What Causes Droughts

• Drought - when there is a lack of rain or less rain than normal over a long period of time

  • can lead to a deficit in the water supply with insufficient water to support plants, animals, and peopele
  • can occur anywhere but they are particularly common in Africa
• Most droughts occur when regular weather patterns are interrupted and evaporation exceeds precipitation
• Changes in atmospheric circulation patterns altering storm tracks and wind patterns (Reasons why droughts happen)

  • e.g. the patterns that prevent the northwards movement of the inter tropical convergence zone (ITCZ) into the Sahel region of Africa, which means that the moist rising air at the ICTZ does not move north to reach the Sahel
• Air in high pressure systems sinks and rain clouds generally do not form and if the sinking air covers a larger area, than normal or becomes prolonged, droughts can occur (Reasons why droughts happen)
• The El Niño Southern Oscillation is a weather event where the surface water in the Pacific Ocean along South America rises in temperature (Reasons why droughts happen)

  • these warmer waters alter storm patterns and can cause droughts in Australia
  • La Niña is the counterpart to El Niño - the surface water in the Pacific Ocean along South America decreases in temperature
  • cooler waters contribute to drier conditions in parts of North and South America
  • El Niño usually lasts less than a year and La Niña can last for 1-3 years
• Debate about the connection between drought and the current period of climate change (Reasons why droughts happen)

  • some scientists predict that warmer worldwide temperatures will mean decreased rainfall in some parts of the world leading to more drought events
• Agricultural practices can make land more vulnerable to drought (Reasons why droughts happen)

  • irrigation techniques have increased farmers’ dependence on water
  • overcultivation and overgrazing can lead to soil compaction and the soil is less able to hold water
  • as the soil becomes drier, it is vulnerable to erosion and eventually desertification
• Deforestation (Reasons why droughts happen) - lack of trees decrease soil infiltration and increases soil erosion
• Building a dam (Reasons why droughts happen) - building a dam on a large river can cause drought downstream of the dam by reducing the flow of water
• Inter Tropical Convergence Zone (ITCZ) - a low pressure belt that lies around the equator where the north-east and south-east trade winds meet

  • it recieves high precipitation because of intense heating from the sun
• El Niño Southern Oscillation (ENSO) - the change in the prevailing winds that leads to a change in the pattern of currents in the oceans of the south Pacific
• Natural weather patterns and human activities cause droughts