Over 40 years ago, Tucson residents woke up to find their houses being swept away by rivers that didn’t exist the night before. The year was 1983, and the muddy waters of the normally-dry Santa Cruz River churned violently, carrying away buildings, property, and people.
Tropical Storm Octave, which hit in October of that year, was the primary cause of the flood. But there was something else that contributed to Octave’s strength and the path it took through the Southwest.
It was a “Super” El Niño year.
El Niño is an atmospheric phenomenon that happens when the Pacific Ocean gets unusually warm. That warm water shifts weather globally, making some areas hotter and drier, while others become colder and wetter. The effects tend to become more pronounced as the speed and scale of that oceanic warming increases.
That 1983 El Niño, which helped bring the storm that caused the destructive floods, was one of the strongest “Super” El Niños on record. That year, the temperature of the Pacific Ocean was about 2.2 degrees Celsius above normal.
In 2026, another Super El Niño is developing, with forecasts projecting ocean temperatures of up to 3.4 degrees above normal. It could be the strongest El Niño ever recorded.
So what does that mean for Tucson?
Wetter winter, hotter summer?
Generally speaking, El Niño years are expected to bring cooler, wetter falls and winters to the Southwest. That’s because the Pacific jet stream gets pulled south, bringing storms to Arizona instead of the Rocky Mountains.
Dr. Kim Wood, an associate professor of hydrology and atmospheric sciences at the University of Arizona, generally concurs with the expectation of more winter storms. But they said it’s still difficult to predict the weather.
“On a day-to-day basis, there are many factors that can affect exactly where a storm ends up going once it forms, and that's the part that's harder to predict many months out, especially as this El Niño episode is still unfolding,” they said.
Not every El Niño has brought the expected conditions to the Southwest, and scientists say it only accounts for about a third of variation in winter rainfall in the region. For example, the 2016 El Niño winter, which matched the intensity of the 1983 event and is one of the strongest to date, brought lower-than-average winter precipitation to the Tucson area.
Dr. Jeffrey Shaman, a professor and senior vice dean at Columbia University’s Climate School, said that in addition to changes in winter weather, strong El Niños typically cause a rise in global temperatures. That’s because all that excess heat in the ocean gets diffused into the atmosphere.
“It does mean that it's likely that our summer, next summer, is going to be very hot. And the risk that some of the areas will have heat waves that might be particularly difficult to deal with is going to increase,” he said.
That heat diffusion takes time, which is why many of the hottest years on record — 1997, 2016 and 2024 — have happened after strong El Niños. Shaman says there isn’t any guarantee that Arizona will bear the brunt of that excess temperature, but the likelihood of higher temperatures globally is “quite likely”.
“Unusual level of consensus”
Though it’s too soon to tell what exact effects it will have on local weather, according to Shaman, this El Niño is very likely to be the strongest ever observed at this point in the year.
“We have a lot of models that we use to forecast this. They're generated in Europe and Japan, in China, in the U.S., U.K., etc. And there's an unusual level of consensus,” he said. “We haven't seen this before, where they're really all agreeing with the same outcomes.”
Those models are not a guarantee of weather patterns to come, but the fact that they all agree means that “there's a higher likelihood that it's going to be wetter than normal in the Southwest, including in particular Southern Arizona,” said Shaman.
Both Wood and Dr. Shaman said that comparing this year to previous cycles is challenging, because the speed and magnitude of this year’s event is so unprecedented. Both said there was no true analog to what scientists are observing in 2026\.
In any case, they said, it’s important for communities to be prepared for anything.
“Seeing this Super El Niño… That is an encouragement to keep an eye on the sky, to watch how things \[are\] unfolding, because we know that we've seen past events that have flooded, which means it's good to be more aware. But we're not guaranteed that that will happen,” said Dr. Wood.
How Tucson is preparing
The Pima County Flood Control District can’t say for sure whether Tucson will see flooding this winter. But they say that things have changed since 1983\.
Lynn Orchard, Division Manager of Watershed Studies at the Flood Control District, said the district’s work has made similarly large flooding events go nearly unnoticed.
“There hasn't been anything similar to 1983\. That was an anomalous storm event across the western United States — it's a landmark,” he said. “But Pima County has not not experienced major floods since then, and the fact that people don't think about it very often is a reflection of the work the Flood Control District has done.”
As he spoke, Orchard sat in front of two antiquated floppy disks, relics from one of the city’s first responses to the 1983 floods — the creation of an alert system to warn residents of large amounts of rainfall. Unlike weather forecasts, the alerts are tuned to devices which measure the rain that actually hits the ground, making them more accurate in capturing the actual risk of flash flooding. Since then, the Flood Control District has expanded that alert system, strengthened banks and purchased vulnerable properties in areas at risk of flooding.
Orchard says evidence of the Flood District’s success can be seen in the historic floods of 1993, in which the city received similar levels of rainfall but only suffered about \$17 million in damages, versus the over \$100 million sustained in the 1983 floods.
FEMA recently designated the Flood District as a Class-2 Community — which is an award for Pima County “going above and beyond the federal minimum requirements for floodplain management,” according to the Flood District. The classification means that residents of unincorporated Pima County can get up to a 40% discount on flood insurance premiums. The City of Tucson, by contrast, gets a Class-6 rating — a few notches lower on the ordinal scale.
Orchard says the Flood District’s work will continue as normal, no matter what this year’s El Niño brings.
“We're very aware that the Super El Niño is happening. It's going to cause increased variability in weather patterns, and that's just something that we've got baked into our mindset here with the changing environment, whether it's Super El Niño or the myriad of other factors,” Orchard said. “So it's just business. We keep cranking, keep trying to keep people safe.”
According to the Flood District, the best thing Pima County residents can do to prepare is stay informed by contacting their local floodplain administrator — for Tucsonans, that’s the City of Tucson and for Unincorporated Pima County residents it’s the Flood District. Those administrators can help give residents information on whether their property is in an at-risk area, and help them create a plan in the event of a flood.
Residents in areas with high flood risk can also sign up for the county’s flood alert system, and should prepare an emergency bag with supplies for three days in the event they need to evacuate their home.
The Flood District also advises residents in these areas to plan alternative routes and family meeting points in the event of a severe flooding event, and to ensure they have flood insurance for their homes.
