Droughts and High Pressure Systems

Droughts: Factors and Examples

  • Droughts occur in areas characterized by:
    • Little rainfall.
    • Shortage of water stored in rivers, lakes, and aquifers.
    • Human impacts like deforestation and intensive agriculture.
  • Examples:
    • Sub-Saharan Africa.
    • Developed areas like California and Australia.

High Pressure Belts and Low Rainfall

  • The Global Atmospheric Circulation Model creates high-pressure belts around 30° north and south of the Equator.
  • These belts lead to low rainfall, making these areas prone to droughts.

Heatwaves and High Pressure Systems

  • High-pressure systems are often linked to heatwaves.
  • These systems produce extended periods of clear skies, increasing temperatures and reducing rainfall.

Winter Effects of High Pressure Systems

  • Clear skies in winter can lead to freezing temperatures at night.
  • These temperatures can:
    • Affect transport routes.
    • Cause burst water pipes.
    • Create fog.

Summer Effects: Heatwaves, Droughts, and Wildfires

  • Heatwaves and droughts in summer can cause wildfires.
  • Wildfires are a common secondary effect of droughts and heatwaves, often having a greater impact than the drought itself.

Impacts of Wildfires

  • Loss of property, crops, resources, animals, and human lives.
  • Disruption of transportation.
  • Destruction of communications, power, and gas services.
  • Poor air quality from ash, leading to potential health problems.

Key Definitions

  • Aquifer: An underground layer of permeable rock containing water that can be extracted using a well/pump.
  • Global Atmospheric Circulation Model: Describes the movement of air around the planet powered by the hot equator.
  • Indian Ocean Dipole: Effect caused by changing temperatures of the Indian Ocean which affect evaporation rates. A positive dipole ‘turns off’ vital rain systems to Australia and causes droughts.
  • Snowpack: Layers of snow that accumulate in high altitudes. Their slow melting feeds streams and rivers.
  • Jet stream: Areas of high winds caused by the temperature differences in the atmosphere. Global warming reduces these temperature differences and so slows down the jet stream.

High Pressure Hazard Case Study

  • Important elements to include in a high-pressure hazard case study:
    • Name and date.
    • Location on a world map and description.
    • Specific figures like temperatures, duration, and compass directions.
    • Secondary effects, such as wildfires.
    • Impacts on the human and physical environment.
    • Short-term and long-term consequences on people.
    • Economic effects.

Global Drought Patterns and Global Warming

  • Global warming influences global drought patterns.
  • Changing ocean temperatures affect climate phenomena like the Indian Ocean Dipole, altering rainfall patterns and increasing drought risks (e.g., in Australia).
  • Rising land temperatures increase evaporation rates and reduce snowpack, lowering water stores in rivers and aquifers.

Jet Stream and Stalling Pressure Systems

  • Global warming is thought to affect the jet stream.
  • When the jet stream slows or stalls, pressure systems it moves from west to east also slow or stall, blocking other pressure systems.
  • A stalled high-pressure system can turn a normal one or two dry days into weeks, causing a drought.

Data

  • Drought events by administrative units.
  • Number of recorded events: 7 to 9, 5 to 6, 3 to 4, 1 to 2.
  • Data source: EM-DAT: The OFDA/CRED International Disaster Database, GIS analysis IRI, Columbia University, Cartography UNEP/GRID-Europe 2009.

Linking Impacts and Consequences

  • In exams, impacts and consequences should be linked together using connectives such as:
    • …this caused…
    • …as a result of…
    • …this meant…
    • …due to…
    • …consequently…
    • …therefore…
    • …so…
    • …because…