El Nino and Hurricanes
ENSO and Infectious Disease
El Nino, Ocean Nutrients and Anchovy
Further Reading
The most severe El Niño of the century occurred in the winter of 1982 and 1983. Disastrous effects and meteorological changes occurred around the world. Total damages were estimated at over $8 billion.
Under normal conditions, the atmosphere of the Eastern South Pacific is dominated by an eastern center of high pressure. A zone of lower pressure prevails to the west and the resulting pressure difference causes the trade winds to blow east to west. The Southern Oscillation Index (SOI) is calculated by subtracting the sea-level pressure (SLP) in the west from that in the east. During an El Niño event, the SOI will have a negative value. When the SOI is negative, the trade winds may relax or sometimes even reverse. This is what happens during an El Niño. Since ocean currents are greatly influenced by the winds blowing above them, this ease of the trade winds also affects surface ocean currents, particularly the Peruvian Current.
The Peruvian Current is normally a cold current that moves northward along the coast of South America that causes an upwelling of cold, nutrient and oxygen-rich water that is conducive to dense concentrations of marine life. During an El Niño, however, the relaxation of the trade winds may allow warm water to appear at the surface of South America. This warm water not only kills off marine life, but also affects the atmosphere directly above it causing convection, which can cause intense rainfall in a region that is normally dry.
In addition to the ENSO effects along the coast of South America, there are many other global impacts. These climatic aberrations are called teleconnections because statistical correlations have been found between these atypical weather events and the ENSO. Among these teleconnections are droughts in Central America, Philippines, Southern India, Indonesia, Africa, and Australia. Large scale brush fires and forest fires- some on the order of millions of acres- are associated during these drought periods in Australia and Kalimantan (Borneo). Flooding is more prevalent in the United States, Cuba, Northern Peru, Southern Brazil, Northern Argentina, Eastern Paraguay, Bolivia, and Western Europe. These teleconnections statistically correlated with the ENSO have extensive social impacts that have been known to leave people homeless and poverty stricken, crops failed, and national economies disrupted.
Closer to home, the ENSO teleconnections found in the US are more clearly seen in the winter. Intense rainfall has been recorded in the Southern and Western US. Winters in the northern US may be unusually mild during El Niño years. Dense tropical rain clouds distort the jet stream like a rock in a river and results in warmer temperatures in New England. The prolonged and mild 1994-95 ENSO produced masive rains in California and a warm winter in the northern US and Canada.
In addition, the occurrence of U.S. landfalling hurricanes is reduced during El Nino years.
Dr. Gray's forecasting scheme is based on the following seven statistical factors:
Each of these factors are rated as plus (+), minus (-), or neutral (0).
Please see Dr. Gray's home page for more complete information straight from the source.
Consider India's autumn of disease last year. For much of the summer, temperatures had soared from their normal 80-90 degrees Fahrenheit and hovered around 124 degrees. Three-month monsoons led to conditions conducive to breeding malaria, dengue fever, and pneumonic plague. By the time the epidemics ran their course, the three diseases had afflicted thousands of people and killed as many as 4,000.
Climate variability has profound effects on the Earth's biota; and alterations in the incidence, duration, onset and intensity of storms, hurricanes, floods, and droughts greatly impact societies, productivity and development through changes in the diseases of human, animals, and plants. Because climate affects temperature, humidity, and precipitation, it influences human health via three interconnected pathways: 1) distribution and quality of surface water; 2) life cycle of disease vectors and host/vector relationships; and 3) ecosystem dynamics of predator/prey relationships which control populations of disease vectors. Changes in temperature, precipitation, humidity, and storm patterns, often related to the El Niño-Southern Oscillation (ENSO) phenomenon, are associated with upsurges of water-borne diseases such as hepatitis, shigella dysentery, typhoid, and cholera; of vector-borne pathogens such as malaria, dengue, yellow fever, encephalitis, schistosomiasis, plague and hantavirus; and of agricultural pests such as rodents, insects, fungi, bacterium, and viruses. And because climate variability can be forecasted, the potential exists to predict the likelihood of outbreaks of infectious disease.
