What could El Niño mean for low water levels at Lake McClure?

Merced farmers and officials at the Merced Irrigation District hope the predicted El Niño weather pattern drops a lot of water, covers the Sierra Nevada with snow and Lake McClure reaps the benefits.

After last year’s record-low snowpack, the water level at Lake McClure is less than 11 percent of capacity, MID reported. Data from the California Nevada River Forecast Center show the reservoir now holds about 106,799 acre-feet of water, compared to the 665,000 acre-feet that MID says is average. That’s the second driest on record for the reservoir, and will likely be the driest for a three-year accumulation, according to the forecast center.

Even though meteorologists say there are strong signs indicating El Niño, that doesn’t mean it will dump water on the Valley. It could bring rain totals up to average, said Kevin Durfee, a meteorologist at the National Weather Service in Hanford. “We can say with confidence that rainfall this winter will be above that of the last two winters,” he said. “It may just be normal.”

“Like everybody else, we are watching and waiting to see what happens,” said Mike Jensen, a spokesman for MID.

But, with the current water levels, El Niño would need to drop more than it did in the Valley’s wettest years to fill up Lake McClure, said Alan Haynes, a hydrologist at the California Nevada River Forecast Center. The wettest year on record was 1983, he said, and Lake McClure received 270 percent of its average runoff, or 2,781,000 acre-feet.

“There’s no guarantee a strong El Niño will give a wet year,” he said.

When Valley residents think of El Niño, they likely recall the rainy season of 1997-98. That year, MID made continuous flood releases from McClure and received about 1,800,000 acre-feet of water, Jensen said. Lake McClure’s capacity is 1 million acre-feet.

Because the mountains had a dense snowpack from 1996 and the El Niño brought warm rains, the Valley and other parts of the state saw heavy flooding in 1997-98, Durfee said.

“A lot of times, extreme flood ends extreme drought,” he said. But, the current circumstances are not the same as they were for the winter that characterizes El Niño for Valley residents. This year, the Sierra Nevada is starting out with no snowpack.

So far in 2015, Lake McClure has received about 164,000 acre-feet of natural flow runoff. That’s 16 percent of an average year. Plus, the central Sierra is facing about a year’s worth deficit of rain, Haynes said.

Because of the dry conditions, any rain the Valley gets may cause problems with runoff. “The good thing is it won’t take too long for the soil to become porous,” Durfee said.

In the mountains, if it’s cold enough, snow would accumulate, “which is what we want,” he said.

In short, Durfee said: “There is no way of knowing how this El Niño is going to pan out.”

This story was originally published August 7, 2015 at 6:35 PM with the headline "What could El Niño mean for low water levels at Lake McClure?."