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Special Report

by Ralph Wagner

Towards El Niño and Lake Arrowhead Some of the interest in the El Niño that is anticipated to occur starting now, or more likely in January 2016, and lasting through March of April 2016, stems from its dry sibling, La Niña, that has held sway for the past four years. La Niña has allowed the level of Lake Arrowhead—the barometer of everything that is good about Arrowhead Woods—to drop below elevation 5,100 feet. But the “strong” El Niño that is going to fill the lake in February 2016 will change all of that. It always has—historically—before. I’m sure this history will repeat itself. The History of El Niños at Lake Arrowhead It apparently wasn’t until the 1951-52 water year that meteorologists recognized there was a phenomenon in the equatorial Pacific Ocean, called an El Niño, that, in varying degrees, could exert a profound influence on above median precipitation across the southern tier of the U.S. The California State Department of Water Resources, for instance, published some charts in 1997 showing relationships between stream flows in the Santa Ana River and El Niño years from the 1951-52 water year through Sept. 30, 1997, and predicted an El Niño in the 1997-98 water year. Sure enough, from Oct. 1, 1997, through Sept. 30, 1998, precipitation at Lake Arrowhead measured 71.58 inches—188 percent of the 122-year average—or a “strong” El Niño. This was not as strong, however, as the “Godzilla” El Niño at Lake Arrowhead in water year 1968-69 at 98.10 inches of precipitation. What is an El Niño and how is it measured? When the temperature of the Pacific Ocean water off the coast of Peru becomes greater than about 2.7° F warmer than normal, or approaches that, an El Niño is said to exist. This, along with a shift in the trade winds from the east to ones from the west, allows the Pacific water to produce more storms that are pushed eastward by jet stream winds from the west to the east. It is likely, of course, that these El Niño conditions occurred in years prior to their being recognized by meteorologists in 1950. El Niños don’t regularly occur every five years, because Mother Nature is fickle. They can be back-to-back (rarely) or as far apart as 13 years (also rarely). Many are in the seven to 10-year range. El Niños at Lake Arrowhead can be weak, moderate, strong or very strong, depending on the amount of precipitation, generally above 120 percent of normal, its range and distribution in the months from November through March. The 124-year average or normal precipitation for the Lake Arrowhead area is about 38 inches per water year. I would classify an El Niño to be weak at Lake Arrowhead when precipitation is in the range of 47 to 51 inches in a water year, or about 127 percent of normal. This has happened about four times in the 124-year period of record: 1894-95, 1910-11, 1978-79 and 1985-86. Moderate El Niños happen here when precipitation is in the 52 to 61-inch range, about 146 percent of normal. There are seven water years when this happened: 1906-07, 1921-22, 1934-35, 1942-43, 1944-45, 1965-66 and 2010-11. Strong El Niños have taken place eight times: 1936-37, 1940-41, 1951-52, 1957-58, 1979-80, 1982-83, 1994-95 and 1997-98. Precipitation has ranged from 63 to 76 inches, about 185 percent of average. Predictions have been that this coming El Niño will be larger than the 1997-98 El Niño, when 71.58 inches of precipitation fell. Five very strong El Niños in the range of 79 to 98 inches of precipitation have taken place in Lake Arrowhead. The largest occurred in 1968-69 when a total of 98.10 inches of precipitation fell, with 46.02 inches falling in January and 35.84 inches in February. The next largest was in 1977-78 (91.34 inches), then 1992-93 (90.88 inches), with the precipitation falling in January and February. All of the El Niños at Lake Arrowhead have had one thing in common: They have all brought the lake back to a full and overflowing condition. From the time the lake first became full in the 1921-22 water year, there have been 20 El Niño events, recurring, on average, about every 4.65 years. They have averaged about 69.27 inches, which would be in the range of a strong El Niño. From 1921-22 to 2014-15, the average annual precipitation has been 38.02 inches. Fifty-five of those years have been below average, 38 above average. Historically, during El Niño years, most of the precipitation occurs in the months of January, February and March. On average, about double the normal amounts for each of these three months happens when El Niño arrives. Sometimes November can be a big month—1965, 29.99 inches—or December, such as 2010 (26.70 inches). In most El Niño precipitation events, storms are not extremely intense, but follow each other closely, usually at rates not exceeding about five inches in 24 hours and sometimes as great as about 10 inches in 24 hours. What Does This Year Hold? My prediction, at this time, is that the current 2015-16 water year will be a strong El Niño year, possibly with November bringing about six inches; December, about 11 inches; January, about 14 inches; February, about 14 inches; and March, about 12 inches for a total of about 57 inches. This will be more than enough to cause the lake to become full and overflow, probably in February 2016. I don’t expect this to be a Godzilla El Niño year at Lake Arrowhead nor the strongest El Niño ever, but the total precipitation from Oct. 1, 2015, through Sept. 30, 2016, will be in the range of 63 to 76 inches, probably averaging about 66 inches or about 175 percent of the 124-year average for Lake Arrowhead. El Niños are always followed by their dry siblings, La Niña, and it is these La Niña conditions over three to four-year periods that cause the lake level to drop below elevation 5,100. To me, prudence and common sense would suggest that, once the lake becomes full and stops overflowing, let’s start putting water back in it through indirect potable reuse so that it doesn’t drop below elevation 5,100 before the next El Niño fills it again.