Drought

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Drought

  1. 1. Drought
  2. 2. What is drought? <ul><li>A drought is an extended period of dry weather leading to extreme dryness. </li></ul><ul><li>This results in a shortfall of water supply which has hydrological and agricultural impacts. </li></ul><ul><li>Drought is different from most other hazards as it develops slowly as a creeping hazard. </li></ul><ul><li>Aridity and desertification are associated with drought but they are not the same. </li></ul><ul><li>Drought is characterised by moisture levels below normal for the area affected. </li></ul>
  3. 3. Types of drought <ul><li>We can define drought in three main ways: </li></ul><ul><li>· Meteorological drought: related to rainfall amounts </li></ul><ul><li>· Hydrological drought: determined by water levels in reservoirs </li></ul><ul><li>· Agricultural drought: related to the availability of water for crops  </li></ul>
  4. 4. The impacts <ul><li>Humans are conditioned to live with the average rainfall conditions therefore in times of drought we suffer. </li></ul><ul><li>Evapotranspiration, run off and infiltration will help determine the impact of the drought. </li></ul><ul><li>A drought may occur within a few weeks without rain in a humid area but will take longer to occur without rain in a arid area. </li></ul><ul><li>We might define drought in Libya as occurring when annual rainfall is less than 180 mm, but in Bali, drought might be considered to occur after a period of only 6 days without rain </li></ul>
  5. 5. Causes of drought <ul><li>The initial cause of drought is associated with a change in atmospheric conditions brought about by: </li></ul><ul><li>1. Persistent high pressure </li></ul><ul><li>2. El Nino and a change in ocean temperatures </li></ul><ul><li>3. Changing depression tracks </li></ul>
  6. 6. However droughts are very much exacerbated by
  7. 7. Characteristics of drought <ul><li>Not confined to a specific geographic location </li></ul><ul><li>Semi arid areas are most prone: Sahel, Great Plains USA, Australia. </li></ul><ul><li>Severity of droughts is intensifies by over cropping, overgrazing, deforestation </li></ul><ul><li>Mismanagement of arid lands is often related to economic development. This is often made worse by debt or dependence on cash crops for foreign income. </li></ul><ul><li>Also rapid population growth can have a direct impact upon the size of drought and the magnitude of this natural disaster. </li></ul>
  8. 8. Characteristics continued <ul><li>Each drought has its own unique characteristics and there is no scale of magnitude exists </li></ul><ul><li>On its own meteorological drought may not be a hazard if water supply systems can meet demand </li></ul><ul><li>Drought may result in secondary natural hazards such as dust storms, malnutrition related disease, locusts and wildfires </li></ul><ul><li>Severe agricultural drought can result in debt and famine </li></ul>
  9. 9. Drought in the Middle East 2007-now

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