booklet 10 - urban climate

• What are microclimates?


  the small scale variations in temperature, precipitation, humidity, evaporation and wind speed that occur in a particular environment
• factors effecting microclimates


  - temperature

  - humidity

  - precipitation

  - wind speed

  - evaporation
• How are urban and rural climates different?

  Cooler in a rural areas as well as higher wind speeds due to more exposure, humidity is higher in rural areas

  More rainy in urban areas due to evaporation by heat and then cooling and condensing, hotter in urban areas due to urban heat island effect
• The Urban Climate Dome

  Warmer air forms a dome or plume over the city. The urban canopy layer (UCL) is the layer of air closest to the surface in cities. Above the UCL lies the urban boundary layer (UBL). The UBL forms a dome of warmer air that extends downwind of the city.
• urban heat island effect

  describes how temperatures are highest towards the centre and decrease towards the suburbs. Closer to the buildings the hotter it is
• When is the UHE most noticeable

  The urban heat island effect is stronger at night with temps being 3-4 degrees warmer. Urban day time temps are 0.6 degrees warmer than rural areas near by

  Stronger in the summer and when there is anti cyclones because warm air isn't blown away and there are no clouds. More solar radiation reaches the ground
• Albedo


  The measure of the reflectivity of a surface - when applied to the earth its the measure of how much of the suns energy is reflected back to space
• Highest and lowest albedos

  Tarmac - 0.10

  Grass - 0.25

  white paint - 0.80
• Factors influencing urban heat isalnd effect

  Anthropogenic heat - heat that is generated by human activity from sources like buildings, cars people and industrial processes
• how does the UHE impact peoples lives

  - uncomfortable in public transport when it is hot

  -causes of heat stroke and asthma and organ damage is much higher in the uhe

  - excessive heat puts increased demand onm energy use

  - higher pollution levels due to hot and still anti cyclonic weather

  - increased water consumption - strain on locals and businesses
• Ways to manage urban climate

  dynamic shades - open and close to keep the heat of the buildings (Abu Dabo)

  Painting roads white to redice the temps by 9.4 degrees ( LA)

  Cool surfaces, green roofs and urban greenery help to reduce the uhe

  planting more vegetation - provides shade and evapotranspiration reduced temps (Singapore temps dropped by 2-3 degrees

  Water misters in china to spray people

  In Sydney water features added to reduce temps by 10 degrees
• Causes of poor air qauility

  road transport responsible for 90% carbon monoxide emissions and 50 percent emissions of nitrogen oxide
• Particulate air pollution


  come from power stations and vehicle exhausts

  small bits of rubber and metal from engine wear
• Great smog 1952


  4000 people died as a result of the fog

  many suffered from breathing problems

  travel disrupted

  laws bought in to avoid repeat of event
• Clean air acts - success?

  acts banned emissions of black smoke and decreed residents of urban areas and operators of factories must convert to smokeless fuels
• photochemical pollution and causes

  photochemical smog is caused as above normal levels of nitrogen oxide and ozone are produced when pollution and sunlight react
• Zoning indsutry


  industry located downward in cities if possible and factories forced to build chimneys that go above inversion layer
• Technical innovations


  hybrid electric plug in hybrids and fully electric vehicles reduce emissions

  filters to reduce gas and particle emissions
• London air quality case study
• clean air acts


  tough regulations to reduce airborne pollution

  act of 1956 introduced smoke free zones into urban areas which helped to slowly clean up the air
• vehicle control and public transport

  increased provision of public transport

  ULEZ introduced sep 2020

  exhaust emissions standards and daily non compliance charge intoroduced
• urban transport solutions


  creation of bus or car pooling lanes

  congestion charge introduced

  road schemes such as urban bypasses

  park and ride

  greater use of waterways for transport eg uber boats

  strategies such as banning cars from driving on certain days and alternating between cars with liscense plates and in even or uneven numbers