Focus Areas E2- Oceanography

The general impacts of La Niña

Although many of us think of La Niña as just a weather event it can have major global impacts on the environment, on the economy and on individual human lives.

Typically, the global effects of a La Nina are less damaging than the stronger El Niño episodes. Nevertheless, during a significant La Niña episode, the impacts are felt by millions of people around the Pacific basin and beyond. At the same time that farmers in New South Wales may be welcoming in drought-breaking rains, over on the other side of the Pacific, in Peru, farmers may watch in despair as their crops whither away for lack of rain. In Bangladesh whole villages may be washed away in devastating floods at the very same time that residents in the Hollywood Hills of Los Angeles struggle valiantly to prevent their homes being consumed by ferocious bushfires. During the La Niña episode of 1998 / 99, for example, it was estimated that the lives of more than 450 million people on four continents were affected.

On the western side of the Pacific in places like the Philippines, the island of New Guinea and northern and eastern Australia, La Niñas are associated with heavy, extended periods of rain, with an increased likelihood of cyclones, and with a greater risk of extensive flooding. Sea levels can rise in coastal regions of New Guinea by almost half a metre and low-lying islands become swamped by deep ocean waves and by storm events energised by the warmer than normal surface waters of the western Pacific.

On the other side of the Pacific Ocean along the western coast of South America, during a La Niña, the temperature of the ocean drops as does the sea-level. Cold currents rise up along the coast. This results in enhanced growth of fish populations and other marine life as nutrients are brought to the surface by the upwelling cold currents. Sea bird populations increase and fishermen get better catches. On the mainland, countries like Ecuador and Peru experience lower than average rainfall with increased likelihood of drought while on the other side of the Andes mountain range, in countries like Brazil and Argentina,  La Niña episodes are associated with higher than average rainfall and greater risk of flooding.

In the Indian Ocean, La Niña episodes are commonly associated with floods in Bangladesh and other parts of South Asia.
In other words, the effects of La Niña are global. With floods, cyclones and hurricanes in nations on the western side of the Pacific, and with droughts and bushfire along the west coast of the Americas, farms and other productive land can be devastated causing food and produce shortages. This lack of primary production then has an effect on import and export costs which are passed down to the average consumer in countries that were not otherwise affected by La Niña. This produces economic effects around the globe.

Other impacts of a La Niña episode can include the loss of infrastructure, such as power and water, of possessions such as cars and boats, and of housing that must be re-built after flooding, cyclones, hurricanes and bushfires.  This then has an effect on both public and private insurance costs.  

Figure 1:  Storms, heavy seas and coastal flooding in the Central Coast of NSW, in June 2007
(Source: Shane Geerin, NSW, State Emergency Services).

Students learn about El Niño and La Niña
Students learn to identify features of El Niño and La Niña