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Environmental Risks and Hazards > L4 - Droughts > Flashcards

L4 - Droughts Flashcards

1
Q

Globally, what regions are most at risk of drought?

A
  • Sub-tropical high pressure zones

- Regions adjacent to cold currents e.g. East Pacific coastlines

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2
Q

Define a drought

A

“Drought is a condition of moisture deficit sufficient to have an adverse effect on vegetation, animals and man over sizeable areas”

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3
Q

How long to droughts tend to last?

A
  • Normal: Months-years

- Megadrought: Decades

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4
Q

What are the two main indexes of drought severity?

A
  • Standard Precipitation Index (SPI)

- Palmer Drought Index (PDSI)

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5
Q

What is the Standard Precipitation Index based on?

A

Probability of observed precipitation deficit occurring over a given prior time period

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6
Q

What is the Palmer Drought Index based on?

A

Soil Moisture, defined in terms of available moisture relative from norm

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7
Q

What would be the return period, SPI and PDSI of a minor drought?

A

3-4yrs

  • 0.5 to - 0.7
  • 1 to -1.9
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8
Q

What would be the return period, SPI and PDSI of a severe drought?

A

10-17yrs

  • 1.3 to -1.5
  • 3 to -3.9
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9
Q

What would be the return period, SPI and PDSI of an exceptional drought?

A

44yrs+
>-2
>-5

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10
Q

Name 4 categories s of drought (by severity)

A
  • Meteorological drought
  • Hydrological drought
  • Agricultural drought
  • Farming drought
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11
Q

What are some features of severe droughts?

A
  • Falls in ground-water levels
  • Increased risk of wildfires
  • Desertification
  • Soil erosion
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12
Q

What are some impacts of severe droughts?

A
  • Dust Bowl
  • Failure of agricultural systems
  • Aid needed
  • Strain on rural economy
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13
Q

List physical causes of drought

A
  • Sea surface temp. anomalies (SSDAs) e.g. El Nino/La Nina

- High rainfall variability e.g. Sahel

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14
Q

List human causes of drought

A
  • Poverty
  • War
  • Population strain on food supply
  • Environmental degradation
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15
Q

Characteristics of the SW US

A
  • Semi-Arid climate
  • Series of mountain ranges and desert basins due to rifting
  • Population growth esp. in Arizona
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16
Q

Why is SW US prone to drought?

A
  • In sub-tropical high-pressure zone
    • Causes descending air with lower relative humidity
  • Lower elevation -> increased temp
17
Q

What were the Impacts of the 1998-2004 Drought?

A
  • Wildfires (370,000 ha in 2002)
  • Pine mortality (>3 million acres)
  • $10 billion in 2002
18
Q

What droughts in the US tend to cost the most?

A

Those effecting the northern Great Plains (which have loads of agriculture)

19
Q

What were the two worst droughts in the 20th century in US

A
  • 1934 Dust Bowl Drought (‘29-‘40)
    - Approx. 65% of US severely or extremely dry
  • 1956 Southwest drought (‘46-‘56)
20
Q

What states were most effected by the Dust Bowl drought?

A

Kansas, Colorado, Oklahoma, Texas, New Mexico

21
Q

What caused the Dust Bowl?

A
  • Poor land management
  • Over-exploitation
  • Made worse by Great Depression
22
Q

When was the last US megadrought?

A
  • Series during Medieval Warm Period (900-1300AD)
23
Q

What is the primary source of evidence for historical megadroughts used by Cook et al. ?

A
  • Tree Rings
24
Q

What is thought to have caused the Medieval Megadroughts?

A
  • Persistent La Nina-like conditions in Pacific
    • Unusually cold in Eastern equatorial Pacific -> less evaporation
  • Due to warmer global climate?
25
Q

What are Pluvial Lakes? Where and when were they present?

A
  • Landlocked lakes as a present of glaciation

- Glacial period in SW US

26
Q

Name two mitigation methods

A
  • Disaster aid

- Insurence

27
Q

Name two protection measures

A
  • Environmental control (Irrigation, Boreholes)

- Hazard-resistant design (Dams, Pipelines, Reservoirs)

28
Q

Name three adaptation measures

A
  • Land-use planing (Water and soil conservation)
  • Community preparedness (Flexible agriculture)
  • Forecasting

Environmental Risks and Hazards (18 decks)

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