El Niño’s Impact is Global — and Often Catastrophic

El Niño is a naturally occurring weather pattern that causes warmer ocean waters around the equator. When the ocean waters in the Pacific Ocean get warmer, the easterly winds—which blow from east to west—can be disrupted or even blow in the opposite direction (westerly winds). This change in water temperature and wind patterns causes severe and unusual weather disruptions throughout the world. El Niño (Spanish for "the Christ Child") happens irregularly, every two to seven years, and lasts for nine to 12 months.

No two instances of El Niño are alike. The exact nature of the weather disruptions caused by El Niño cannot be accurately predicted until the event begins. However, agencies like the National Oceanic and Atmospheric Administration (NOAA) and the United States Geological Survey (USGS) have been tracking El Niño weather patterns for years to help us better understand this unique scientific phenomenon. Let's look at different changes to the weather that occur when El Niño blows in.

For information on El Niño and the weather patterns associated with its occurrence, we sourced reliable weather science sources such as NOAA and USGS. We also looked at reliable news sources such as CNN to find evidence of severe or unusual weather events that occurred during El Niño years. We corroborated with additional peer-reviewed studies by climate and weather scientists to help us ensure that the events we reported on were, indeed, related to El Niño rather than simple strange occurrences. This research helped us gain a better understanding of the overall impacts of El Niño on the global climate and weather patterns.

One of the most prominent effects of El Niño is changes to the global patterns of precipitation. Many people associate El Niño events with heavy rainfall, landslides, and flooding. California experienced severe weather disasters related to the heavier-than-average rainfall that accompanied El Niño in the 1980s and 1990s, leading many people to assume that El Niño was primarily causing heavier rain patterns. Indeed, heavier-than-average precipitation occurred in over 80% of documented El Niño events according to NOAA. However, while the occurrence of El Niño does bring overall changes to the global patterns of precipitation, heavier-than-average precipitation isn't a universal effect of El Niño. These conditions are typically centralized in the Gulf of Mexico, Southern Texas, and Southern Florida. Outside of these areas, we do see changes to precipitation patterns, but they usually aren't heavier-than-average, instead, other areas may see lighter-than-average rainfall.

Where the rainfall increases and by how much correlates to the strength of the overall El Niño event. If the warming of the ocean is stronger, there is more rainfall and the area of effect is greater. However, in weaker or moderate events, the correlation between increased precipitation and El Niño is weaker. During weaker event years, there may not be significantly noticeable effects on the rainfall during El Niño, especially as we move into the Southwest and away from the Gulf of Mexico. Some events even caused a marked reduction in rainfall outside of the Gulf of Mexico. Thus, while El Niño can be a predictor of increased precipitation in some areas, this effect shouldn't be considered universal for the event.

The Pacific Jet Stream is a fast-moving narrow current of air that flows from west to east over the Pacific Ocean. It exists high up in the atmosphere and connects the El Niño Southern Oscillation (ENSO) to the North American winter climate. There are many jets in Earth's atmosphere, but it is the Pacific Jet Stream that is affected by the ENSO system.

When the sun warms the land and water in the subtropical Pacific areas, warm, moist air rises into the atmosphere. The air has to go somewhere and as it rises higher into the atmosphere it flows south to north, away from the equator. As it moves away from the equator, it cools back down and returns to surface level around 30° latitude. From there, it flows back toward the equator, north to south. This movement of air is called the Hadley Circulation.

Due to the Coriolis Effect, the air current is deflected and moves west to east, like the rotation of the Earth. So, the air current bends eastward and slowly gains speed as it flows north. During El Niño years, the jet stream moves southward and expands eastward due to the warmer ocean waters in the Pacific subtropical region. This movement of the Pacific Jet Stream causes the climate to change during the El Niño events, bringing that warm, moist air to the Southern parts of the United States where the Pacific Jet Stream blows through. However, since the Jet Stream has moved southward, its effects on the central and northern parts of America are lessened bringing drier climates during the event.

While many people associate El Niño with heavier rainfall, it can also cause droughts depending on where you are in the world. The first El Niño event that scientists monitored from beginning to end was the 1997–1998 event. While Peru experienced heavier-than-average rainfall, the Philippines, Malaysia, and Indonesia experienced severe droughts during El Niño. The disparity between different regions and the effects of El Niño are caused by the difference in location of the Pacific Jet Stream, as mentioned above. The Jet Stream influences the overall weather in an area and when it's in its typical location and sphere of influence, the regions affected by El Niño will experience typical weather and climate conditions. However, when the Jet Stream moves, it moves the location of the warm, moist air, changing the climate and weather conditions in affected areas.

