As El Niño tightens its grip on the United States, we might be in for a very wet and snowy winter.
Historically, El Niño has seen high levels of precipitation across the West, as well as parts of the South, with similar patterns being forecast for this winter, according to maps released on the National Oceanic and Atmospheric Administration (NOAA) ENSO blog last week.
The maps show that California and Nevada are due to face above-average precipitation—representing both rain and snow—this winter, while Florida, Georgia, Louisiana, and other southeastern states are also forecast high levels of precipitation. These predictions represent an average of hundreds of possible forecasts, however, so they may not represent exactly what will happen in the coming months.
El Niño is a climate pattern that occurs in the Pacific Ocean once every two to seven years. It results from weakened trade winds combined with warming ocean temperature, causing warmer waters and the Pacific jet stream to be pushed toward the West Coast. This can lead to strange weather events across the U.S., depending on the strength of the El Niño event.
"An El Niño event favors wetter winters across the south and the southwestern United States and drier and warmer winters in the Pacific Northwest," Aaron Levine, a research scientist at the Cooperative Institute for Climate, Ocean and Ecosystem Studies at the University of Washington, previously told Newsweek.
The NOAA maps show that the precipitation forecast for this coming winter (December 2023 to February 2024), based on the average of all the individual models in the North American Multi-model Ensemble forecast system, closely matched the geographic pattern of precipitation we'd expect based on averaging past El Niño winters from 1952-2022.
"Strong" El Niños are defined by seeing water temperatures of at least 1.5 degrees C [2.7 degrees Fahrenheit] above average, while "historically strong" events lead to a 3.6 degrees F temperature anomaly above the mean.
The U.S. Climate Prediction Center (CPC) recently predicted that there is a 35 percent chance of a "historically strong" El Niño between November 2023 and January 2024, with more than a 55 percent chance of at least a "strong" El Niño through January to March 2024.
Additionally, the stronger the El Niño or La Niña, the more likely that the actual winter pattern will match the average model forecast pattern of high precipitation. This may lead to increased flooding in the affected areas: up to five "10-year flood events"—floods so large that they have a one in 10 chance of occurring in a given year—may occur in places like Seattle and San Diego. Ten-year flood events are also a measure of how high local sea levels have become.
La Niña is the counterpart to El Niño, where stronger trade winds cause colder waters to upwell off the U.S. West Coast, leading to warmer winter temperatures in the South and cooler temperatures than normal in the North, as well as stronger hurricanes.
"Over the last three years, due to the La Niña effect, the global average surface temperature (GMST) barely showed noticeable growth. Following this El Niño event, the rate of temperature increase in GMST has been significantly amplified," Fei Zheng, an associate professor at the Institute of Atmospheric Physics, Chinese Academy of Science, told Newsweek.
As a result of this stronger El Niño, there is a 95 percent chance that the global average surface temperature this winter will set a new record high, a recent study in the journal Advances in Atmospheric Sciences revealed.
The El Niño this year is therefore expected to accelerate the heating of the planet, pushing us closer to the 1.5 degrees C climate change threshold agreed at the 2015 Paris COP21 climate conference.
El Niño's Effects on Precipitation May Be Influenced by Mountains
A paper this week in the journal Nature Water has revealed that mountains amplify and obstruct precipitation caused by strong El Niño and La Niña events, leading to more rainfall in the West and less in the East.
"Because of the seasonality of precipitation in the West, most of it falls during the winter. If you can predict how much precipitation you'll have in the winter, you'll have a good sense of what your summer dry period will look like in terms of your water allocation," James Stagge, lead author of the study and an assistant professor of civil, environmental and geodetic engineering at The Ohio State University, said in a statement.
"All the rain falls on the west side and then by the time it gets to the east side of the mountains, there's no more moisture to fall," Stagge said. "Add in the effect of ENSO and it's just like a multiplier, so the wet side gets a lot wetter during El Niño in the south, and much drier during La Niña."
This discovery may help in water conservation efforts along the drought-ridden Colorado River.
"Anything we can do to improve our ability to predict how much water we'll get during this critical period allows cities, farmers, water managers and member states of the Colorado River Compact to prepare for upcoming drought and potentially start to go into conservation ahead of time so they're not caught flat-footed," Stagge added.
"Water is a determining factor in western North America. It drives the economy, it drives extremely large cities, and all of these stakeholders are concerned about it," he said. "If we're able to better understand or in some cases predict precipitation in this part of the world, then we have a better chance of preparing for water shortages."
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Jess Thomson is a Newsweek Science Reporter based in London UK. Her focus is reporting on science, technology and healthcare. ... Read more
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