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Water Cycle > Unit 2 Notes > Flashcards

Unit 2 Notes Flashcards

1
Q

When does precipitation form?

A

When water vapour condenses, and requires a condensation nuclei, and cooling below the dew point.

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2
Q

What is the condensation nuclei?

A

A small particle around which condensation can take place.

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3
Q

What is the dew point?

A

The temperature at which condensation occurs, depends upon the humidity of the air.

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4
Q

What happens as altitude increases?

A

Temperature decreases.

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5
Q

What is the lapse rate?

A

The change in temperature with altitude.

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6
Q

How does the lapse rate change temperature?

A

Temperature drops between 6.5-9.8 degrees for every 1000m increase in altitude.

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7
Q

What are the main mechanisms of air uplift producing rainfall?

A

Orographic rainfall, relief rainfall, frontal rainfall.

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8
Q

What happens if there is a positive correlation between topography and rainfall?

A

There will be more rainfall under a higher altitude.

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9
Q

How is orographic rainfall formed?

A

Air blows up into an area of high altitude, forced upwards. Air cools, reaches dew point, condensation occurs. Water vapour changes into a liquid.

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10
Q

Where is orographic rainfall found?

A

Upland western regions of the UK, Westerly winds from the Atlantic Ocean. Rise over areas like Dartmoor, Snowdonia, Lake district.

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11
Q

What are the first two steps of convectional rainfall forming?

A

Energy of the sun heats the earth’s surface, causes water to evaporate, changes to water vapour, Warm, moist air rises, boils, reaches dew point, results in condensation.

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12
Q

What are the final two steps of convectional rainfall forming?

A

Leads to development of cumulonimbus clouds, as clouds continue to grow. Weight of water droplets leads to precipitation.

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13
Q

Where is convectional rainfall found?

A

Tropical rainforests, Tropical climates. South east of the UK in Summer.

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14
Q

What are the first two steps of frontal rainfall forming?

A

Two air masses of different temperature and density meet, but don’t mix. A front is the boundary separating two different air masses.

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15
Q

What are the final two steps of frontal rainfall forming?

A

As cold air is denser than warm air, warm air is forced upwards. As it rises, cools and reaches dew point, resulting in condensation and water vapour.

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16
Q

Where is frontal rainfall found?

A

The UK, where warm tropical air collides with warm polar air.

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17
Q

What are the two main mechanisms of precipitation?

A

Bergeron - Findeisen theory of ice-crystal growth, Collision mechanism.

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18
Q

What are the first two steps of the Bergeron - Findeisen theory?

A

Occurs in clouds where temperatures are just below 0 degrees, higher latitudes, and higher altitudes. Water vapour droplets can become supercooled, stay as a liquid below the normal point of freezing.

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19
Q

What are the next two steps of the Bergeron - Findeisen theory?

A

Dust particles act as condensation nuclei, and allow droplets to freeze. Upon contact with other supercooled droplets, they will also freeze, enables snowflakes to form.

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20
Q

What is the final step of the Bergeron - Findeisen theory?

A

Eventually, large snowflake becomes too heavy to be kept aloft.

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21
Q

Where does the Bergeron - Findeisen theory operate?

A

Over the UK, where cloud temperatures are below 5 degrees, and temperatures close to the ground remain below 2 degrees, snow reaches the ground.

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22
Q

What are the first two steps of the collision mechanism?

A

Explains the formation of rain in tropics where cloud temperatures are too high for ice crystals to form. Super sized condensation nuclei around which very large water droplets form.

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23
Q

What are the final two steps of the collision mechanism?

A

Larger super droplets fall and collide with smaller droplets. Associated with conventional rainfall resulting in heavy downfall pours and flash flooding, because of infiltration - excess overland flow.

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24
Q

What is excess runoff?

A

The rate at which the rain falls is greater than the rate at which it can infiltrate into the ground.

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25
Q

What are the natural factors affecting excess runoff?

A

Prolonged rainfall, intense storms, snowmelt, monsoon rain.

26
Q

What are the human factors affecting excess runoff?

A

Deforestation, urbanisation.

27
Q

What happened in the UK in February 2020?

A

Prolonged rainfall.

28
Q

How much rainfall did the UK experience in the whole winter, compared to February?

A

496.7mm - Whole winter. Half of the rainfall in winter was in February.

29
Q

What is the average winter rainfall since 1981?

A

143mm.

30
Q

Which areas were the most affected?

A

The North of England and Wales.

31
Q

Which areas were the least affected?

A

Scotland, South East England.

32
Q

What was the main type of rainfall experienced during this time?

A

Frontal rainfall - The polar front stayed over the UK for most of the winter in 2020.

33
Q

What is the characteristic of the River Teme?

A

Flashy, as it has a steep rising limb, and falling limb.

34
Q

What happened to the river level?

