So long to a hot year

Michael Raffety

2-9-15

At the end of each calendar year, we total up the average monthly temperatures to see what the overall average daytime and overnight temperatures for the year are.

As most of you might have guessed, after the fourth driest rainfall year on record here (Jul, 1, 2013-June 30, 2014) the year was generally warm. Totaling up monthly temperature averages by calendar year rather than rainfall season, we found the yearly average of monthly temperatures for 2014 was 80.0 degrees F. That is downright toasty.

Leading off was January 2014, which recorded eight days above 80 degrees, making for a monthly average of 73.8 degrees that January.

The January average from 1999 through 2014, after adding in January 2014, was 55.8 degrees. That is radically different from 73.8 degrees. (We have incomplete temperature records for 2013 and no records for 2011 and 2012 after PG&E cut us off after supplying records since 1928).

To put the 80-degree calendar year average in context, the 10-year average from 2000-2009 was 72.56. In 2010, the last full year of temperature recordings until we established our own weather station here part-way through 2013, the average for 2010 was 72.9 degrees.

The overnight temperature average for 2014 was a little warmer than usual as well at 50.1 degrees monthly average for the calendar year. That compares to the 10-year average of 47.17 degrees for 2000-2009. In 2010, it was 47.7. Not as dramatic as 80 degrees.

This January set a record by recording no rain. On Jan. 27 it rained enough to wet the Mountain Democrat parking lot twice and leave everybody’s windows spotted and dirty. But that rain didn’t even knock the dust out of the Mountain Democrat rain gauge. This is the first January in 141 years that has failed to record any rain. Until now the lowest rainfall for January was .015 inch in 2012, with the rainfall totaling 29.51 inches for the 2011-2012 rain year.

January averages 7.41 inches of rain, according to the Mountain Democrat’s 140-year rainfall record. There have been four other Januaries in 141 years that have recorded less than an inch of rain. There is no pattern indicated by these. In third place is 1984 that saw 0.42 inch of rain in January, but the rain year totaled 43.49 inches. Fourth place is 0.45 inch in January 1918, which finished the rain year with a low but adequate 25.97 inches. Fifth place is 1976 with .062 inch in January, with the rain year being the second driest on record at 15.9 inches, Sixth place is  0.63 inch in 1991, with the rain year totaling an acceptable 28.63 inches.

We’re not doing too bad, despite the goose egg for January. We have recorded 13.31 inches of rainfall since July 1, 2014. At the end of January 2014 the rainfall total Since July 2013 was 2.31 inches — 17 percent of what we have recorded so far this year.

The big reservoirs like Shasta and Folsom were down in the low 30s in percentage terms and have come up to 45 percent for Folsom and 42 percent full for Shasta, but the dry January has slowed down the tributaries that help fill those reservoirs as well as the Upper American River Project reservoirs of Sacramento Municipal Utility District.

The maximum for January was 28.76 inches set in 1911. In 84 out of 144 years, January rainfall has been 5 inches or greater — 58 percent of the time.

We’ll need to triple our current 13.31 inches of rain to have a shot of filling the reservoirs. If that is tripled we would come in a little over the 140-year average of 39.43 inches.

If the Auburn Dam had been built it would have held 2 million acre-feet, double the size of Folsom Lake. Auburn would have yielded 300,000 acre-feet of consumptive water. With a dry January, we may not think about flooding, but it could happen even this year. Folsom provides 213-year-flood protection 64 percent of the time, while Auburn Dam added to Folsom, according to former Congressman John Doolittle, would have provided 400-year flood protection.

In 1986 when February rainfall totaled 18.87 inches, Sacramento and Rancho Cordova barely escaped flooding and Folsom barely escaped being overtopped. That is why the billion dollar  overflow chute is being constructed on the south side of Folsom Dam.

We don’t have to worry about a repeat of the 1997 flood that overtopped the Bucks Bar Bridge and the Chili Bar Bridge and swept a few houses and propane tanks down the South Fork of the American River and destroyed part of Highway 50 in the American River Canyon. That 1997 event resulted from 19.23 inches of rain in December followed by 19.22 inches in January, with most of it falling on New Year’ Eve and New Year’s Day.

Here’s hoping a big February and March bring our totals above 25 inches and preferably more than 30 inches.

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