In some areas, like Peru and the Southern United States, El Niño brings rainstorms because the Pacific Jet Stream is moved into that area. However, for areas like the Northern United States and even the Phillippines, Malaysia, and Indonesia, El Niño moves the Pacific Jet Stream away from the area, taking the warmer, moister air with it. This movement can cause the climate to become drier compared to the areas that the Jet Stream has moved into. In some cases, it can cause droughts as the air in the area becomes dry and rain becomes scarce. Thus, as we mentioned above, while many places, such as Peru, associate El Niño with heavy rains, it's not a universal truth. Some areas experience droughts.

El Niño also affects the development, severity, and movement of tropical cyclones. Depending on where one is in the world, one might experience a change in the storm system during El Niño or neutral years. The change comes from the shift in the location and direction of the break in the subtropical ridge. Tropical cyclones usually form on the side of the subtropical ridge that's closer to the equator. Then, they recurve into the belt of the Westerlies.

Areas that experience winter tropical cyclones, such as Japan and South Korea, often experience fewer storms during El Niño years. This change in weather events is due to the subtropical ridge moving to around 130° latitude, which favors these locations with the development of tropical cyclones. As the cyclones that develop move across the ocean, they typically don't make landfall in Japan or Korea during the El Niño years before the cyclone dissipates.

Additionally, over the Atlantic Ocean, the vertical wind shear is increased during El Niño years. This change in wind shear inhibits tropical storms from developing at all and leads to less cyclone genesis during El Niño years. Thus, during these events, the Atlantic United States experiences fewer tropical cyclones, such as hurricanes as the storms can't develop and intensify to the point where they would be destructive. This change in the winds is due to the Westerly Winds changing during the El Niño event. However, in the Eastern Pacific basin, the easterly winds have decreased wind shear, leading to higher tropical storm activity. The effect essentially reverses in these locations. The lowered wind shear allows storms to more easily develop and intensify.

Droughts are one effect of El Niño, but flooding is another effect, depending on location. Since El Niño creates both drier and wetter climates, depending on where the winds have moved to, the increased rainfall in some areas can reach a critical point. In some cases, the increased rainfall can be so much so that the area cannot withstand it. Thus, in some areas, devastating floods may accompany El Niño's increase in rainfall. The area most notably affected by El Niño-related flooding is Peru and other areas roughly in the same general latitude level of the globe. The Gulf Coast and Southeastern United States also experience increased flood risks during El Niño due to the increased rainfall.

During the 2023 El Niño event, NASA predicted that flood risks would be even higher than usual, and flooding during El Niño is already more common and devastating than usual. NASA predicted that there would be a higher risk of 10-year floods, warning that the conditions of El Niño could bring up to five 10-year floods that winter. 10-year floods are floods that have a one in ten chance of occurring in any given year, which is to say they're more common than, say, 1000-year floods, which have a 1 in 1000 chance of occurring, but less common than typical flooding. 10 and 1000-year floods are a measure of local sea level. On average, ten-year floods occur five times every fifty years. So, to have five in a year would be extremely unusual and possibly dangerous depending on how bad the flooding got.

As we mentioned above, the entire premise of El Niño is that the temperature of the ocean water in the Pacific increases during the event. This warming of the ocean water is the primary cause of all the weather and climate effects that occur during El Niño years. We don't currently know the exact cause of El Niño's warmer ocean temperatures. However, we do know that it is 100% natural. Instances of El Niño trace back centuries with the earliest recorded instance of El Niño occuring back in 1578. Since then, El Niño has occurred intermittently every two to seven years, with no recurring regular pattern.

We categorize El Niño and determine its presence by a warming of the ocean waters. If the Pacific Ocean average temperature is at least 0.5 degrees warmer for a period of three to five months, scientists will declare an El Niño advisory. During this time, areas that experience wetter weather will be advised to watch for floods, mudslides, and other disasters that may occur due to greater rainfall. Conversely, areas like the Philippines will be put on drought advisory as these areas are more prone to dry weather due to El Niño. During this time, the global climate will shift and everyone will be affected in some way. Global temperatures during El Niño are warmer on average.

This temperature shift can affect things either marginally or greatly. For instance, during the 2010 El Niño event, the Winter Olympics saw impacts on its operations from the warmer temperatures in Vancouver, British Colombia, Canada, where the event took place. Due to the warmer temperatures, the Winter part of the Winter Olympics wasn't quite the same because the warmer temperatures made it harder to maintain the conditions necessary to participate in winter sports without interference.

A landslide occurs when forces on the land cause it to become unstable. One cause of landslides is heavier or prolonged rainfall. The water can erode the sediment holding the land together and cause it to collapse. Then, the land follows the force of gravity, pulling it down from a higher altitude to a lower one. Since El Niño can cause greatly increased rainfall for long periods, landslides occur more easily in locations where the event causes wet weather.

