Weather in cities

Question 1

Temperature in cities

Answer 1

• buildings retain and release heat more strongly than in rural areas
• temperatures are higher
• tarmac surfaces are heated intensely and then strongly heat the air above it

Question 2

Winds in cities

Answer 2

• winds can be channelled between high-rise buildings increasing velocities
• buildings also act as windbreaks, reducing velocities

Question 3

Sunlight in cities

Answer 3

• actual sunlight amounts are lower
• high-rise buildings block out light
• high amounts of dust reflect and absorb sunlight

Question 4

Precipitation in cities

Answer 4

• greater amounts than in other locations

- concentrate surfaces lead to convection currents and cloud formation

Question 5

Humidity in cities

Answer 5

-lower in urban areas as higher temperatures can hold greater amounts of water vapour

Question 6

Clouds in cities

Answer 6

-thicker and more frequent

Question 7

The percentage of reflected insolation is…

Answer 7

1.9 per cent in rural and 0.4 per cent in urban areas(a lot of is absorbed).

Question 8

Anthropogenic heat is…

Answer 8

heat released by human activity(driving, industry). Some cities in colder areas can release more heat from human activity than the area receives from the sun.

Question 9

The percentage of outgoing infrared is…

Answer 9

8.5 per cent in rural and 10.3 per cent in urban areas.

Question 10

Outgoing infrared is also called…

Answer 10

terrestrial radiation.

Question 11

The percentage of storage heat is…

Answer 11

0.3 per cent in rural and 1.3 in urban areas.

Question 12

Asphalt albedo

Answer 12

5-20 per cent

Question 13

Concentrate albedo

Answer 13

10-35 per cent

Question 14

White paint

Answer 14

50-90 per cent

Question 15

Coloured paint

Answer 15

15-35 per cent

Question 16

Grass albedo

Answer 16

25-30 per cent

Question 17

The percentage heat loss due evaporation is

Answer 17

24 per cent in rural and 1 per cent in urban areas(water is stored mainly underground)

Question 18

The percentage of heat given up by the ground at night is…

Answer 18

twice the amount as in the rural areas.

Question 19

There is temperature…

Answer 19

inversion in urban areas at some point. (ground is colder than the air above)

Question 20

In which ways the urban area modifies the climate?

Answer 20

• wind speeds
• temperature
• clouds and precipitation
• pollution

Question 21

The greater the urban area…

Answer 21

the greater the modification of a climate will be.

Question 22

Winds in urban areas are modified:

Answer 22

• lower speeds
• greater variability
• large-scale convection

Question 23

Winds lower speeds

Answer 23

• have lower wind speeds on average per cent less in the city centre
• due to the roughness of the land surface(different heights of buildings), which increases the surface friction

Question 24

Greater variability of winds in urban areas

Answer 24

• due to layout and height of the buildings
• urban canyons
• venturi effect

Question 25

Urban canyons

Answer 25

Straight streets lined with tall buildings can produce it. This funnel wind down them producing high velocities thanks to the venturi effect.

Question 26

Venturi effect

Answer 26

It is the effect of squeezing the airflow, increased as the buildings tend to get taller towards the city centre.

Question 27

The highest pressure is experienced in...

Answer 27

the upper part of the building.

Question 28

Building shape and spacing all affect...

Answer 28

the behaviour of the wind.

Question 29

Densely packed buildings allow...

Answer 29

air to move over the top, leaving the lower urban canopy layer relatively without turbulence.

Question 30

If no mixing by turbulence occurs...

Answer 30

then the pollutants at street level cannot be flushed away, causing smog situations.

Question 31

Large-scale convections

Answer 31

The heat island effect also produces large-scale convection and uplift over the whole urban area, leading to lowering the pressure. Air is drawn in from surrounding areas.

Question 32

The urban heat island is on average...

Answer 32

1-2 degrees warmer per year than surrounding area.

Question 33

The intensity of the urban heat island is...

Answer 33

the maximum difference between the temperature of the rural area and the peak urban temperature. Greater at night.

Question 34

High-pressure systems with clear nights and sunny days tend to...

Answer 34

increase the intensity.

Question 35

Heat islands are the result of:

Answer 35

- anthropogenic heat - height and the arrangement of buildings - the nature of the building materials - the presence of water - pollutants

Question 36

Height and arrangements of buildings

Answer 36

- tall buildings close together is the most important factor in generating urban heat island - more vertical surfaces so radiation tend to be reflected more - reduces the sky-view factor

Question 37

The sky-view factor is...

Answer 37

the amount of sky we can see without being impeded by a tall building.

Question 38

The sky-view factor tends to...

Answer 38

trap radiation, which reduces the chance of it escaping.

Question 39

In cities, there is a good chance of longwave radiation being...

Answer 39

intercepted by another surface and absorbed, reducing heat loss. The sky-view factor has a similar effect.

Question 40

Building height and arrangement is the key factor in creating urban heat islands as...

Answer 40

it is a way how the inputs and outputs of heat are controlled.

Question 41

Nature of building materials

Answer 41

- the specific heat capacity of materials effects how much heat can be stored - e.g. concentrate will warm up more rapidly and store more heat than wet mud

Question 42

Most of the surplus heat in urban areas is lost as...

Answer 42

sensible heat, heating up the atmosphere.

Question 43

Vegetation shades...

Answer 43

the soil so that stores less heat.

Question 44

The presence of water

Answer 44

- if there is little water at the surface, less surplus heat is lost as latent heat - cities have arrangements in the form of drains and sewers to remove surface water - twice as much heat is used in evaporation than used in sensible

Question 45

Presence of pollutants

Answer 45

-have both cooling and heating effect

Question 46

Sensible heat index gives...

Answer 46

the percentage of the total heat energy at the surface to raise the temperature of the air above. 85% in urban and 25% in rural.

Question 47

The presence of dust...

Answer 47

aerosols and gases can alter the amount of energy flowing in or out of the city.

Question 48

Smoky, dusty cities can reduce...

Answer 48

the amount of sunlight that reaches the city surface.

Question 49

Pollutant dome can absorb...

Answer 49

heat and prevent it from escaping. The build-up of ozone, CO2 and particulates help to absorb LW radiation and re-radiate it back.

Question 50

Clouds and precipitation

Answer 50

- urban areas have 5-10% greater cloud cover | - due to a greater concentration of hygroscopic nuclei (100x more than in rural areas)

Question 51

Precipitation is more common in...

Answer 51

cities 5-30% more.

Question 52

Fog is less common in...

Answer 52

cities due to higher temperatures and a higher concentration of hygroscopic nuclei, forming smaller droplets, which tend to discourage the formation of which fogs.