Urban climates

Question 1

How does precipitation differ?

Answer 1

Rains 5-15% more, and thunderstorms are 25% more common.

Humidity is 6% lower as less evaporation. (amount of moisture in the air)

Question 2

How does wind speed differ?

Answer 2

30% lower in urban areas but there are greater variations in wind speed.

Question 3

Why does wind speed differ?

Answer 3

1. Greater friction caused by buildings
2. ‘Wind break’ effect means certain areas are sheltered from the wind.
3. ‘Canyon effect’ means wind is forced down streets with high buildings.
4. ‘Venturi effect’ is violent gusting effect as air is forced through narrow gaps

Question 4

How does visibility differ?

Answer 4

There is up to 10% more cloud so visibility is a lot lower. There is also a lot of smog and photochemical smog which is a reaction between sunlight and pollution.

Question 5

Ways urban climates can be managed?

Answer 5

1. Green roofs
2. Urban greening
3. Cooler cars
4. Building designs
5. New laws
6. Increase in public transport

Question 6

Why does precipitation differ?

Answer 6

1. More condensation nuclei, these cause water droplets to form.
2. Warm buildings and cars cause air to rise and eventually condensate.
3. Rapid warming and rising leads to creation of thunderstorms.

Question 7

What is the urban heat island effect?

Answer 7

Urban areas are now commonly warmer than the surrounding rural area. Highest temperatures are in the CBD and are also more noticeable at night (day = 2° higher, night = 5° higher)
Caused by-
1. High absorption of heat by urban surfaces, dark surfaces absorb more heat e.g. Tarmac and concrete. Slowly release at night which is when temps noticeably rise.
2. Air pollution from cars + factories is higher increases cloud which reduces outgoing heat radiation.
3. Heat from human activity e.g. Offices, central heating, lights.
4. Less evapotranspiration which uses heat energy so less means higher temperatures.

Question 7

London case study (urban air quality)

Answer 7

London’s ecological footprint is 2x size of the U.K. / 6.6 GHA.

Causes of the problems:

1. Nitrogen dioxide levels regularly breach EU limits.
2. Diesel vehicles are most commonly used e.g. Buses, Lorries.
3. High levels of photochemical smog due to factories and pollutants

Impacts of the problems:

1. High levels of photochemical smog
2. 5.3% of all deaths could be linked to air pollution and in central London up to 8.3%
3. 802 schools in areas where EU limit of 40 micrograph per cubic metre is exceeded

How’s it being managed:

• Clean air acts
• LEZ and ULEZ (must meet minimum emissions standards or must pay a charge to drive)
• Encouraged use of Boris bikes and more pedestrianised zones
• Congestion charges operating in central London on top of ULEZ