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multidisciplinary group sponsored by the Chlorine Chemistry Council. Its mission is to promote science based practices and policies to enhance water quality and health by advising industry, health professionals, policy makers and the public.

Environmental Impact of El Niño: The Relationship Between Climate Variability, Water & Public Health

By Joan B. Rose, Ph.D.

El Niño (Spanish for "Christ Child") refers to a warming of the tropical Pacific Ocean with changes in wind velocity and atmospheric pressure. This climate variability dramatically affects the frequency and intensity of storms. The result can be droughts and increased flooding, both causing severe water management challenges.

The main feature of El Niño is a warm ocean current south along the coast of Ecuador, so named because it generally develops and peaks just after Christmas. This natural climate fluctuation, officially known as El Niño–Southern Oscillation (ENSO), occurs at irregular intervals ranging from two years to a decade. In the past 50 years, there have been 10 major El Niño events.

El Niño Explained

ENSO occurs in two phases. In an El Niño year, a high pressure system develops across the western Pacific while low pressure develops in the east. The easterly trade winds weaken and warm waters are pushed from west to east. The resulting pressure difference is known as the Southern Oscillation Index (SOI). During El Niño, the warm waters from the western tropical Pacific migrate eastward as the trade winds weaken.

This shifts the patterns of tropical rainstorms, further weakening the trade winds that reinforce changes in the sea surface temperatures. The ocean and atmospheric conditions in the tropical Pacific fluctuate in a cycle alternating between El Niño, the warm phase, and La Niña, the cold phase. La Niña can be characterized by a cooling of the tropical Pacific, a high pressure system across the eastern Pacific and low pressure in the west. In La Niña years, the easterly trade winds are restored and the warm water is pushed from east to west.

The Impact of El Niño

Current data show that the El Niño event taking place now is one of the strongest on record. It is second only to the 1982 – 83 event. Weak El Niños may raise sea temperatures only 1 to 2 degrees Fahrenheit. However, strong El Niño conditions, such as those experienced in 1982 – 83, may raise sea temperatures 15 to 20 degrees Fahrenheit. The dramatic effects of El Niño can be seen in marine and aquatic life, in agriculture and in the quality of our water supplies.



  • warmer sea temperatures

  • plankton and fish kills in coastal waters

  • lower sea levels

  • exposure of underwater, fragile coral reefs

  • higher sea levels

  • salt water intrusion into water supplies

  • coastal erosion and damage to shoreline and

  • flooding/increased rainfall

  • contamination of drinking water systems

  • flooding of wastewater systems

  • contamination of recreational sites and estuaries

  • waterborne illness

  • droughts

  • crop failure

  • increase in disease due to lack of water for
    sanitation and hygiene

  • blowing dust

  • pollution of viable water sources

  • decrease in near-shore coastal water quality

  • warmer, wetter, more humid weather

  • boom in mosquito population and subsequent
    increase in malaria and dengue fever

  • boom in termite population resulting in damage
    to buildings and homes



















    Conditions brought on by El Niño can lead to catastrophic effects: El Niño years often result in a shift toward early snowmelt, augmenting early spring flows and depleting late spring and summer flows in snowmelt dependent basins. This limited reservoir storage capacity creates a management challenge for water industry professionals to meet energy (hydropower) requirements, agricultural irrigation needs, and spring and summer flow targets. El Niño events also have adverse effects on freshwater fisheries, river and coastal water quality, wetlands, and municipal and industrial water supplies.

    Planning for the Future

    As communities develop disaster preparedness plans for severe weather, they also should prepare for the potential increase in diseases, such as waterborne illnesses, which may be influenced by a change in climate and in the quality and quantity of water resources.

    Further understanding of the impact of climate variability on the environment, public health and control of infectious diseases, as well as the conditions that lead to El Niño, is necessary to refine preparedness plans for public health protection. Sharing resources and knowledge requires interaction between climate research scientists, the water industry, and the public health community.

    The possibility of such a relationship may best be recognized through the environmental health sector, which could provide the following regular communication to the public health and scientific communities:

    1. Updates on El Niño predictions

    2. Better disease surveillance, communication with physicians, laboratories and environmental epidemiology programs

    3. Recording of localized weather events and proactive assessment of public health Impacts

    4. Review of preparedness plans

    5. Establishment of contacts within the wastewater and drinking water utilities

    6. Report on lessons learned from the 1997 – 98 El Niño.

    As the relationships between the ocean and atmosphere and associated global climate conditions are further understood, scientists will be able to accurately predict weather patterns, including the beginnings of El Niño episodes, up to one year in advance. As a result, the water industry and public health professionals can prepare for long-term human and environmental effects.

    Dr. Rose is a professor of microbiology in the Department of Marine Sciences at the University of South Florida, St. Petersburg, FL. She is an internationally recognized expert in the sources and transmission of waterborne diseases. Dr. Rose also serves as Vice Chair of the CCC Public Health Advisory Board.

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