Here comes La Niña

Wed, 05/17/2006 - 00:00
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Strong rains, flash floods, erosion, crop losses - these are just some of the problems Filipinos will encounter as La Niña hit the country this summer.

The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) based its forecast from the increases in the incidence of typhoons, floods and frequent heavy rains since November last year.

"The persistence of present oceanic and atmospheric patterns in the next two months will confirm the occurrence of a La Niña episode and continue to influence the climate of the Philippines," weather bureau chief Graciano Yumul said.

La Niña is the opposite of the phenomenon called El Niño, which was known originally recognized by fishermen off the coast of South America as the appearance of unusually warm water in the Pacific Ocean, occurring near the beginning of the year. El Niño means "the Little Boy" or "Christ Child" in Spanish. The name was used for the tendency of the phenomenon to arrive around Christmas.

La Niña, on the other hand, means "the Little Girl." It is sometimes called "El Viejo," "anti-El Niño," or simply "a cold event" or a cold episode.

El Niño and La Niña are opposite phases of the El Niño-Southern Oscillation (ENS0) cycle, with La Niña sometimes referred to as the cold phase of ENSO and El Niño as the warm phase of ENSO.

According to a primer prepared by the climatology and agrometeorology branch of PAGASA, ENSO occurs in the Pacific basin every two to nine years. It usually starts during the Northern winter (December to February) and exhibits phase-locking to annual cycles (El Niño and rainfall fluctuations associated with it tend to recur at the same time of the year). Once established, it lasts until the first half of the following year, although at times it stays longer (examples: 1939-1941, and 1989-1992 episodes). More importantly, El Niño events are often preceded and/or followed by La Niña.

Like El Niño, which reverses normal weather patterns, La Niña "tends to
accentuate the normal patterns," says Dr. Michael Coughlan, who is with the World Climate Program, which is part of the Geneva-based World
Meteorological Organization, the United Nations weather-monitoring agency set up in 1951.

In the tropics, global climate variations in La Niña tend to be opposite of
those of El Niño. "If you expect drought in the country with El Niño
because of reduced rainfall and less typhoons, there will be more than
normal rainfall and the normal but 'stronger typhoons' during a La Niña
episode that will cause floods and devastation of farms and property,"
explained Dr. Rafael D. Guerrero III, executive director of the
Laguna-based Philippine Council for Aquatic and Marine Research and
Development (PCAMRD).

Currently, scientists are still searching on possible mechanisms that could trigger the warming (El Niño) or cooling (La Niña) of sea surface
temperature in the equatorial Pacific. "Once the warming or cooling has
started or continued for a certain period of time," PAGASA said, "there are already existing climate models that could somehow predict its duration."

How does La Niña affect the country's weather? PAGASA has this answer:"Effects of La Niña could be manifested in above the normal rainfall conditions in major parts of the country, particularly along the eastern sections. This is mainly due to more intense northeast monsoon and tropical cyclone activities."

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