August 28, 2002

Weather-Related Disease Prediction

Scientists Use Weather Satellites to Curb Epidemics

Sea Surface Temperature Map

In April of this year, scientists at NASA's Goddard Space Flight Center and the Walter Reed Army Institute of Research announced that some diseases can be predicted from weather patterns. As a result of this prediction, resources can be allocated and distributed to treat the disease and to reduce or eliminate the source of the outbreak.

In areas that are usually dry, like East Africa, diseases carried by mosquitoes and rodents can often mushroom after a sudden flooding from heavy rainfall. In the dry American Southwest, outbreaks of Hanta virus, which is carried by deer mice and is sometimes fatal to humans, also are caused by sudden wet weather.

About twice a decade, mosquito-borne Rift Valley fever decimates the fetuses and young of livestock in East Africa. Humans can be infected too, but few die; the real casualty is the economy. Sometimes embargoes ban East African meat exports for a season or two.

Epidemiological studies have shown that outbreaks of Rift Valley fever follow sudden floods, and weather studies have shown that the flooding is triggered by El Niño and a similar climate disturbance called the Indian Ocean Dipole.

El Niño, a well-known weather phenomenon associated with heavy rains, occurs when a band of warmer-than-average water forms near the Pacific coast of South America, while Pacific waters near Australia and Indonesia become a bit cooler than usual (see image at top of page).

greening of East Africa The Indian Ocean Dipole is a similar type of temperature imbalance that can occur in the Indian Ocean, with the western part near Africa becoming warmer than the eastern part near Australia.

Tiny variations in these temperatures cause huge shifts in air circulation patterns — shifts that alter rainfall around the globe. When these two awesome events occur at the same time, East Africa is inundated.

With these new weather prediction models, as well as satellite monitoring that reveals the "greening" effect of heavy rains (see image at left), scientists can pinpoint, up to five months in advance, areas that may experience explosive growth of disease-carrying insects or rodents. Given warning, these areas can be treated to reduce insect or rodent populations and thus check the spread of disease. In addition, medical supplies and personnel can be directed to these areas before the disease reaches crisis proportions.

The bioclimatic rhythms of El Niño and the Indian Ocean Dipole may be here to stay, but science has found a way to help us deal with them.

For more information, see Rift Valley Fever.

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