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…