The El Nino weather cycle originating in the Pacific Ocean is intensifying drought from Africa to Asia. Why do El Nino and its sibling, La Nina, have such far-reaching climate impacts?On April 4, the President of Zimbabwe, Emmerson Mnangagwa, declared a "State of Drought Disaster" due to the "severe food situation caused by the El Nino effect."

Zambia and Malawi had already declared a disaster as El Nino-driven drought continued to devastate crops across southern Africa. This El Nino cycle, which scientists say began around June and peaked in December before starting to wane, is also behind extreme heat and drought in Southeast Asia — including in the Philippines, where schools have been forced to shut because of record temperatures. El Nino Weather Patterns May Affect India Adversely, Likely To Cause Monsoon Rain Deficit: Experts.

A Pacific Ocean weather phenomenon, El Nino — "the little boy" in Spanish — is linked to record global temperatures in 2023 that amounted to the hottest year on record. Its "little girl" sister, La Nina, creates global weather patterns that tend to be wetter and lead to intense storms and hurricanes.

How El Nino Causes Weather Extremes

The El Nino weather phase is part of the so-called El Nino-Southern Oscillation (ENSO), a climate pattern triggered in the Pacific Ocean. El Nino commonly occurs every two to seven years when regular trade winds moving east-west across the Pacific weaken and sometimes even reverse.

These winds usually blow across the equator and take warm water from South America towards Southeast Asia and Australia. But when the winds start to fail, the warmer water remains in South America and fails to travel west. As the warmth suppresses the usual upwelling of cold water in the eastern Pacific, extra heat in the atmosphere typically supercharges regional rainfall and causes flooding in northern South American countries like Bolivia.  El Nino: 2023 on Track to Be Hottest Year Ever on Record.

Meanwhile, the absence of warm water in the western Pacific can result in drought and extreme temperatures. Though predictions of a nightmare fire season in Australia in the summer of 2023-24 at the peak of the El Nino cycle did not come to pass, August-October 2023 were still the driest months for 120 years. Meanwhile, El Nino's disruption of ocean heat can alter the path of jet streams — strong winds far above the ground — that travel the planet guiding rains. This causes broad climate disruption, including the stalling of the monsoon in Indonesia and India, but also the reduction of hurricane activity in the Atlantic. La Nina Effect on Indian Monsoon: Monsoon 2024 Forecast Promises Early Arrival and Abundant Rainfall, Says IMD.

Furthermore, El Nino was partly to blame for heavy rains and flooding in East Africa in late 2023. By late last year, floods had killed 120 people and displaced 700,000 residents in Kenya.

While researchers have shown that direct impact of El Niño on east African rainfall is actually relatively modest, they add that it can kickstart a positive Indian Ocean Dipole, another weather phase that is bringing extreme flooding to the region.

La Nina Fuels Storms and Hurricanes

La Nina is another key phase in the ENSO, yet has an opposite impact since predominant east-west winds become stronger than usual. An increase of warmer water in the west brings increased rainfall to Australia and Southeast Asia. Meanwhile, La Nina phases can spark drought and wildfires in eastern Pacific regions from southwestern USA and Mexico through to South America.

La Nina also typically enhances hurricane activity in the Atlantic Basin, a phenomenon that is being exacerbated by record warm ocean surface temperatures in the Atlantic.

Impacts Are Hard to Predict

While La Nina and El Nino events are natural weather patterns, their relative impacts can vary depending on their timing, duration, and complex climate influences that include human-induced global heating. There is some evidence that climate change has made El Nino-Southern Oscillation events more frequent and intense.

Meanwhile, experts say that El Nino and La Nina cycles are likely to hit harder as the planet heats up. Hotter air, for example, holds more water and causes more extreme rainfall.

Researchers add that achieving net-zero greenhouse gas emissions through the phasing out of fossil fuels has the potential to limit both global heating, and ENSO impacts.

Sources

US National Environmental Education Foundation, "El Niño and La Niña: What’s the Difference?"

https://www.neefusa.org/story/climate-change/el-nino-and-la-nina-whats-difference

World Food Programme, "WFP urges global support as Malawi faces looming food crisis triggered by El Niño," April 2, 2024

https://www.wfp.org/news/wfp-urges-global-support-malawi-faces-looming-food-crisis-triggered-el-nino

Climate Council, "Spring Heatwave And Sweltering El Niño Summer Ahead Reignites Call For Net Zero Emissions By 2035," September 20, 2023

https://www.climatecouncil.org.au/resources/spring-heatwave-and-sweltering-el-nino-summer-ahead-reignites-call-net-zero-emissions-2035/