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Geography - Water Cycle > Unit 2 > Flashcards

Unit 2 Flashcards

1
Q

How does precipitation form?

A

in the atmosphere when water vapour condenses
- a small particle (dust or sea salt) = condensation nuclei
- colling of the air below the dew point = temp at which condensation occurs (dependent on humidity)

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2
Q

What happens to the temperature when the altitude increases?

A

decrease in temp

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3
Q

What is meant by lapse rate?

A

temp typically drops between 6.5 and 9.8 degrees for every 1000m increase in altitude

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4
Q

What happens if air rises or is uplifted in the atmosphere?

A

it will cool and subsequently reach dew point, causing condensation

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5
Q

What are the three main mechanisms for air uplift that produce rainfall?

A
  1. Orographic/relief rainfall
  2. Convection rainfall
  3. Frontal rainfall
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6
Q

How does orographic/relief rainfall occur?

A

occurs where there is a steep relief (mountainous areas)
- warm moist, less dense air is forced upwards
- reaches dew point and cools and condenses to form precipitation

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7
Q

How does frontal rainfall occur?

A

When warm tropical air collides with cool polar air
- when they meet the warm less dense air is displaced and forced upwards by the cold dense air
- the warm moist air reaches dew point and condenses

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7
Q

How does convectional rainfall occur?

A

when air is heated below, from land or sea
- causes air to rise, reach dew point and condense = cloud formation
- leads to short lived, intense rainfall

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8
Q

What are the two key theories of precipitation formation?

A
  1. Bergeron - Findeisen theory of ice crystal growth
  2. Collision Mechanism
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9
Q

What does the Bergeron - Findeisen theory suggest about ice crystal growth to form precipitation?

A

(occurs in clouds where temps are below 0, high altitude and latitude regions)
- pure water vapour droplets become supercooled and stay as a liquid below the normal freezing point of 0
- only freeze when in contact with a condensation nuclei
- forms ice crystals

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10
Q

What happens in the ice crystal growth theory when the snowflakes become too heavy?

A

too heavy to be kept aloft by updrafts and will begin to fall
- as they fall they pass through warmer air and melt to produce rain

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11
Q

How does the collision mechanism explain the formation of precipitation?

A

explains formation of rain in warm tropics where cloud temps are too warm for ice crystals to form
- ‘super sized’ condensation nuclei e.g. sea salt provide seeds around which very large droplets form
- the super droplets fall and collide with smaller droplets, absorbing them

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12
Q

What type of rainfall is the collision mechanism associated with?

A

convectional rainfall, heavy downpours and flash flooding
- infiltration - excess overland flow

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13
Q

What is meant by excess runoff?

A

when the rate at which the rain falls is greater than the rate at which if can infiltrate into the ground = excess runoff will occur

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14
Q

What are the physical factors that can cause excess runoff?

A
  • prolonged rainfall
  • intense storms
  • snowmelt
  • monsoon rains
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15
Q

What are the human factors that can cause excess runoff?

A

Deforestation
Urbanisation

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16
Q

What is the case study for prolonged rainfall?

A

Feb 2020 Floods UK

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17
Q

What was so significant in Feb 2020 for the U.K?

A

Wettest Feb and fifth wettest winter on record

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18
Q

Which three storms hit the UK in Feb 2020?

A

Ciara, Dennis and Jorge

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19
Q

What was the % anomaly (1981/2010) for feb 2020?

A

237% (difference relative to the average)

20
Q

What was the actual mm rainfall of the U.K in Winter 2019/20? (compared to feb 2020)

A

Winter = 469.7
Feb = 209.1 (almost half of all winter rainfall)

21
Q

What was the type of rainfall experienced in the UK during Feb 2020? (explain)

A

Frontal rainfall
meeting point between tropical and polar air = known as the polar front
position is controlled by the jet stream

22
Q

Which area was one of the worst affected during the Feb 2020 UK floods?

