El Niño
Introduction
El Niño is a weather phenomenon which causes the sea surface temperature to rise in the
western tropical Pacific Ocean. It occurs every few years and is increasingly associated with
global changes to weather patterns. These changes can last many months and can cause drought
in some regions of the world, while others suffer extreme flooding as a consequence of El Niño.
El Niño means ‘The Little Boy’ or ‘Christ Child’ in Spanish and was named by fishermen off the
coast of South America in the 1600s when unusually warm water appeared in the Pacific Ocean.
The name was chosen because the warm water appeared near Christmas.
Two of the strongest El Niño events on record occurred in 1982-83 and in 1997-98.
What causes El Niño
Scientists don’t fully understand what initiates an El Niño cycle. Although different El Niño
cycles share similar characteristics, they do not always follow the same patterns from one cycle
to another. The Met Office in the UK has produced this video which helps to explain the causes
of El Niño and its consequences.
Characteristics of El Niño
Forecasters declare an official El Niño, when the following weather changes occur:
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The temperature in the upper 200 metres of the western tropical Pacific Ocean rises 0.5°C
above the long-term average and this warmer water moves eastwards along the equator
towards the western coast of South America. In the very strong El Niño year of 1997/98
there was a rise in sea temperature of more than 3°C. There is less upwelling of cold water
from below to cool the surface waters off the coast of South America.
∙
Tropical storms shift eastwards towards South America as the highest amounts of
evaporation take place above the warmest water in the east.
∙
Prevailing trade winds weaken in the central and western Pacific and may even reverse in
direction when under El Niño conditions.
During these conditions a feedback system between the atmosphere and the ocean is set up
which boosts El Niño conditions further.
What are the effects of El Niño?
El Niño can cause floods, droughts, forest fires and coral bleaching in different locations of the
world, although conditions and locations can vary in different El Niño episodes.
Americas
Africa
Asia-Pacific
Heavy rains in the southern
Horn of Africa and eastern
equatorial Africa
Wetter conditions in eastern
China and the Central Pacific
Drier and drought conditions
in the northern Horn of Africa,
southern Africa and some
areas in the Sahel
Higher than average
temperatures in Australia and
Southeast Asia
Significantly increased rainfall
in dry regions in Peru, Chile,
Ecuador and Mexico which can
cause barren deserts to
explode in flowers and can
cause severe flooding
Drier than average conditions
which can lead to drought in
north-eastern South America,
Central America and the
Caribbean
Higher than average rainfall
and snow as well as lower
temperatures in the south of
the United States of America,
from California right across to
the Atlantic coast
The northern regions of the
USA experience warmer
weather and less rainfall
Stalling and drying up the
monsoon in India causing drier
conditions
El Niño also has socio-economic and environmental consequences:
∙
Lower than average fish catches off the western South American coast as marine life moves
north or south to colder water where more nutrients such as plankton are able to thrive.
This has significant consequences for small-scale fishermen and large-scale fishing
industries.
∙
With less plankton available, the decline in fish stocks can lead to famine and dramatic
population declines for marine animals such as Galapagos penguins, marine iguanas, sea
lions and seals as well as sea birds.
∙
Flooding and erosion can destroy homes, schools, hospitals, roads and other infrastructure.
It can also cause severe transport delays and destroy crops causing food shortages and big
hikes in food prices.
∙
Droughts can threaten water supplies and can cause a large decline in food production,
particularly on land that depends on water for irrigation.
How often do El Niños occur?
On average, El Niño occurs every two to seven years but may arise more or less often. Each
episode tends to last 9-12 months. El Niño usually peaks between November and January,
though the build up to its full effects can be spotted months in advance and its effects can take
months to spread around the world.
Health risks associated with El Niño
El Niño conditions can exacerbate and trigger a range of health risks. Diseases thrive in
communities affected by increased rains, floods, storms and cyclones or increased dry
conditions and drought.
Health risks caused by heavy rain, floods &
storms
Health risks caused by drier conditions and
drought
Food insecurity which can make you more
vulnerable to disease
Malnutrition enhancing vulnerability to
infectious diseases
Increase in vectors (arthropods) and vectorborne diseases such as malaria, dengue fever,
chikungunya fever, African trypanosomiasis,
leishmaniasis, Chagas disease, yellow fever,
Japanese encephalitis and onchocerciasis
Infectious diseases which can be transmitted
from person to person. These include
diarrhoeal diseases.
Damaged or flooded sanitation infrastructure
can contaminate water leading to an increase
in water-borne diseases
Decreased water quality, lack of water supply
and sanitation leads to increased water-borne
diseases such as cholera
Damaged infrastructure causes disruption to
health services
Wildfires more likely which can damage
infrastructure and access to health facilities
Mental health and psychosocial effects
Decrease in air quality due to wildfires which
can lead to respiratory diseases
Direct injuries and fatalities
Heat waves can cause heat stress
What is La Niña?
Following the end of El Niño conditions, colder than normal waters can become established in
the tropical eastern Pacific and the trade winds blow more strongly than normal leading to a
weather pattern called La Niña. El Niño conditions happen more frequently than La Niña.
Collectively, El Niño and La Niña form part of an oscillation in the Pacific Ocean-atmosphere
system called the El Niño-Southern Oscillation, or ENSO cycle, which also has a neutral phase
when neither El Niño or La Niña prevail.
Advice for those working internationally and their families in areas affected by El
Niño
∙
Pay attention to personal health and hygiene. Wash your hands regularly or use an alcoholbased hand cleaner if water and soap are scarce.
∙
Ensure you have access to extra supplies of personal medication and a first aid kit as access
to health facilities may be severely curtailed.
∙
Follow specialist advice in any situations of risk or carry out your own risk assessment.
∙
Keep a battery powered radio, torch, water (enough to last one week) and non-perishable
food.
∙
Keep in regular contact with your employer, family and national embassy during El Niño
episode.
∙
Seek advice from InterHealth or another travel health adviser regarding medicine
treatment kits. You can contact our health centres in London and Nairobi for further
advice.
Sources
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What is El Niño?, Live Science, 20 August 2015, accessed 4 May 2017
∙
What are El Niño and La Niña?, US National Ocean Service, accessed 4 May 2017
∙
What is El Niño? The Guardian, 05 March 2015
∙
El Niño, Earth Observatory, 14 February 2017
∙
El Niño, National Geographic Society, accessed 4 May 2017
∙
El Niño and Health, Global Overview, World Health Organization, January 2016
InterHealth Worldwide Authors
Cathy Travis – Health Communications Manager
Rachel Walker – Travel Health Nurse Specialist
Last reviewed: May 2017
Copyright © InterHealth
While InterHealth endeavours to ensure that the information published in this guidance note is correct, InterHealth does
not warrant the accuracy and completeness of the material in this guidance note. The information in this guidance note
is for information only and should not be used for self-diagnosis or self-treatment. Readers are always encouraged to
seek medical help from a doctor or other competent professional health advisor