The idea of being “average” has likely never sounded so good to the Turlock Irrigation District following a report unveiled this week by the California Department of Water Resources that forecasted the region could potentially experience 2,010,000 acre feet of runoff in an average scenario this year, a total that is 103 percent of the historical amount.
This report is called Bulletin 120, which is a publication that is issued by the DWR four times a year in the second week of February, March, April and May. The report contains forecasts of the volume of seasonal runoff from the state’s major watersheds, as well as summaries of precipitation, snowpack, reservoir storage and runoff in various regions of California.
In the February forecast, the average scenario for the region shows approximately 2,010,000 acre feet in unimpaired runoff, which is approximately 103 percent of the historical 1,955,000 acre feet average. Unimpaired runoff represents the natural water production of a river basin, unaltered by upstream diversions, storage, or by export or import of water to or from other watersheds.
TID Utility Analyst Jason Carkeet said with Bulletin 120 the DWR considers snow course measurements, or snow surveys, which measure the water content of snow at the first of the month, the precipitation to date in terms of inches equivalent of rainfall, runoff to date and other parameters before they come out with a forecast for prospective runoff with 80 percent probability range that the actual value will fall within the upper and lower limits.
For the region, the 80 percent probability range is between a lower limit of 1,430,000 acre feet of runoff and an upper limit of 2,970,000 acre feet of runoff.
“I would say that the B120 values were within the ranges we were expecting based on some of our other analyses,” said Carkeet.
In his weekly water report, Carkeet revealed that the Tuolumne River Watershed accumulated 9.40 inches of precipitation in the month of January, which he said is approximately 150 percent of the historical average of 6.32 percent.
This marks the fourth consecutive month that actual rainfall amounts have exceeded their monthly historical averages since the precipitation year started in September. Data up until Feb. 7 showed that the Tuolumne River Watershed has experienced 26.42 inches of rainfall, which is 128.3 percent of average for this date.
“We have a good start to the water year. However, the precipitation forecasts for the next 16 days are for somewhat dry conditions for this time of year,” said Carkeet. “We will need to have wetter-than-average precipitation conditions through spring in order to start approaching runoff conditions that may fill Don Pedro.”
TID will host its 2016 Irrigation Season Operations Meeting at 5:30 p.m. on Tuesday in the TID Boardroom, 333 E. Canal Dr. During this meeting, information will be presented on currently hydrology and 2016 irrigation season operations.