A

It rose from 1.6mm to 6mm, in just over 1 day, a short lag time.

35
Q

What were the impacts of the Boscastle floods?

A

5 buildings demolished, 60 damaged. 30 vehicles washed into harbour, 100 people rescued.

36
Q

How were the Boscastle floods produced?

A

As a result of warm moist air from an ex-category 2 hurricane, which moved eastward over the Atlantic ocean.

37
Q

What happened to air after it came from the atlantic ocean?

A

It rose over Bodmin moor, condensed to form orographic rainfall.

38
Q

Where is Boscstle located?

A

In the middle of a convergence zone, as two air masses moving in opposite directions converged, forming frontal rainfall, leading to intense precipitation.

39
Q

How much rain fell in two hours in Boscastle?

A

75mm of rain - the same amount as the whole month of August. 24.1 mm of rain was recorded in 15 minutes at the peak.

40
Q

What did this lead to?

A

2m rise in river levels in one hour, resulting in flooding.

41
Q

How did Geology affect runoff?

A

Underlying geology of catchment area is impermeable granite and slate. Boscastle is in the bottom of a steep sided valley.

42
Q

How did Land Use affect runoff?

A

Deforestation has occurred, and much of the catchment is now used for permanent grazing land. Urban development.

43
Q

How was Boscastle a factor of intense rainfall?

A

75mm of rain in two hours. 24mm of rain in 15 minutes. 2m river level rise. Air from atlantic ocean.

44
Q

How was Boscastle not affected by Intense rainfall?

A

Deforestation caused less interception. Rock is impermeable, meaning there is less infiltration at ground level. Boscastle is low lying within a valley, meaning rainfall would travel down.

45
Q

What are the key facts of the Red river flooding of Fargo?

A

March 2009 - Red river flooded in North Dakota and Minnesota. Brand record levels to Fargo at 12.45 million. Winter of 2008/09 saw high levels of snowfall, and frozen ground. Brought unusually high temperatures, resulting in rapid snow melt.

46
Q

Which human factors cause excess runoff?

A

Deforestation, Urbanisation.

47
Q

How did deforestation cause excess runoff?

A

Much of the forest which covered land in England, Wales, and Scotland has been removed. Leads to higher flood risk.

48
Q

What are the effects of Undisturbed forest?

A

Higher evaporation, lower rainfall, water drips to ground slowly.

49
Q

What are the effects of a degraded forest slope?

A

Rainfall strikes soil directly, causes soil compaction. Rainwater doesn’t soak into the ground, stays at the surface causing runoff. Rainwater moves quickly over the surface.

50
Q

How does deforestation affect quantity of precipitation reaching the surface?

A

Forested - Lower. There are higher rates of interception loss. Deforested - Higher. There is less interception, more water reaches the ground.

51
Q

How does deforestation affect the amount of infiltration?

A

Forested - Lower - Tree roots increase micropore spaces. Deforested - Higher - Soil is more compacted, reduction in pore spaces.

52
Q

How does deforestation affect the level of the water table?

A

Forested - Increased infiltration, increased percolation - Lower. Deforested - Higher - Reduced infiltration, increased percolation.

53
Q

How does deforestation affect the return of moisture to the atmosphere?

A

Forested - Higher - Increase in plant uptake, increased levels of evapotranspiration. Deforested - Lower - Reduced vegetation cover, lower evapotranspiration.

54
Q

How does deforestation affect the shape of the hydrograph?

A

Forested - Less flashy - Increased throughflow, baseflow, and lag time. Deforested - More flashy - Would be a higher amount of surface runoff into a river, therefore increasing the volume. Decreased lag time.

55
Q

What does a huge increase of deforestation lead to?

A

More surface runoff, as there is more compacted soil. This causes the soil to become infertile.

56
Q

What % of Haiti was covered by forest in 1923?

A

60%.

57
Q

What do trees protect from, and what does this lead to?

A

Protect from the impact of tropical storms, prevent soil erosion, regulate the water cycle. Has led to topsoil being easily removed by rain running down the mountainside, deposited in rivers, lakes and bays.

58
Q

What were the impacts of deforestation in Haiti?

A

800,000 people were affected, 793 people died, 548 people were injured, during hurricane season.

59
Q

What does urbanisation mean for surfaces?

A

Makes some surfaces impermeable, and concrete and tarmac increase surface runoff and overland flow, decreasing rates of infiltration, throughflow and soil storage.

60
Q

What happens to runoff in rural locations?

A

Natural ground cover have higher rates of infiltration, lower rates of runoff.

61
Q

What happens to runoff in medium density locations?

A

Lower rates of infiltration, higher runoff.

62
Q

What happens to runoff in high density residential areas?

A

Lowest rates of evapotranspiration, highest rates of runoff, lowest rates of infiltration.

Water Cycle (6 decks)

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