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Geography - A - Global Systems > Block 4 - Precipitation + Excess Runoff In The Water Cycle > Flashcards

Block 4 - Precipitation + Excess Runoff In The Water Cycle Flashcards

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1
Q

What is a thermal?

A

Rising current of warm air

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2
Q

Outline the process of cloud formation?

A
  • Air uplifts (in one of three ways)
  • As air uplifts it expands
  • Air expansion decreases air pressure, so air molecules collide less + air temp falls
  • Water within the uplifted air condenses around CNNs when the air cools below its dew point or becomes water saturated
  • Water droplets grow, as more water vapour condenses onto the cNN or multiple droplets coalesce
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3
Q

What are CCNs?

A

Cloud Condensation Nuclei

Small particles, e.g. pollutants, around which water vapour condenses

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4
Q

Define condensation

A

State change from gaseous water vapour to liquid water

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5
Q

What must happen before precipitation occurs?

A

Clouds must form

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6
Q

What are the three types of air uplift?

A
  • Convectional
  • Frontal
  • Orographic
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7
Q

What happens in convectional air uplift?

A

Intense daytime heating of the land causes air adjacent to ground to be heated and rise

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8
Q

What happens in frontal air uplift?

A

Air masses of different temperatures (and densities) meet and the warmer, less dense air mass rises over the cooler denser air mass

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9
Q

What happens in orographic air uplift?

A

Air forced to rise over a barrier of higher land (e.g. mountain range)

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10
Q

What is rain shadow?

A

Dry area where little rain falls

Found after high land

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11
Q

How can humans intervene in the formation of clouds + rain?

A

Cloud seeding

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12
Q

Define cloud seeding

A

Aiming to change the type/amount of precipitation that falls in an area by dispersing substances that act as CCNs

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13
Q

Outline the process of cloud seeding

A
  • Planes/rockets release particles that act as CCNs

- This encourages more cloud formation + therefore more rain in this area

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14
Q

Define anti-cloud seeding

A

Particles released that act as the opposite of CCNs (prevent condensation, cloud formation + rainfall)

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15
Q

Give an example of humans changing the water cycle through cloud seeding

A

Beijing Olympics (2008)

  • Cloud seeding used to ensure good weather over Beijing
  • Cloud seeding North + South of city to draw away rain
  • Anti-cloud seeding over Beijing to prevent rain
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16
Q

Does precipitation occur from all clouds?

A

No

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17
Q

What are the two main theories of precipitation formation?

A
  • Bergeron-Findeison Process

- Collision Process

18
Q

Briefly summarise what the Bergeron-Findeison Process involves

A

Precipitation formation theory that involves ice crystal growth

19
Q

Briefly summarise what the Collision Process involves

A

Precipitation formation theory that involves condensation around ‘super sized’ CCNs that then collide + join together

20
Q

Outline the Bergeron-Findeison Process

A
  • Clouds (in high alt, below freezing conditions) contain mix of ice crystals + super cooled water droplets
  • Rapid flux movement of water droplets -> ice crystals
  • Ice crystals grow + are fractured into hexagonal snowflakes by fast air currents
  • Water continues to condense around large snowflakes
  • Eventually snowflakes become too large + dense so fall under gravity
  • As they fall, snowflakes pass through warmer air layers, become rain
21
Q

Outline the Collision Process

A
  • Large, ‘super sized’ CCNs provide ‘seeds’ around which water condenses into droplets
  • Water droplets formed are larger + heavier than normal droplets
  • Large droplets fall due to gravity
  • As they fall, these droplets overtake + absorb smaller droplets, as they have a larger terminal velocity
  • Heavy raindrops fall
22
Q

Where does the Bergeron-Findeison Process usually occur?

A
  • Cool, high altitude, high latitude areas

- UK in Winter

23
Q

Where does the Collision Process usually occur?

A
  • Warm, low altitude, low latitude areas

- UK in Summer

24
Q

What is excess runoff also known as?

A

Flooding

25
Q

What are the 4 main physical causes of flooding?

A
  • Prolonged precipitation
  • High intensity precipitation
  • Snowmelt
  • Monsoon rainfall
26
Q

What is prolonged precipitation and how is it a physical cause of flooding?

A

Precipitation that falls for a long time period

- Causes saturation-excess overland flow (soil saturated, no more water can infiltrate, causes excess runoff/flooding)

27
Q

What is high intensity precipitation and how is it a physical cause of flooding?

A

Precipitation that falls fast + heavy
- Causes infiltration-excess overland flow (intensity of rain so great, not all water can infiltrate, causes excess runoff/flooding)

28
Q

When do prolonged precipitation + high intensity precipitation usually occur?

A

During storms

29
Q

What is snowmelt and how is it a physical cause of flooding?

A

Accumulations of snow and ice suddenly melt

- Causes saturation-excess overland flow (soil saturated, no more water can infiltrate, excess runoff/flooding)

30
Q

What is monsoon rainfall and how is it a physical cause of flooding?

A

Season of high precipitation, driven by a reverse of the prevailing wind direction

  • Prolonged precipitation effects (saturation-excess overland flow)
  • High intensity precipitation effects (infiltration-excess overland flow)
31
Q

Where does monsoon rainfall occur?

A

Southeast Asia

32
Q

When is the monsoon season?

A

June -> Sept

33
Q

What are the 3 human causes of flooding?

A
  • Urbanisation (impermeable surfaces, drain/gutter/sewage networks, bridges)
  • River mismanagement
  • Deforestation
34
Q

What is urbanisation - impermeable surfaces - and how does it cause flooding?

A

Natural, permeable surfaces replaced with impermeable surfaces in urban areas (e.g. tarmac, concrete)
- Reduces infiltration, increasing surface runoff + chance of flooding

35
Q

What is urbanisation - network of drains, gutters, sewers - and how does it cause flooding?

A

Increase in drainage density through human networks

  • More water reaches river faster (lower lag time)
  • River is quickly overwhelmed, increasing surface runoff + chance of flooding
36
Q

What is urbanisation - bridges - and how does it cause flooding?

A

River channels are constricted when bridges are built

- River capacity reduced, bursting banks more quickly, increasing chance of flooding

37
Q

What is river mismanagement and how does it cause flooding?

A

Rivers managed poorly

  • E.g. Channelisation (river channel straightened) speeds up river flow, overwhelming downstream + increasing chance of surface runoff + flooding there
  • E.g. Deforestation (trees/plants removed) reduces interception, vegetation store + evapotranspiration, decreasing lag time + increasing surface runoff. Also less protected soil, more into river + this sedimentation reduces river capacity
38
Q

Do urban or non-urban areas have flashier hydrographs

A

Urban

39
Q

What are the three examples of physical causes of excess runoff?

A

Prolonged, high intensity precipitation (storms): UK 2007

Snowmelt: Kazakhstan 2018

Monsoon rainfall: Pakistan 2010

40
Q

What are the three examples of human causes of excess runoff?

A

Urbanisation: China 2020

River mismanagement: Romania 2006

Deforestation: Haiti 2004

Geography - A - Global Systems (8 decks)

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