A

Flooding of the River Severn

23
Q

How many properties were flooded near the Severn Catchment during the Feb 2020 floods?

24
What is the case study for intense storms?
Boscastle Floods 16th August 2004
25
Intense storms produce high levels of precipitation and result in what?
flash flooding from infiltration-excess overland flow
26
How much infrastructure was damaged during the Boscastle floods?
5 buildings demolished and 60 more damaged
27
How many people where rescued and what was the death toll during the Boscastle floods?
over 100 people rescued 0 deaths
28
How did the intense storm that caused the Boscastle floods form?
was produced as a result from warm moist air from an ex category 2 hurricane, moving over the Atlantic ocean - air reached Cornwall over the 400m high Bodmin Moor (orographic rainfall) - Boscastle located at the centre of a convergence zone (frontal rainfall) - lead to intense precipitation
29
What was the peak rainfall during the Boscastle floods, over what period of time?
24.1mm recorded as falling in 15 mins
30
How much river levels rise in one hour during the peak of Boscastle floods?
2m every hour
31
What other two factors could have increased the levels of runoff during the Boscastle floods?
1. Geology and Topography 2. Land use
32
How did the geology and topography increase levels of runoff during the Boscastle floods?
- underlying geology of the catchment area is impermeable granite and slate - Boscastle sits in the bottom of a steep sided valley
33
How did the land use increase levels of runoff during the Boscastle floods?
- deforestation has occurred over much of the catchment which is now used for permanent grazing land - some urban development = increased impermeable surfaces
34
Why does snowmelt lead to excess runoff and flooding?
as it rains, it lubricates the snow above, which moves down the valley due to gravity However, there is no soil saturation, because the snow is preventing infiltration
35
What is the case study for snowmelt?
Red River Flooding of Fargo, 2009 (USA)
36
In March 2009, where did the Red River flood and what level did the river reach?
flooded in North Dakota and Minnesota USA, bringing record flood levels to Fargo at 12.45m (40.84 ft)
37
What were the conditions like in winter 2008/09 in Fargo?
high levels of snow and wide spread frozen ground followed by unusually high temps and resulted in rapid snow melt
38
How is runoff effected in an area of undisturbed forest?
1. high levels of evaporation and transpiration (rainfall) 2. rainfall is intercepted by leaves = drips to ground slowly 3. slow seepage from soil water and groundwater feeds the river 4. (there are high levels of saturated rock)
39
How is runoff effected in an area of disturbed/deforested area?
1. rainfall strikes soil directly, or grass near surface = soil compaction 2. rainwater does not infiltrate the soil, infiltration-excess overland flow 3. rainwater moves quickly over the surface of rivers causing flooding 4. (low levels of saturated rock)
40
In which area of forest (disturbed or undisturbed) does the moisture return to the atmosphere faster?
disturbed/ deforested = water on the surface, exposed directly to sunlight so evaporation will occur
41
In which area of forest (disturbed or undisturbed) does the shape of the hydrograph look more flashy?
disturbed/deforested = less processes such as infiltration and interception, water accumulates quickly resulting in more flash flooding
42
What is the case study for deforestation?
Haiti
43
What happened in 2008 in Haiti and how many where affected?
4 tropical storms hit, affected 800,000
44
What is the difference in % cover of Haiti rainforest between 1923 and present day?
1923 = 60% of Haiti covered Present day = 4% = significantly less infiltration and interception
45
How does urbanisation impact on runoff levels?
Often have surfaces, such as concrete and tarmac, which decreases rates of infiltration, throughflow and soil storage and increases surface runoff/overland flow
46
How does the lag time of a urban hydrograph differ to a rural hydrograph?
urban = the time between peak rainfall and peak discharge is much shorter
47
How does the steepness of rising and falling limb differ on an urban hydrograph compared to a rural hydrograph?
urban = increase in steepness

Geography - Water Cycle (4 decks)

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