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El Niño may mean more rain or another dry spell
• Water year ends as third wettest in recent history
El Nino map 2023
This graphic, based on information from the National Oceanic and Atmospheric Administration (NOAA) and Climate Prediction Center (CPC), shows how precipitation may play out for the Central Valley and the rest of the United States.

The region is off to a sluggish start just over a month into the 2023-24 water year. Then again, the 2022-23 water year didn’t get off to a roaring start either and it turned out to be third wettest year since Turlock Irrigation District began keeping records in 1897.

With 4.13 million acre-feet of runoff, 2023 ranked behind 2017 (4.6 million acre-feet) and 1983 (4.6 million acre-feet).

On average, the Tuolumne River Watershed gets about 2 million acre-feet per water year, which starts on Oct. 1 and concludes on Sept. 30. To bring that into finer focus, Don Pedro Reservoir can store 2,000,030 acre-feet of water. So, 2023 provided more than double the usual amount of precipitation and more than double what Don Pedro Reservoir can handle.

“Coming out of this historically wet year, we’re in a great place,” said Brandon McMillan, communications specialist for TID. “Having a full Don Pedro going into this next year is, obviously, a really positive outlook for our irrigation season in 2024.”

According to McMillan, the TID board of directors typically will receive staff recommendations beginning in February — depending on the water year — and make a decision in March regarding the start of the irrigation season.

Paradoxically, TID’s precipitation year begins a month earlier than its water year — staring Sept. 1 and concluding Aug. 31 — and through Nov. 6, the Tuolumne River Watershed has received less than inch of rain (0.91) so far.

However, the coming El Niño could have an impact this winter.

“I’ve been closely following the ongoing development of El Niño since last spring … and so far, long-lead predictions of where we’d be by November have pretty much been spot-on,” UCLA climate scientist Daniel Swain, Ph.D., said on his website, “A strong and still-strengthening east-based El Niño was predicted for November 2023 — and that’s exactly what we’ve got right now.”

Swain used ocean-atmosphere models — the North American Multi-Model Ensemble (NAMME) and the International Multi-Model Ensemble (IMME) — to help make sense of the data.

“So, what are (they) telling us?” said Swain. “Well, the latest update cycle (Nov. 8) paints a pretty striking picture of what might occur across North America this winter. The NMME has actually trended quite a bit wetter across most of California for the December-March period, depicting a relatively high statistical likelihood of wetter-than-average conditions across Central and Southern California — with a more modest tilt in the odds toward wetter-than-average conditions in Northern California, as well. The IMME shows a similar pattern, but with decreased amplitude and statistical confidence.”

The Tuolumne River Watershed — 1,500-square miles of mountainous area above Yosemite — can see both sides of El Niño.

“El Niño can cause wet conditions in certain portions of the state and the U.S., and create dry conditions in portions of others,” said McMillan. “Our watershed is situated in kind of a strange place. It’s on the cusp of where we can experience either of those types of conditions.”

McMillan went on to say that whatever scenario materializes, TID is ready.

“We use state-of-the-art modeling to determine how the precipitation will come, how it will impact watershed, and how it will run off,” said McMillan. “We’re treating this like any other year, really. We’re focusing on various scenarios, along with the eight- and 16-day forecasts, to see what action materializes.”