Meteorlogical Causes Of Flooding Flashcards

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1
Q

What are the main causes of flooding?

A

Intense rainfall over a short period of time (flash flood)
Prolonged rainfall/ monsoons
Tropical storms
Snowmelt

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2
Q

What does most of the flooding seen in the uk relate to?

A

Mid-latitude depressions that brings 2 fronts

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3
Q

What 2 types of front does the uk experience?

A

Showers and rain occur with the passing of a warm front
Heavier rain falls with the cold front

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4
Q

What are isobars?

A

Lines joining points of equal pressure similar to contours which are shown on weather charts

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5
Q

How is pressure measured?

A

In Millibars

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6
Q

How many Millibars is an isobar?

A

4

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7
Q

What does a lower pressure mean on a weather chart?

A

A greater depression

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8
Q

How can depressions be recognised?

A

An area of closely spaced isobars often in a roughly circular shape where pressure is lower than the surrounding area

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9
Q

Where is the lowest pressure in a depression?

A

The middle

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10
Q

What is often associated with depressions?

A

Strong winds and heavy rain

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11
Q

What way are depressions blown in the northern hemisphere?

A

Anti-clockwise

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12
Q

How can a cold front be identified?

A

Bold lines with triangles

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13
Q

What does a cold front indicate?

A

A change in air mass where warmer air is being replaced by colder air

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14
Q

What are the characteristics of a cold front?

A

Often bring short spells of heavy rainfall in the form of showers and winds
Accompanied by a decrease in temperature
Veer in wind direction

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15
Q

How can warm front be identified?

A

Bold lines with semi-circles/ humps

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16
Q

What does a warm front indicate?

A

Cold air being replaced to a warmer air mass

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17
Q

What are the characteristics of a warm front?

A

Often bring prolonged sometimes heavy rainfall with strong winds

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18
Q

What happened in July 2007 in the UK?

A

A major flood event

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19
Q

What were the irregular weather conditions in 2007?

A

Jet stream followed an abnormal southern direction

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20
Q

What is the role of the jet stream?

A

Important for control factor for low pressure weather systems in the northern Atlantic

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21
Q

What did a change in the jet stream mean?

A

Usual anticyclonic/ high pressure weather system from Azores failed

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22
Q

What is the Azores?

A

Region of Portugal

23
Q

What happened in the uk due to the shift of the jet stream?

A

Resulting weather patterns produced exceptional rainfall throughout England and Wales

24
Q

What were the resultant conditions in the UK during 2007?

A

Mean temperatures across the UK were generally 1*c warmer
June precipitation was 136mm 190% average form 1961-1990 (wettest June on record)
Rainfall for may to July 2007 highest on record

25
Q

Why were the soils in 2007 highly saturated?

A

Early summer rainfall in 2007 meant that soils were already close to saturation and groundwater levels were higher than usual

26
Q

What are ground water levels like in a normal year in the UK?

A

Britains usually has lower ground water levels reducing the risk of flooding (acts as extra storage)

27
Q

When did some intense storms occur during summer 2007?

A

20th of July

28
Q

What did the intense storm on the 20th July result in?

A

A number of localised but severe flash floods

29
Q

What were some areas that experienced flash floods of 20th July 2007?

A

Stratford upon Avon
Leamington spa
Tewkesbury
Buckingham

30
Q

What were the economic effects of the 2007 summer flood?

A

Cost country £3.2bn
£2bn for homeowners and businesses

31
Q

What was the average repair cost of a flooded home in 2007?

A

£23,000- £30,000

32
Q

What was the problem for homeowners after the 2007 flood?

A

1/4 of homeowners were not fully covered by insurance

33
Q

What was the average cost per flooded business after the 2007 flood?

A

£75,000 - £112,000

34
Q

How much did the damage to communications and transport cost?

A

£230m

35
Q

What was the agricultural loss after the 2007 flood?

A

Loss of £50m
£1,150 per hectare

36
Q

What was the cost to the emergency services during/after the 2007 flood?

A

£27m

37
Q

What were the social impacts of the 2007 Uk flood?

A

Education- 400,000 pupil days lost due to school closures
Flooding of water treatment plant in Tewkesbury (worst post WW2 emergency) loss of piped water to 350,000 customers, 138,000 properties for over 2 weeks

38
Q

What were the demographic impacts of the 2007 UK flood?

A

13 people were killed
Rural households worse affected- stranded as minor roads not considered as important as major roads in towns and cities
Old and young most affected as they’re least mobile

39
Q

When did storm Desmond occur?

A

2015-16

40
Q

What were the meteorological causes of storm Desmond?

A

Unusually heavy rain and strong winds due to low pressure from the Atlantic

41
Q

How much rain did Honister in Cumbria get in 24 hours?

A

341.4mm

42
Q

How high did winds get in storm Desmond?

A

81mph

43
Q

How many categories are there for depressions?

A

5 categories

44
Q

What are the wind speeds for each depression category?

A

1- 74-95mph
2- 96-110mph
3- 111-129mph
4- 130-156mph
5- 157+mph

45
Q

How does a tropical depression form?

A

When low pressure is with thunderstorms that produce circular wind flow with maximum sustained wind flow below 39mph

46
Q

What is the typical maximum sustained wind speed for tropical depressions?

A

25-35mph

47
Q

When was the flood in Bangladesh?

A

1998

48
Q

What were some of the causes of flooding in Bangladesh?

A

Monsoon climate
Spring snowmelt
Deforestation in headwater area
River silt-up
Lying on a floodplain
Diversion for irrigation
Regularly hit by cyclones

49
Q

How did a monsoon climate cause flooding in Bangladesh?

A

Brings very heavy rain and snow
Soils are leached and heavy runoff results in soil erosion

50
Q

How does spring snowmelt cause flooding in Bangladesh?

A

Results in soil erosion and a rapid increase in river discharge

51
Q

How does deforestation in headwater area cause flooding in Bangladesh?

A

Trees are cleared for fuel and grazing land for growing population
Less evapotranspiration
More runoff
Faster soil erosion

52
Q

How does river silt up cause flooding in Bangladesh?

A

Raises river bed and reduces capacity of the channel

53
Q

What % of Bangladesh is built on a floodplain?

A

80% most of which is only 1m above sea level

54
Q

How does irrigation cause flooding in Bangladesh?

A

Removes som of the silt and prevent s the floodplain further downstream from being built up