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How the 2015-16 El Nino affected disease outbreaks

Topics Covered:

  1. Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.
  2. Disaster management.


How the 2015-16 El Nino affected disease outbreaks


What to study?

For Prelims and Mains: ENSO- El Nino and La Nia- causes, effects and impacts, global climate change and ENSO cycle.


Context: Global climatic disruptions due to the strong and extended positive phase of the ENSO conditions, or simply El Nino in 2015-16 increased the outbreak of diseases in the regions of its influence, according to a study published in the journal Nature.

The scientists analysed certain disease outbreaks in the 2015-16 period and tried to correlate them with higher temperatures and erratic rainfall patterns characteristic of the El Nino.


Key findings:

  • Major diseases like chikungunya, dengue, malaria, hantavirus, rift valley fever, cholera, plague and zika are affected by the weather events induced by El Nino.
  • They found that in regions like Southeast Asia, Tanzania, western United States and Brazil — which are generally affected by the El Nino — the spread of diseases came after shifts in rainfall, temperature and vegetation.
  • There was either excess of droughts or floods in this period which created the environmental conditions that favoured the growth and propagation of disease causing micro organisms and their carriers.
  • The study’s analysis indicates that the intensity of disease activity increased by 2.5-28 per cent during El Nino events than in other periods in the affected regions.
  • Similarly, excess land surface temperatures in Brazil and Southeast Asia aided the spread of dengue. El Nino, in itself, is a difficult phenomenon to track and study, which makes its consequences even more difficult to understand.


What is ENSO?

ENSO is nothing but El Nino Southern Oscillation. As the name suggests, it is an irregular periodic variation of wind and sea surface temperature that occurs over the tropical eastern Pacific Ocean. ENSO affects the tropics (the regions surrounding the equator) and the subtropics (the regions adjacent to or bordering the tropics). The warming phase of ENSO is called El Nino, while the cooling phase is known as La Nina.


What is El Nino?

El Nino is a climatic cycle characterised by high air pressure in the Western Pacific and low air pressure in the eastern. In normal conditions, strong trade winds travel from east to west across the tropical Pacific, pushing the warm surface waters towards the western Pacific. The surface temperature could witness an increase of 8 degrees Celsius in Asian waters. At the same time, cooler waters rise up towards the surface in the eastern Pacific on the coasts of Ecuador, Peru, and Chile. This process called upwelling aids in the development of a rich ecosystem.


What causes El Nino?

El Nino sets in when there is anomaly in the pattern. The westward-blowing trade winds weaken along the Equator and due to changes in air pressure, the surface water moves eastwards to the coast of northern South America. The central and eastern Pacific regions warm up for over six months and result in an El Nino condition. The temperature of the water could rise up to 10 degrees Fahrenheit above normal. Warmer surface waters increase precipitation and bring above-normal rainfall in South America, and droughts to Indonesia and Australia.


What are El Nino’s effects?

  • El Nino affects global weather. It favours eastern Pacific hurricanes and tropical storms. Record and unusual rainfall in Peru, Chile and Ecuador are linked to the climate pattern.
  • El Nino reduces upwelling of cold water, decreasing the uplift of nutrients from the bottom of the ocean. This affects marine life and sea birds. The fishing industry is also affected.
  • Drought caused by El Nino can be widespread, affecting southern Africa, India, Southeast Asia, Australia, and the Pacific Islands. Countries dependent on agriculture are affected.
  • Australia and Southeast Asia get hotter.
  • A recent WHO report on the health consequences of El Nino forecasts a rise in vector-borne diseases, including those spread by mosquitoes, in Central and South America. Cycles of malaria in India are also linked to El Nino.


Sources: down to earth.