El Niño and La Niña
Objectives
El Niño and La Niña (below) are excellent
examples of the complexity of our atmosphere and
its interrelatedness with the oceans of the world.
Overview of El Niño
El Niño is generally thought of as a phenomena that originates every few years off the west coast of
South America. In order to understand it, it is useful to review what normally happens in that area in
terms of winds and ocean temperatures.
Normal Situation
Off the coast of Peru, the prevailing winds are the SE Trades which help to blow warm water away
from the west coast of South America. This allows colder water from below to come to the surface. This
colder water contains nutrients which anchovies eat. Therefore, the anchovy industry has been
important to the Peruvian economy.
1982: A severe "El Niño" event devastated the Peruvian anchovy industry.
Why?
El Niño appears every few years often around Christmas time as evidenced by the unusual warming of
the surface waters near the west coast of South America. As a result of it frequently starting around
Christmas, the event has been given the name "El Niño" which means "The Little Boy" or "Christ
Child" in Spanish. The warming is due to a weakening of the prevailing winds so that warm water is
not blown away from the coast. Rather the water gets warmer and encompasses a larger area.
Consequently, the colder water and nutrients from below do not reach the surface.
A Key Understanding
Changes in wind patterns and ocean temperatures in one part of the planet can impact the entire
globe's weather.
eg 1982 El Niño:
- severe drought in India and Australia
- large storms struck California/Oregon=more landslides especially in California as lack of vegetation
- a milder and drier winter for British Columbia
Winter 1987 and 1998: The largest El Niño event of the 20th Century. Due to better monitoring of
ocean temperatures and the use of sophisticated computer models, scientists were able to predict El
Niño's arrival several months in advance helping people to prepare.
1998-1999 El Niño:
-More hurricanes along Pacific coast of Mexico (WEST SIDE)-damage to housing and flooding
Overview of La Niña
Every few years, the opposite of El Niño occurs - "La Niña" ("The Little Girl" in Spanish). In this
situation, rather than weakening, the trade winds strengthen, blowing more warm water away from
the west coast of South America. This allows an unusual amount of cold water to come to the surface.
The effects of La Niña are the opposite to those of El Niño so areas that become drier under El Niño
become wetter under La Niña. Generally though, the impacts of La Niña are less severe than those
under El Niño. In the winters of 1998/1999 and 1999/2000: La Niña events
- a wetter winter for BC with more snow in the mountains
El Nino and La Nina Effects on Canada
What are the effects of an El Nino on Canada? Off the coast of British Columbia, the warm coastal waters during an El Nino
tend to bring more southern marine species northward to our latitudes. With an El Nino, the returning Fraser River sockeye
salmon tends to favour travelling via the northern route through Johnstone Strait instead of the more commonly used southern
route through the Strait of Juan de Fuca. Since the sockeye in Johnstone Strait can only be caught by Canadian vessels, while the
ones in Juan de Fuca Strait can be caught by both American and Canadian vessels, an El Nino tends to shift the catch in favour
of the Canadians. The warmer the ocean along our coast, the warmer our winter temperatures. Mackerel from down south
made their way here and ate many salmon fry, which had an impact on the fish number 4 years later when they matured. We
had less water because of a lack snow, which also affected our ski industry. On a positive side heating costs were lower, nd snow
and ice were not factors in traffic accidents. Clearing snow was not a problem, so communities saved a lot of money.
During the winter of an El Nino event, the air temperature tends to be warm over most of Canada, with the greatest warming
centred around Manitoba-western Ontario, where a temperature anomaly of up to +3 degrees Celcius (averaged over the last
nine El Nino events) can be found. Southern Canada also tends to be drier during an El Nino winter. Southern British Columbia
tends to receive less snow.
In the case of the cold La Niña event-- the opposite of the warm El Niño event-- the coastal waters off British Columbia tend to
be cool. In a La Niña winter, the Canadian air temperature (especially west of Quebec) tends to be below normal, while the
precipitation in southern Canada tends to be above normal. Southern British Columbia tends to receive more snow. Poor
Canadian prairie wheat harvests often follow La Niña events.
In 1989:
 A series of storms approaching the Rocky Mountains from the west deposited heavy snow in southern British Columbia
and most of the prairies in January 1989. Heavy snowfall in the northern part of the region (over 400 cm in southern
British Columbia) resulted in numerous avalanches forcing closure of many highways north of Terrace. The Rogers Pass
was also made impassable by heavy snow on a number of occasions.
 The February 1989 cold snap proved beneficial to logging operations in British Columbia as it allowed the ground to
freeze permitting transportation of heavy machinery in order to haul timber from forested areas.
In 1995:
 In the 1995 La Niña, a late November storm dropped 70 mm of rain in just a few hours. Mud slides and flooding
resulted, and several streets were turned into fast-moving rivers. Heavy rains occurred again a few days later. As much
as 175 mm fell in some areas of the lower Mainland.
 The bitter cold of January 1996 was also felt on the west coast. In Vancouver a record for one-day consumption of
natural gas was set on the 9th. In the Fraser Valley the Trans-Canada Highway was closed after a 30 cm snowfall on the
20th; this was followed a few days later by another 15 to 20 cm. On Vancouver Island, where warmer conditions resulted
in the precipitation falling as rain, more than 50 landslides were recorded.
SUMMARY TABLE:
EFFECTS OF EL NINO
EFFECTS OF LA NINA