Brochures

La Niña: Canadian Perspective

• What is La Niña?
• How does this year's La Niña compare with other La Niñas?
• What are La Niña's global impacts?
• What has been the impact of previous La Niñas in Canada?
• Is there a link between climate change and La Niña?

Wind, water and temperature are part of an intricate set of connected elements that affect weather patterns around the globe. Weather events half-way around the world can affect local forecasts. Perhaps the most striking examples of weather phenomena affecting global climate are El Niño and La Niña.

Environment Canada scientists are tracking the 1998-99 La Niña. In Canada, La Niña can bring considerable fluctuations in weather patterns. However, most La Niña winters tend to be colder and snowier than normal.

Most of the prediction models are indicating that the easterly trade winds in the tropics would strengthen. This will intensify the up-welling of cold waters in the eastern Pacific. A moderate strength La Niña is possible during the winter of 1998-99, but considerable uncertainty remains about the timing and strength of the event. The response of the global atmospheric circulation and its effects on Canadian winter weather conditions is even more uncertain.

What is La Niña?

La Niña is an extensive cooling of the central and eastern Pacific Ocean. La Niña is also characterized by climate conditions that are sometimes opposite to those of El Niño (which brings warm ocean temperatures in the equatorial Pacific).

La Niña occurs when easterly trade winds in the tropics strengthen, intensifying the up-welling of cold waters off the coast of Peru and Ecuador. During La Niña, sea surface temperature can fall as much as 4 °C below normal.

The effects of La Niña are strongest during the Northern Hemisphere winter. While La Niña occurs less frequently than El Niño, weather patterns over North America associated with La Niña tend to be more variable.

During La Niñas snowfall is abundant from the interior of British Columbia to the Great Lakes region. In the United States, winters are warmer and drier than normal in the Southeast and cooler and wetter than normal in the Northwest.

How does this year's La Niña compare with other La Niñas?

In May, water temperatures in the eastern tropical Pacific showed a rapid transition from El Niño to La Niña like conditions. The water temperatures dropped by 8 °C to reach 2-3 °C below normal in a few weeks. Since mid June however, there has been little change. Recent satellite imagery from NASA indicates that warm waters from the 1997-98 El Niño continues to linger in parts of the eastern tropical Pacific and raises questions about the strength and timing of the emerging La Niña. Since 1976, there have been considerably fewer La Niñas compared to El Niños - the previous strong La Niña occurred 10 years ago (1988-89).

What are La Niña's global impacts?

The effects of La Niña are generally more direct and dramatic during the Northern Hemisphere winter. La Niñas may also affect weather patterns in other parts of the world, sometimes causing abnormally high rainfall in Southeast Asia and dry conditions in the desert areas of South America. Some impacts of previous La Niñas include the following:

• The Indian subcontinent received extremely heavy monsoon rains.
  
  
• Southeast Asia was lashed by torrential rains.
  
  
• Southeastern Africa experienced cool and wet winters.
  
  
• Eastern Australia received above normal rainfall.
  
  
• In the United States, northern states west of the Great Lakes experienced cold, snowy winters. The Southwest had high temperatures and low precipitation. There was an increased threat of hurricane activity in the mid-Atlantic states and winters in Alaska were unusually cold.

What has been the impact of previous La Niñas in Canada?

There have been 17 moderate-to-strong La Niñas since the 1900's. Each La Niña has its own unique characteristics, affecting Canada's weather patterns in different ways. These are some major weather events from the last two La Niñas in Canada.

La Niña 1995-96:

• Much of Canada suffered from a particularly long winter. Furthermore, from late October to March, many southern area locations had continuous snow cover.
  
  
• Winter temperatures were 11 °C below normal in Winnipeg - the second coldest winter on record. Temperatures did not climb above -20 °C for over a week and the overnight lows plummeted below -30 °C for 19 days in a row.
  
  
• The long-lived cold also affected Calgary. Residents were told to turn on their taps around the clock after weeks of cold weather caused pipes to freeze.

La Niña 1988-89:

• A drastic change occurred in the weather across the nation in February as an intense high pressure area over Alaska plunged southward causing record-breaking cold temperatures. Temperatures on the Prairies ranged from -30 °C to -40 °C.
  
  
• Cold Arctic air even reached the west coast of British Columbia, producing the longest cold spell of any February in Vancouver (January 31 to February 15) with minimum temperatures remaining below 0 °C. Fruit trees were damaged. Frigid air pushed as far south as Southern Texas and snow even blanketed Southern California.
  
  
• From mid-January, bitterly cold air poised over the Yukon intensified and produced record breaking low temperatures. At Old Crow, the temperatures remained below -40 °C for over a week.
  
  
• A build-up of bitterly cold air mass in the Northwest Arctic helped to produce the highest atmospheric pressure reading in North America. At Northway Alaska, the highest pressure reading of 107.5 kilopascals was recorded in February. A few days later, an all-time record high pressure reading was set in Saskatchewan and Manitoba.
  
  
• Central and Atlantic Canada also felt the frigid weather. Many localities in the Maritimes recorded the coldest February in over a decade.

Average winter conditions during past La Niñas

• The numbers indicate degrees Celsius by which the temperatures depart from normal.
• Environment Canada's official forecast for the 1998-99 winter can be viewed at http://weatheroffice.ec.gc.ca/saisons/index_e.html

Is there a link between climate change and La Niña?

Scientists are questioning whether climate change influences changes in climate associated with El Niño or La Niña. There is no consensus yet on any direct link. However, scientists are pursuing further research in order to provide confident answers to these questions.

Quick facts

• The phrase "La Niña" is Spanish for "the girl". Sometimes called "El Viejo"
  (old man), La Niña is characterized by unusually cold ocean temperatures in the equatorial Pacific.
  
  
• La Niñas appear approximately every 4-5 years and typically last 1-2 years.
  
  
• Global climate abnormalities of La Niña are less pronounced and in some areas tend to be the opposite of those associated with El Niño. However, the effects of La Niña are not always opposite to that of El Niño.After an El Niño, the climate does not always swing to a La Niña phase. There have been only 17 La Niñas compared to 25 El Niños since the turn of the century.
  
  
• La Niña is a natural phenomenon in the climate system that has been occurring for centuries. Detailed observations from ships led to reliable record keeping in the earlier half of this century.
  
  
• It is believed that La Niña's cooling of the equatorial Pacific tends to favour the development of tropical storms and hurricanes in the Atlantic. In contrast, El Niño conditions tend to suppress the development of hurricanes in the Atlantic, but increase the number of tropical storms over the eastern and central Pacific Ocean.

For Further Information

Amir Shabbar
Environment Canada
(416) 739-4435

La Niña Web site : http://www.tor.ec.gc.ca/lanina/

The Green Lane^TM,
Environment Canada's World Wide Web Site.