El Niño or el nada?

Michael Raffety

4-21-14

As El Dorado Irrigation District Director George Osborne noted at the April 14 board meeting an El Niño could go south on us. Osborne, retired as a local commander of the California Department of Forestry and Fire Protection, had a professional interest in the weather.

Predictions that we might have an El Niño year in 2014-15, brought Osborne’s reminder that sometimes El Niño ocean conditions send the rain into Arizona instead of Northern California.

It wasn’t until the 1982-83 rain year that scientists began talking about El Niño. It was only a few years prior to that the Scripps Institution of Oceanography would issue long-range forecasts in the fall for the winter. The 1982-83 rain year was the second wettest on record bringing 72.85 inches of rain, higher than a 6-foot-high person. The record was set in 1889-90 at 78.13 inches, enough to drown a 6-foot-5-inch basketball player standing in a rain barrel.

Now Scripps, by studying tree rings, has determined that El Niños have been happening for 700 years.

“I think there’s no doubt that there’s an El Niño under way,” said climate scientist Kevin Trenbeth of the U.S. National Center for Atmospheric Research. “The question is whether it’ll be a small or big one.”

Oceanographers have improved monitoring of ocean temperatures and other conditions, so that at this point they can say there is anywhere from a 50 to 80 percent chance we will have an El Niño affecting us in the 2014-15 rain year. They’ll be more sure by June, but the real proof will come in the fall and winter.

What happens is normally the trade winds in the Pacific Ocean blow east to west, leaving the Pacific Coast of North and South America with cold water. When the trade winds reverse, warm water heads east toward the Pacific Coast. Fishermen in South America, noting its appearance around Christmas, call it El Niño, the Christ child.

“The main question right now is if this entire warm-pool region will accelerate to the eastern basin or stick in the middle of the Pacific,” said meteorologist Michael Ventrice of Weather Services International.

“Official NOAA Climate Prediction Center estimates peg the odds of El Niño’s return at 50 percent, but many climate scientists think that is a lowball estimate. And there are several indications that if it materializes, this year’s El Niño could be massive, a lot like the 1997-98 event that was the strongest on record,” said Adam Mann on his Website “Wired.”

The 1996-97 rain year saw a 500-year flood on rivers in El Dorado County as the North Fork of the Cosumnes overtopped the Bucks Bar Bridge and the South Fork of the American River saw a house and propane tanks swept away. The river lapped at the bottom of the Mosquito Bridge. Portions of Highway 50 through the American River Canyon were cut away by the river, which rolled boulders along, leaving a house-sized one on the highway. That year only wound up with 50.71 inches of rain, but December saw 19.23 inches fall and January saw 19.22 inches. It felt like all 19 inches fell between New Year’s Eve and New Year’s Day.

Like the 1982-83 year, the 1997 flood left Highway 50 covered by a slide. In 1983, the slide came from the north side of the highway. In 1997, it came from the south and slopped across to Highway 50. It knocked out a few cabins in the Randall Tract. Wrights Lake Road was blocked from Highway 50 by a slide that year as well.

“El Niño is a recurring weather pattern affecting the world every two to seven years,” Mann wrote.

That recurring pattern got my attention, so I reviewed our 139 years of rainfall records to see if it confirms the pattern Mann pointed to. I looked at every year that totaled more than 50 inches of rainfall. The average rainfall in Placerville as of the 2012-13 rain season is 39.57 inches. In 139 years there have been 26 that recorded 50 inches and above. Two of those, as mentioned previously, recorded more than 70 inches and seven recorded more than 60 inches (but less than 70 inches).

The intervals for big rain years, beginning with 2011-12 and going back to 1876-77, bear that out for the most part. The intervals are six, six, 11, 13, 15, 25, four, seven, three, three, four and three.

Some of these 50-inch-or-better rain years clump together in twos and even in threes, such as 1982-85. But a super clump was the four years of 1892-97.

The real anomaly is the 25-year break between 1910-11 and 1935-36. Two other breaks of lesser amounts were the 15 years between 1935-36 and 1950-51. The years 1950-52 were a two-year clump, with the winter of 1952 being a record snowfall year that saw Southern Pacific’s City of San Francisco snowbound in the Sierra.

Another 13-year hiatus followed the year 1955-56 until 1968-69. The former year was a flood year for the Sacramento area. Then there was an 11-year break between 1984-85 and 1995-96. That can be whittled down to 10 years if one counts the 49.55 inches that fell in 1985-86. The year saw 18.87 inches fall in February, with 10 inches of that falling in a 10-day period. Here’s what Sacramento County’s stormready.org said about that: “The overwhelming floodwaters tore bridges from their foundations and punched through levees. The Northern California flood resulted in 13 deaths, 50,000 people evacuated and over $400 million in property damage.” Folsom Dam was nearly overtopped and that is why an emergency overflow flood bypass is being built at Folsom Dam, thanks to former Congressman John Doolittle.

Though the average rainfall in Placerville is 39.57 inches, that is skewed by the big water years when we get more than 40 inches. The norm tends to be between 28 and 33 inches. Anything above 25 inches is an adequate rain-year. The trick is to have a way to bank the big water years. The El Dorado County Water and Power Authority plans to do that by laying claim to 40,000 acre-feet of area-of-origin water and sell it to Sacramento until our county needs it. Sacramento would bank it in an underground aquifer, something that can’t be done in the foothills. That’s one way to save during big rain years. The El Dorado County Water Agency and the El Dorado Irrigation District need to figure out another way to capture runoff in El Niño years and bank it in a one of Sacramento Municipal Utility District’s reservoirs or a new reservoir or then figure out how to feed that banked water back into the system.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s