After a lackluster amount of rainfall throughout the San Joaquin Valley in 2018, the recent end to the 2019 precipitation year was a welcome sight for community members wary of drought thanks to plenty of storms that brought above-average numbers.
This past precipitation year, which began Sept. 1, 2018 and ended Aug. 31, 2019, saw 45.65 inches of rainfall — nearly 10 inches more than the historical average for the area or about 125 percent of average for the date.
“It’s well above average and it’s well above what we did in 2018,” Turlock Irrigation District Utility Analyst Olivia Cramer said during Tuesday’s Board of Directors meeting.
The encouraging numbers come just a year after the less-than-stellar 2018 precipitation year, which saw 30.9 inches of rainfall from Sept. 1, 2017 to Aug. 31, 2018. That was 5.2 fewer inches than the historical average and only 85.6 percent of average for the date, showing that despite the record-breaking water year in 2017, a lack of water is always a concern in California.
The state’s yo-yoing precipitation levels from year to year are no surprise to scientists, who keep expectations of approaching dry years realistic by studying the growth rings inside of tree trunks. Thin rings mean the tree’s growth was stunted along the way by a lack of water, while larger rings represent wetter years.
Tree ring data shows that there may 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 2019 precipitation year was indeed a wet one and a majority of the period’s 45.65 inches of rainfall came in February when a series of storms swept through the region. The storms brought 13.7 inches of rain during the month, which was seven inches more than the historical average for the month.
In fact, five of the 2019 precipitation year’s 12 months saw rainfall totals that surpassed the historical average, including November (7.18 inches), January (6.66 inches), February, March (7.91 inches) and May (5.65 inches).
The state was also declared drought-free for the first time in nearly a decade in February, thanks to a surging snowpack that was 152 percent of its historical average at the time. That’s resulted in a full reservoir at Don Pedro, which currently holds 1,717,470-acre feet of water with an elevation of 804.3 feet.
While February’s totals were impressive, perhaps the most surprising month of the water year was May. On the heels of one of California’s wettest winters in years — thanks largely to the month of February — a storm of epic proportions rolled into the area and brought cold weather along with ample rainfall.
The cooler weather system resulted in what can only be described as winter in May, dropping to freezing levels and lowering the total amount of runoff from the large snowpack into Don Pedro Reservoir.
While the state did recover well from years of drought thanks to the ample water year, there were a few months that received less-than-average rainfall, including September (.45 inches below average) October (1.4 inches below average), December (3.6 inches below average) and April (1.96 inches below average). June and July received nearly zero inches of rainfall, which isn’t much less than the average, and there were zero inches of precipitation in August.
The 2020 water year began Sept. 1, and so far, just .28 inches of rainfall has landed in the region. This isn’t much less than the historical average of .57 inches for the month of September, which Cramer believes could be met soon as about .2 inches of rainfall is expected in the next week.