Urban Microclimates I can define and apply the concept of an urban heat island I can identify reasons for an issues stemming from urban air pollution I can identify other issues of urban microclimates such as annual rainfall and wind gusts. 1

Urban Heat Island An effect in large cities that causes the city to be warmer then the surrounding countryside 2

This causes the UHI to be most evident at night Causes of UHI 1 Materials: Dark roofs and asphalt absorb heat during the day and slowly release it at night. This causes the UHI to be most evident at night 3

Causes of UHI 2. People: Factories, buildings and people in general give off heat. The more buildings and people, the more heat given off. 4

Causes of UHI 3. Lack of evaporation: Evaporation causes cooling. In an area with few plants and lots of non-porous surfaces. Instead of evaporating slowly, most of the water becomes run-off and moves into sewers and storm drains. 5

Problems caused by UHI Heat Stroke: Excessive heat can kill, especially the elderly and young children and those without access to AC. This happens more in urban areas because due to UHI there is no relief from the heat at night. Greater use of cooling systems in the summer = more energy used 6

Fixing UHI Green roofs Green space in urban areas Different materials used for roads and buildings

Urban Air Pollution Two Major Factors: 1. Quantity of pollution -more in LEDC than MEDC, why? 2. Wind dispersal

Causes of Urban Air Pollution Cars and other transportation Soil erosion (loess in Beijing) Burning of fossil fuels ESPECIALLY coal!

Beijing Biggest cause is coal during heating season Season is highly regulated by the government to control some of this Adds soot sulpher dioxide to the air Worse when high pressure zone keeps pollution near the surface

Beijing: Secondary Causes More Cars Soil Erosion Areas around the city are clay which erodes to a fine dust and blows over the city Some of the problem has been solved by planting trees around the city. Industry Benzopyrene, a lung-cancer causing chemical, is released from some factories Factories do not have the emission controls standards like factories in the US.

Los Angeles Biggest cause is cars and transportation Urban sprawl means few people live near work Poor public transit system This causes photochemical smog Gases from car exhaust get trapped and heated by strong sunlight forming a brown fog. Hot, dry environment with little wind makes this worse

Solving LA Air Pollution South Coast Quality Air Management District Made and enforced car and factory emissions regulations Public programs to encourage car-pooling Public programs to encourage 0 pollution cars (electrics)

UHI and Rainfall The extra heat can cause upward movement in the atmosphere which can lead to more storm activity Local low pressure during the day keeps damp air trapped causing more cloud formation Overall, cities tend to have higher rainfall averages than surrounding areas.

Urban Wind Urban topography can both increase and decrease wind. On the surface, tall buildings can create “urban canyons” which cause wind to gust through these areas. This often causes litter and fine particles of dirt and soot to blow around the area on dry days.

Urban Wind Urban topography can both increase and decrease wind. Overall, cities often have LESS wind in the atmosphere due to tall buildings blocking and slowing down wind speed. This keeps winds from dispersing pollution or cooling the UHI