Weather Effects of La Nina

It’s not good news for Georgia. While the peach state is supposed to get some rain this month, La Nina is expected to stay in force throughout the winter of 2008-09 and into the spring. Already in a state of drought, an intensifying La Nina means that little or no precipitation will fall on the southeast. While the Gulf Coast braced for Hurricane Ike, those farther inland hoped that at least some of the rainfall would reach them. Very little did. And now, that the hurricane season is almost over; there won’t be tropical storms to help out.

It all has to do with the trade winds that blow around the equator. In normal years, the Pacific is warm and the Atlantic is cold; that’s the way it’s supposed to be. In El Nino years, the winds from the west are stronger and shove warm water toward the east, destroying the fishing along the coast of Peru and beyond. In La Nina years, the winds blow from the east, pushing warm surface water west, leaving behind deep chilly water that rises to the surface. The effect is a “cold tongue” 3000 miles long from the Ecuador to Samoa. With all the extra warm water in the Pacific, heavier monsoons form over India, Australia, gets more rain, and even South Africa has increased precipitation. In the United States, more rain falls in the Northwest and less in the Midwest and South. The predictions for the Northwest this year though are fairly neutral neither La Nina nor El Nino.

La Nina (the girl child) is not as widely studied as El Nino (the Christ Child), but its effects have worldwide effects as well. There are four categories of El Nino intensity from strong to very weak but La Nina is simply La Nina. It is the positive phase of ENSO (El Nino Southern Oscillation) and is the reversal which ends El Nino. La Nina is not as well understood, but for those who live in areas affected by “the girl child,” the effects can be both negative and positive.

Peru is the site of many meteorological studies because it has been profoundly affected by both La Nina and El Nino. La Nina impacts the Southern Hemisphere in their winter (July-August) with lower than average temperatures. Rice doesn’t do as well, but cotton does better. Since fish thrive in cold nutrient-rich water, the fishing industry fares well in a La Nina year. In the 1996 La Nina, anchoveta and sardine catches increased and thus so did Peru’s exports of those products.

Fish may like the cold but humans don’t and in La Nina years, bronchial illnesses soar, especially in southern and central Peru with its high humidity. Since the area is already poor, increased illness adds to the suffering. There is also less rainfall along the coastal areas of Peru leading to drought conditions.

El Ninos usually show up every two to seven years and then are followed by La Ninas, harsh dry cold winters. In between there may be some normal years as it takes about four years to switch from La Nina back to El Nino. Because human lives and their ability to harvest and produce food are dependent upon the weather, it is important to be able to predict the full spectrum of the Southern Oscillation cycle. With increased concern about climate change, accurate measurement of cyclical events is extremely important. Thus, more technology is being directed at picking up the signs of La Nina. While we may never be able to control the weather, predicting it accurately can help humanity to be prepared.