Urban microclimates

What is a microclimate?

the distinctive climate of a small-scale area, such as a city or neighbourhood

What are the two levels within urban microclimate domes?

• the urban canopy layer

• the urban boundary layer

Do urban areas have more or less trees than surrounding rural areas?

cities (urban areas) have fewer trees than surrounding rural areas

Do urban areas experience more or less frosts than rural areas?

urban areas experience 2–3 weeks fewer frosts than rural areas

What is the urban canopy layer?

the layer of air below roof level where processes occur between buildings

What is the urban boundary layer?

the layer above roof level that extends downwind into surrounding rural areas

What effect do dark rooftops and pavements have on urban microclimates?

• absorb more solar radiation

• increase urban temperatures

Do urban areas have higher or lower relative humidity than rural areas?

urban areas have lower relative humidity than rural areas

How much more cloud cover do urban areas typically have compared to rural areas?

approx. 5–10% more cloud cover

What effect do tall buildings have on urban microclimates?

• absorb and reflect solar radiation

• increase temperatures

How does poor building insulation affect urban microclimates?

• releases heat at night

• contributes to the urban heat island effect

What is the urban heat island (UHI) effect?

when urban areas are 2–5°C warmer than surrounding rural areas

What is a temperature sink?

a cooler area within a city, often above parks or water bodies

What is a temperature cliff?

a rapid temperature change between different land uses

Do urban areas have a smaller or larger diurnal temperature range than rural areas?

urban areas have a larger diurnal temperature range than rural areas

What causes increased cloud cover in urban areas?

a higher concentration of condensation nuclei from pollution

Do urban areas increase or decrease thunderstorm frequency?

increase by approx. 25%

What is the canyon effect?

wind is channelled between buildings, increasing speed

What are vortices?

swirling air created as wind flows around buildings

What is photochemical smog?

pollution formed when sunlight reacts with chemicals in the atmosphere

Are urban wind speeds generally higher or lower than rural wind speeds?

wind speeds are usually lower in cities (urban areas) due to obstacles

What are photocatalytic materials?

materials that use sunlight to break down pollutants

What is a smog-free tower?

a structure that removes polluted air and releases cleaner air

Are self-driving cars expected to worsen or improve fuel efficiency?

may improve efficiency by 15–40%

What is a congestion charge?

a fee for driving in certain areas to reduce traffic and pollution

What is “park and ride”?

parking outside a city and using public transport into the centre

What is the purpose of the MOT emissions test?

ensure vehicles meet emission standards

What was the purpose of the UK Clean Air Acts (1956 & 1968)?

to reduce air pollution

What did the UK Clean Air Acts (1956 & 1968) create?

smoke-free zones

What does IPPC stand for?

Integrated Pollution Prevention and Control

What is IPPC?

a system regulating industrial emissions

What is radiative fog?

fog formed by the radiative cooling at the surface during long, clear, cold nights with light winds

What is advection fog?

fog formed when warm, moist air moves horizontally over a cold surface