(The Warm Phase)
is a large scale oceanographic / meteorological
phenomenon that develops in the Pacific Ocean, which is associated with
extreme climatic variability; i.e., devastating rains, winds, drought, etc.
It is the migration, from time to time, of warm surface waters from the
western equatorial Pacific Basin to the eastern equatorial Pacific region,
along the coasts of Peru and Ecuador. This condition can prevail for
more than a year, adversely affecting economies in both local and global
El Niņo translates from Spanish as the "Boy Child" or the
"Little One". It used to be considered a local event along the coasts
Peru and Ecuador. The term was traditionally used by the Peruvian
anchovy fishermen to describe the appearance of a warm ocean current
flowing along the south American coast around Christmas time.
Under normal conditions, the prevailing southeasterly trade winds
produce a surface current flowing toward the equator along the western
South American coast. The waters leaving the coast are replace by
colder waters from below (upwelling), which is rich in phytoplankton,
the food source of anchovy.
The warm current (El Niņo) temporarily displaces nutrient-rich
upwelling cold water resulting in the heavy harvest of anchovies. The
abundant catch, however, is shortlived. What follows is a sharp decline in
the fish population , resulting in a lesser catch. At times, warming is
exceptionally strong and ruins the anchovy harvest.
Characteristics of El Niņo
- It occurs in the Pacific basin every 2 to 9 years;
- It usually starts during the Northern winter (December to February);
- Once established, it lasts until the first half of the following year,
although at times, it stays longer;
- It exhibits phase-locking in annual cycles (El Niņo and rainfall
- fluctuations associated with it tend to recur at the same time of the
- It usually has a biennial cycle (El Niņo events will often be preceded
Climatic Indicators of El Niņo in the Philippines
and/or followed by La Niņa).
Abnormalities such as:Effects of El Niņo in the Philippines
- delayed onset of the rainy season
- early termination of the rainy season
- weak monsoon activity
*isolated heavy downpours with short duration
- weak tropical cyclone activity
*far tropical cyclone track
*less no. of tropical cyclones entering the PAR
*less intense tropical cyclones
In the Philippines, drought events are associated with the occurrence
of El Niņo episodes. Second and third order impacts of El Niņo related drought events
in the Philippines include:
(a) environmental (degradation of soil which
could lead to desert-like conditions if persistent, effect on water quality like
salt water intrusion, high forest/grass/bus fire risk, domestic water supply
(b) social (disruption of normal human activities, migration to
urban communities, human and health problems, etc.); and
(c) economic (unemployment,
food shortages, significant reduction in the productivity and subsequent revenue
of various industries, hydro-electric power generation, etc.).
(The Cold Phase)
La Niņa develops over the central and eastern equatorial
Pacific and is characterized by unusually cold surface temperatures
of the ocean. La Niņa is associated with extreme climatic
variability such as devastating rains, winds, drought, etc.
This condition can prevail for two to three seasons (six to
nine months) thus affecting the economy on both the local and
global scales. The term La Niņa (the Little Girl) was
used by many scientists and meteorologists to differentiate
it from El Niņo. It is sometimes called El Viejo (Old Man),
Anti-El Niņo, or simply "cold event" or "cold episode".
Southern Oscillation/Walker Circulation
La Niņa events are also linked to a change in atmospheric
pressure known as the Southern Oscillation (SO). This is
characterized by a seesaw (positive) in the atmospheric pressure
between the western and central regions of the tropical Pacific
Ocean, with one center of action located in the vicinity of
Indonesia and the other center located over the central Pacific
Ocean. The index that measures the magnitude of the SO is
known as the Southern Oscillation Index (SOI) and it is
obtained by calculating the difference in atmospheric surface
pressure between Tahiti and Darwin, Australia. The Southern
Oscillation results from pressure variations which cause
changes in the wind circulation, also known as the Walker
circulation. In normal conditions, the prevailing
wind comes from the southeast to east. During La Niņa, stronger
than normal easterly winds occur throughout much of tropical
Pacific. These stronger winds push greater amounts of warm
surface waters far into the western tropical Pacific. Below
normal sea surface temperatures (SSTs) over eastern tropical
Pacific and simultaneously above normal or positive anomaly SOI
indicate a global-scale climate variation defined as the La Niņa
Is La Niņa a New Phenomenon?
La Niņa is not a new phenomenon. Evidence suggest that La
Niņa events have existed for thousands of years in the past.
However, it is only in the last decade that a satisfactory
understanding of how they form and are maintained has been gained.
Some of the La Niņa events on record are 1955-56, 1964-65, 1970-71,
1973-74, 1975-76, 1988-1989 and 1995-1996.
How Are La Niņa Events Detected?
La Niņa events in the tropical Pacific Ocean can now be
detected by many methods, including satellites, moored buoys,
drifting buoys, sea level analysis and expendable bathythermographs.
This research observing system is now evolving
into an operational climate observing system. Large computer
models of the global ocean and atmosphere use data from this
observing system as input to predict/monitor La Niņa, as well
as El Niņo. Other global models are used for research to further
understand the phenomenon.
Are All La Niņa Events The Same?
La Niņa events share many general characteristics although
every one is somewhat different in magnitude, duration and
resulting global climatic impacts. Magnitude can be determined
in different ways, such as variations in the Southern Oscillation
Index (SOI). Another measure of the magnitude is the sea
surface temperature anomaly (difference between the observed
and average values) which could either be positive (hotter
than normal) or negative (cooler than normal) over specific
region of the Pacific ocean, particularly in central and eastern
How Does La Niņa Affect Our Climate?
Impacts of La Niņa on Philippine climate include anomalies
in rainfall, temperature and tropical cyclone activities.
During La Niņa conditions, major parts of the country
experience near normal to above normal rainfall conditions
particularly over the eastern sections of the country.
La Niņa conditions also favor tropical
cyclone formation over the western Pacific which tend to
increase the number of tropical cyclones.