El Niño lasts between nine and twelve months and, in many areas, it causes significantly increased rainfall. During the 1997–1998 El Niño event, landslides were a major disaster that occurred on a much greater scale than even other El Niño events. In some areas, the damage from El Niño-related landslides eclipsed $150 million. The environment surrounding San Fransisco, San Jose, and Oakland, California—one area where multiple slope failures occurred during the 1997–1998 El Niño event—continues to see effects from El Niño to this day despite efforts to aid recovery. During the event, the area received upwards of 43 inches of rain or more than 200% of the amount they normally get. This increase in the water content eroded the land and caused it to collapse.

Warmer ocean temperatures affect the populations of fish, from their locations to their migration patterns. It's no mystery why the first people to notice and document El Niño were fishermen in the 16th century. Their livelihoods depended on the ocean and its bounty. They would be the first to notice when there was a change that affected it. Pacific marine life undergoes many changes during El Niño, including to the fish populations. Fisheries see vastly different yields during El Niño events because the warmer ocean temperatures affect where fish prefer to live and their migration patterns. Similar to how birds fly south to warmer climates during the winter because their food supplies change during the cold months, fish also migrate when the water temperature affects their living conditions.

During El Niño, upwelling stops. Upwelling is a process by which colder, nutrient-rich ocean water from the bottom of the ocean moves upwards. These nutrients help the growth of phytoplankton, the baseline of the marine food web. Phytoplankton are necessary for the marine ecosystem. They sustain most marine life in one way or another and the presence of El Niño disrupts the growth of phytoplankton and, thus, marine life as a whole. Due to the changes from El Niño, many fish migrate to different areas, which changes the diversity of the location. During this time, fisheries may see changes to their yields due to the presence of new fish and competition from migrated populations. After El Niño subsides, the fish tend to migrate back to their original homes as those are the ideal conditions they prefer when El Niño is not heavily disrupting the ocean ecosystem with the warmer temperatures.

Many starfish can live longer in elevated temperatures.

Many starfish can live longer in elevated temperatures.

If you've lived through a heatwave (and who hasn't at this point?), it's important to remember that heatwaves aren't exclusive to land creatures. Water temperature can increase significantly for long periods as well, producing a marine heatwave. Just as heatwaves affect the terrestrial ecosystem, marine heatwaves affect the underwater ecosystem. One of the effects, as mentioned above, is changes to fish migration as they look for more ideal conditions in the altered oceanic climate. However, heatwaves can do the same things underwater that they do above water. Some species are unable to withstand the increased temperatures and die en masse during these events.

Marine heatwaves are worse in the current day because of the fact that global temperatures are rising both above and below sea level. With the already ever-increasing temperatures below sea level, many creatures, such as Snow Crabs, are struggling to coexist with the new conditions. An additional heatwave can be the death knell for these creatures. Snow Crabs in the Bering Strait, in particular, saw a population reduction of 90% during a recent El Niño event. With a population reduction like that, the ecosystem changes wildly as populations previously controlled by the affected animals balloon out of control, causing a domino effect that changes the composition of the area's biodiversity, possibly forever.

One thing people don't consider with El Niño is how the increased temperatures and weather changes affect humans. Due to the wetter conditions, mosquitos and the diseases they carry become a massive risk during El Niño. Outbreaks of malaria, dengue fever, and Rift Valley fever increase during El Niño because the mosquito population flourishes during this time. Areas such as Brazil, Venezuela, and India have cyclical outbreaks of malaria that researchers have discovered are tied to El Niño events and their effects on the weather and climate in the areas. The 1997–1998 El Niño event brought with it a terrifying outbreak of Rift Valley fever in Kenya and Southern Somalia following a period of extremely high rainfall and flourishing mosquito populations.

Outside of mosquito-borne illness, Kawasaki disease increases in Japan and the Western United States during El Niño events. However, we're not sure what the exact impact of the atmospheric conditions of El Niño is on this disease because we don't really know what causes it in the first place.

Additionally, civil conflicts between populations across the globe increased during El Niño due to changes to resource availability during the event. The Amazonian and Bornean forests experience massive changes in plant biodiversity during El Niño events, changing the availability of resources for the populations that live there. In some cases, mass famine has occurred in some areas due to the weather conditions preventing the population from adequately producing enough food for its population, such as the 1876-1878 famines in China, Brazil, India, and Africa that followed the El Niño event that occurred at the time. Researchers analyzed data from 1950 until 2004, revealing that El Niño may have had some effect on the presence of at least 21% of civil conflicts during the time. In affected areas, the rate of civil conflicts between populations doubles from 3% to 6% during El Niño events.