6.5

• ENSO cycle

  El Niño and La Niña
• ENSO cycle


  • Cyclic fluctuation of warm and cold sea surface temperatures and atmospheric pressure in central and eastern equatorial pacific
  • Causes extreme regional-scale weather and climate pattern changes
  • Considered the most powerful climatic force on Earth
• El Niño


  Prolonged unusual warming of sea surface temperature
• La Niña


  Caused by the strengthening of the easterly trade winds which blow more warm water toward the west and allows upwelling of cold water in the east
• ENSO term came into use only in the 1960's after regional variations in sea surface temperatures were observed to coincidence with atmospheric pressure variations between the eastern and western tropical pacific (Southern Oscillation)
• Normal conditions in the Pacific ocean


  1. Trade winds blow west along the equator, taking warm water from South America towards Asia

  2. Cold water rises from the depths to replace the warm water - a process called upwelling
• During an El Niño


  The easterly trade winds that push the water to the west become weaker and the accumulated warm waters tend to be drawn back to the east
• The warmer ocean


  Makes the easterly trade winds weaker and, as a consequences, the oceans become even warmer
• Effects of El Niño


  • Effects on Domestic water supply, irrigation, and electricity generation
  • Agricultural effects
  • Effects on marine ecosystem
  • Economic and societal effects
  • Other environmental effects
• El Niño and La Niña events occur every two to seven years, on average, but they don't occur on a regular schedule
• Generally, El Niño occurs more frequently than La Niña
• Health problems that arise during La Niña


  • Disease due to flood-contaminated
  • Leptospirosis
  • Dengue and malaria
  • Injuries and contusions
• ENSO Adapting Strategies


  1. Water Management

  2. Agricultural Sector

  3. Environmental conservation and geohazards

  4. Health Problems
• El Niño - constant rehydration, conserving household water supply and protect it from contamination, wear light clothing, avoid strenuous physical activity, listen to updates
• La Niña - boil and chlorinate water, properly wash and cleaning, avoid wading in floodwaters, dispose all possible breeding sites of mosquitoes
• Episodes of El Niño and La Niña typically last nine to 12 months, but can sometimes last for years
• The trade winds are weaker during an El Nino event
• Surface ocean temperatures of the eastern tropical pacific are colder than average during an El Nino event
• "El Niño" is a Spanish word means "Christ child" or "Jesus"
• La Nina occur twice as frequently as El Nino