El Niño is back, and it's a force to be reckoned with. This oceanic phenomenon, which typically alters global weather patterns, is now charging full steam ahead, potentially drenching California like never before. With the National Oceanic and Atmospheric Administration (NOAA) declaring it likely to strengthen significantly through the end of the year, this El Niño could be the strongest on record. The stakes are enormous for a state already grappling with its warmest winter on record.
Daniel Swain, a climate scientist with the California Institute of Water Resources, warns that this El Niño has no signs of slowing down. "The observed trajectory is a little bit faster even than some of the already very aggressive forecasts from a few months ago," Swain said. "All signs point to full steam ahead."
For the rest of the world, this El Niño could be a preview of a new climate reality. Even moderate El Niños temporarily warm global temperatures; a strong one, coupled with climate change, will likely push global heat records to new heights. This is a critical moment in our understanding of climate change and its impacts.
What is El Niño?
At its core, El Niño is about warm water. Every two to seven years, sea surface temperatures in the eastern and central Pacific Ocean along the equator rise well above normal, setting off a chain reaction that reshapes weather patterns around the globe. Under normal conditions, steady trade winds blow from east to west along the equator, pushing warm surface water toward Indonesia. These west Pacific waters are normally the hottest in the world.
During an El Niño, those trade winds weaken or even reverse. Warm water sloshes eastward across thousands of miles of open ocean, and the cold upwelling off Ecuador slows or shuts down entirely. The surface of the tropical Pacific transforms from a cool spot into a massive pool of anomalous warmth thousands of miles across. This warm water heats the air above it, fueling more thunderstorms, lowering atmospheric pressure, and altering the arrangement of pressure systems and the jet stream worldwide.
Why This El Niño Could Be Historic
The current numbers coming out of the tropical Pacific are startling. The Oceanic Niño 3.4 Index, the sea surface temperature in an area of the ocean along the equator south of Hawaii, has surged to +1.8 degrees Celsius as of early July, having climbed from +0.48 degrees Celsius in April. This alone would make it the fourth or fifth most intense El Niño over the past 40 years, with more expected strengthening on the way. These sea surface temperatures are almost 3.5 standard deviations above average for this time of year, the equivalent of a once-in-4,000-year event under normal conditions.
What Can a Super El Niño Mean for California?
For California, a very strong El Niño arriving atop record-warm ocean temperatures along the Pacific Coast means the stakes are compounded. Warmer storms, higher snow lines, more rain at elevation with less snow, and more intense atmospheric rivers carrying more moisture. Rainy winters are the most well-known consequence of El Niño on California. When El Niño displaces the jet stream southward, it steers a parade of Pacific storms, including moisture-heavy atmospheric rivers, directly into the state.
A notable example was in February 1998. During one of the strongest El Niños on record, three consecutive major atmospheric rivers brought record-breaking precipitation to nearly all of California, causing widespread flooding and catastrophic mudslides. For the Central Valley and Sierra, the question is not just how much precipitation falls but the form it takes. Warmer ocean waters mean El Niño storms tend to be warmer, allowing them to physically hold more moisture. That pushes the rain-snow line higher up the mountains, meaning some precipitation that should be piling up as snowpack instead runs off as rain.
California learned that lesson the hard way this past water year. The state received near-average precipitation in many areas, but the April 1 snowpack was the second-lowest on record at just 18% of normal. In the Northern Sierra, it was an astonishing 6% of normal. A strong El Niño could deliver even more precipitation this coming winter, but if the storms are warm, the Sierra snowpack may fail to recover even in a wet year.
Increased Fire Risk Next Summer
A downstream consequence of a wet El Niño winter is what comes after. Heavy winter rains fuel explosive vegetation growth across California’s foothills, grasslands, and forest understory. By next summer, as temperatures climb and the dry season takes hold, all that lush greenery will become fuel. California saw exactly this cycle play out recently. A wet El Niño-boosted 2024 spring produced a burst of vegetation growth across the Northern California foothills. When heatwaves arrived in June and July, the growth dried out rapidly. The Park Fire ignited near Chico on July 24 and became the fourth-largest wildfire in state history, burning more than 429,000 acres across Butte and Tehama counties.
A super El Niño winter in 2026-27 could set the stage for a similar, or worse, fire season in the summer of 2027, especially if the climate pattern transitions to La Niña afterward, which tends to bring hotter, drier conditions back to California. This highlights the complex and interconnected nature of climate impacts.
Conclusion
El Niño is back, and it's a powerful force that will significantly impact California and the world. As Swain notes, "It pretty dramatically shifts the odds when it is strong. It’s a shift both upward on the wet side and downward on the dry side." This El Niño is not just a weather event; it's a critical moment in our understanding of climate change and its impacts. As we navigate this complex and interconnected world, it's essential to listen to the experts and prepare for the challenges that lie ahead.
