On December 1st, the Department of Water Resources (DWR) announced an initial State Water Project (SWP) allocation of 10 percent of requested supplies for the new water year (compared to last year’s initial allocation of 5%). This allocation represents the first water supply forecast of the season for the 29 public water agencies served by the SWP which provides water to 27 million Californians and 750,000 acres of farmland.
The SWP is contractually required to make an initial allocation forecast by December 1 each year. Since it is so early in the season, the initial allocation typically reflects current hydrological conditions, existing reservoir storage, and an assumption of dry conditions through the rest of the year. So far, the wet season is off to a good start with beneficial rain falling in Northern California and Southern California already seeing significant rainfall following a dry year last year.
“Recent history has shown us that anything can happen during a California winter, so it’s important that our early season allocation for the State Water Project is conservative,” said DWR Director Karla Nemeth. “Traditionally our wettest months are yet to come. With improvements to forecasting and science, we are better prepared to capture water supply during wet periods if Mother Nature delivers.”
Across the state, California’s water supply starts the season in good shape with statewide reservoir storage just above average at 114 percent. Lake Oroville, the SWP’s largest reservoir, is at 100 percent of average for this time of year, slightly above where it was at last December.
Last year, the SWP’s initial allocation began at five percent and increased to 50 percent by the end of the season. As winter progresses, if the state sees an increase in rain and snowfall totals, the allocation forecast may increase as well.
Each year, DWR provides the initial SWP allocation based on available water storage, projected water supply and water demands. Allocations are updated monthly as snowpack, rainfall and runoff data is analyzed, with a final allocation typically determined near the end of the season in May or June.
Historical data on SWP allocations is available at https://water.ca.gov/programs/state-water-project/management/swp-water-contractors.