ENSO Disrupts Ecosystem Dynamics
Climatic extremes effect animal, plant and human health by affording opportunistic species fresh terrain and generating new bursts of activity. Droughts encourage locusts and rodents, while floods foster fungi and mosquitoes. Fluctuations in climate which alter the structure or function of ecosystems can change the population dynamics of opportunistic pests and disease vectors, and of the predatory species which normally check their population growth. Owls, for example, help control rodent populations involved in Lyme disease and Hantaviruses. In the U.S., deforestation in the Pacific Northwest and prolonged drought in the Southwest, both encourage the proliferation of rodents by damaging owl refuges.
Rodents are involved in the life-cycle of many groups of diseases around the world. In the U.S. a new disease, the Hantavirus (with a 60% mortality rate), emerged in the "Four Corners" area near the borders of Colorado, Nevada, New Mexico, and Utah, following an explosion of the deer mouse population. Six-year droughts in the southwestern U.S. that devastated populations of owls, snakes, and other rodent predators, were followed by heavy rains in 1993 that increased food sources for rodents; in the absence predators the well nourished rodents flourished. The story is similar in southern Africa, where heavy rodent infestations closely followed the El Niño years of 1976, 1983, and 1993.
Since the 1960's researchers in southern Asia have observed an association between algal blooms and upsurges of cholera. It is becoming increasingly clear that ENSO warm events are also associated with upsurges of cholera, perhaps via the marine reservoir and/or the contamination of ground water accompanying ENSO-related flooding. Recent increases in coastal algal blooms and related cholera epidemics may be linked to climatic perturbations of ecosystems already stressed by pollution, habitat destruction, or the introduction of non-indigenous species.
ENSO Forecasting as a Weapon Against Infectious Disease
New developments in climate forecasting can provide the basis for a proactive approach to the spread of human diseases and agricultural pests--mitigating or preventing outbreaks before they occur, saving scarce public health resources and saving lives. Integrating health surveillance with environmental and climatological monitoring, disease early warning systems for conditions conducive to outbreaks can aid in the design of timely, ecologically sound and environmentally benign public health interventions. Climate forecasting can also be extremely useful in targeting scarce funding for surveillance and response, research and training, and emergency production of vaccines, drugs, and diagnostics, in the U.S. and abroad.
While climate forecasting cannot predict exactly where, when, and to what extent outbreaks will occur, current forecast capabilities combined with the state of understanding regarding the links between climate and health can be used in assessing the vulnerability of populations to outbreaks of infectious disease, and in determining the likelihood or risk of epidemics. Even at this early stage, probabilistic climate forecasting can arm public health practitioners with a powerful tool for reducing the morbidity and mortality caused by outbreaks of infectious disease. In this case, as in others, chance favors the prepared mind.
Climate Change and Human Health: An Assessment Prepared by a Task Group on Behalf of the World Health Organization, the World Meteorological Organization and the United Nations Environment Programme edited by A. J. McMichael, A. Haines, R. Slooff and S. Kovats
NOAA/PMEL/TAO El Nino Theme Page:
How
does El Nino-Southern Oscillation affect tropical cycllone activity
around the globe?
Problems
Arising from an El Nino
Current El Nino
Research January-March April-June Mr. Matt Sittel: "ENSO and US
Climate Variablity" Mr. Todd S. Richards: "ENSO and Florida
Precipitation" Dr. James J. O'Brien and Mr. Todd S. Richards: "ENSO
and Atlantic Hurricane Frequency"
The El Nino - How does
it work, and how does it affect the coast of British Columbia?
Note: Rainforests in Australia have also suffered from the unprecedented drought conditions of recent times. In 1991, the first recorded case of Australian rainforests dying in drought was reported by Dr Michael Olsen from the University of Queensland. The absence of effective rain for eight months severely dehydrated many vegetation species, many possibly beyond recovery. Normally fire-resistant species became vulnerable to fire, and weeds such as lantana took hold in the warm and dry conditions. Fruit-eating birds were reported to be declining while platypus communities starved as their habitats dried up. (Sydney Morning Herald, 19 November 1991).