After a short respite from drought conditions thanks to a historically wet 2017 in the San Joaquin Valley, the conclusion of the 2018 water year shows that California may not be out of the woods just yet when it comes to lacking water.
This past precipitation year, which began Sept. 1, 2017 and ended Aug. 31, saw 30.9 inches of rainfall — 5.2 fewer inches than the historical average for the area, or about 85.6 percent of average for the date.
The 2016-2017 precipitation year, in comparison, was the second-wettest ever recorded in terms of rainfall, and was the wettest year on record when it comes to runoff. The year yielded 63.67 inches of precipitation and as of last October had supplied a runoff of 4.86 million-acre feet.
The 30.9 inches of precipitation accumulated in the Tuolumne River Watershed this year was thanks largely in part to the month of March, which provided an ample amount of rainfall with 14.24 inches — nearly half of the precipitation total for the entire water year.
The numbers in March were a cause for celebration at the time, with Turlock Irrigation District Director Charles Fernandes joking that the wave of water March dropped on the region was reminiscent of the “March Miracle,” the stormy March 1991 that launched the beginning of the end of the state’s 1987-1992 drought.
The wet month helped alleviate some of the strain from the dry months of December and February, which saw rainfall numbers that were significantly lower than the historical average. The watershed received just 0.24 inches of rain in December, compared to the historical average of 5.95 inches, and in February received 0.86, compared to the historical average of 5.99.
In 2015-2016, the Tuolumne River Watershed accumulated 39.42 inches of rainfall which was slightly above the historical average. After four years of drought, the numbers at the time were welcomed by local growers and Valley residents alike, TID Utility Analyst Jason Carkeet warned in March 2016 that dry years could be lurking in the years to come and pointed to tree ring data studies as evidence.
The growth rings of tree trunks are one proxy used by scientists to learn about drought-related patterns of the past – thin rings mean growth stunted by a lack of water, while larger rings represent wetter years.
Although the 2015-2016 and 2016-2017 precipitation seasons were above average, the tree ring data shows that there have been many droughts in California’s past that lasted decades – some even lasting for centuries – and many of them had a few wet years sprinkled in between the dry ones.
The 2014-2015 precipitation year was dismal, yielding just 20.92 inches of rainfall, and now in 2018 the numbers appear to be falling.
In 2016, Carkeet believed the state may be in the middle of a similar drought, finding relief in a couple of above-average rainfall years.
“To come out and say, ‘Hey, we’re on our way out if this,’ that would be foolish I think,” said Carkeet at the time. “Not foolish, but naïve maybe.”