Although the amount of precipitation experienced by the region for the month surpasses the historical average rainfall amount for May, it still is not enough to combat the severe drought plaguing the state.
According to Turlock Irrigation District utility analyst Jason Carkeet, the Tuolumne River Watershed has experienced 1.80 inches of precipitation for May as of Tuesday, which is 0.19 inches above the historical average for this month.
However, Carkeet revealed that the region is still going to need a lot more rain if it wants to come close to meeting the historical precipitation average.
“When a year’s average amount of watershed precipitation is just over 36 inches, the 1.80 inches to date for May is not a significant contribution overall,” said Carkeet. “It helps, but it is not enough to significantly change the circumstances.”
According to Carkeet, what TID considers an average year does not depend on the amount of precipitation the city receives, rather the deciding factor lies in the amount of accumulated runoff, or precipitation that is either not evaporated or absorbed into the ground.
Carkeet reported that due to conditions caused by the recent string of dry years, the Tuolumne River Watershed would need at least 42 inches of rainfall over the course of one year in order to get into the range of precipitation that would yield average runoff, which is approximately 1,955,000 acre-feet.
Since the year has gotten off to a historically dry start, the amount of accumulated precipitation for the Tuolumne River Watershed from Sept. 1 to May 26 is at 19.30 inches, or 54.7 percent of average amount of precipitation expected for that time frame.
If the region hopes to meet the average amount of precipitation needed to accumulate 1,955,000 acre-feet of runoff, it would need at least another 22.7 inches of rainfall in June, July and August—an amount nothing short of a miracle to achieve.
“Our precipitation records, which go back to 1931, show no record of a June through August precipitation yield anywhere close to that,” said Carkeet. “Average yield for June through August is 0.89 inches.”