures than surrounding rural areas.
Why are cities warmer than rural areas ?
-Surfaces in the city tend to be much less reflective (means heat is absorbed and slowly released at night, big reflective windows concentrate heat)
-Air pollution from industries and vehicles increase cloud cover and ‘pollution dome’
-Urban areas are designed to dispose of surface water quickly (water reduces cooling by evaporation)
-Air conditioning units release hot air into atmosphere
What issues are associated with urban climate ?
-Health issues (asthma, heat stroke, organ damage)
-Higher pollution levels
-Increased strain on air conditioning
-Increased water consumption from residents
-Promote earlier flowering (trigger allergies earlier)
-Prolonged survival and reproduction of pests
What strategies are there to manage urban climate ?
-Cool surfaces
-Green roads/roofs
-Urban greening
-Cool cars/low emission
Describe precipitation in urban areas
-Rainfall can be higher over urban areas than rural areas (high temp encourages low pressure)
-Urban heat island generates convection
-Presence of high rise buildings induces air turbulence
-City pollution can increase cloud formation and rainfall
-Cities may produce large amounts of water vapour from industrial processes
-Due to low pressure caused by rising air, surface winds are drawn in from surrounding rural area
Describe thunderstorms in urban areas
-Thunderstorms develop in hot humid air, the chances of thunderstorms are increased in urban areas (especially early evening, late afternoon)
-Produced by convectional uplift under conditions of extreme instability
-Updraught of air through clouds causes rapid cooling and condensing leading to water droplets
Explain wind in urban areas
-Convectional winds can draw in strong localised winds from from cooler surrounding areas
-Wind channeling is where wind at street level is increased due to tall buildings
-Venturi effect intensifies and speed as wind is funnelled through small openings (severe gusts)
-Buildings that are widely spaced don’t do anything, more narrow causes turbulence of winds imbetween, close together wind skims over top
What are pollution reduction policies ?
Clean Air Acts
-Act of 1956 introduced smoke-free zones into urban areas
Vehicle control and public transport (London)
-ULEZ
-Hybrid and zero emission buses
-280,000 trees planted
-1500 electric vehicle charging points
-£48 million scrappage fund for polluting cars is in place
