DENT IN DROUGHT
Rains ease fire concerns, start refilling reservoirs
The deluge of rain this week is helping to prime droughtstricken Marin County to begin refilling its ominously low water supplies and is giving local fire crews a sigh of relief.
“All of us are sleeping a little better now with this rain,” Marin County fire Chief Jason Weber said. “It was a busy summer.”
While encouraged by the downpours so far, local water agencies say the county will need significantly more rainfall in the coming months to make up for two years of dry conditions, which have resulted in a critical water shortage and the possibility of depleting local supplies.
“It’s a small step in the right direction and we’re really hopeful for more,” said Marin Municipal Water District communications manager Emma Detwiler. “Four inches of rainfall does not directly translate into 4 inches of reservoir levels rising.
It’s a bit of a different process than that.”
More than a foot of rain is expected to fall on Mount Tamalpais between Oct. 17 through Monday, according to the National Weather Service. More than 10 inches of rain had already fallen on the mountain as of Friday afternoon with another 4 to 6 inches expected to arrive when an atmospheric river passes through the region on Sunday and Monday.
In San Rafael, nearly 3 inches of rain was recorded as of Friday, which is about 157% higher than would normally be seen by the end of October, according to National Weather Service meteorologist Ryan Walbrun.
Similar trends are expected in surrounding areas such as Larkspur and Kentfield, which have also received several inches of rainfall this past week. Another 2 to 3 inches of rain is expected to fall in these areas through Monday, Walbrun said.
The rain is welcome news to the Marin Municipal Water District, which is facing the potential
of depleting its reservoirs by next summer in the event of another dry winter.
The district’s seven reservoirs in the Mount Tamalpais watershed, which make up 75% of its water supply, rely entirely on rainfall runoff. The reservoirs
are now less than a third full after two consecutive dry winters, including the second-driest water year in 143 years of records in 2020-2021.
Should this winter be similarly dry, the agency is consid
ering emergency drought projects to prevent from running out of local supplies, including building an up to $90 million, 8-mile pipeline across the Richmond-San Rafael Bridge to pump in Sacramento Valley water.
So far, the district has recorded more than 4 inches of rain at its Kent Lake reservoir as of mid-afternoon Friday, which is about 172% of its average by this time of year, according to Detwiler.
The rain was enough to soak the parched soils and ground to generate about 1,000 acre-feet of runoff into the district’s seven reservoirs, or just over 1% of the reservoirs’ nearly 79,600 acre-feet maximum capacity.
“We are seeing runoff generated; a small amount but we’re thankful for anything we can get right now,” Detwiler said.
After two dry winters in a row, California will need about 140% of its average rainfall this winter in order to generate normal runoff.
For MMWD, that 140% would equate to about 73 inches of rain, according to district water quality manager Lucy Croy. Should that occur, that could refill the district’s reservoir to close to 75% capacity or nearly 60,000 acre-feet. The reservoirs currently have about 26,000 acre-feet of supply.
That amount of rainfall isn’t unheard of. In the past 20 years, the district has recorded at least 73 inches of rain in three water years: 2006, 2017 and 2019, according to Croy.
For comparison, the district recorded just over 20 inches of rain this past winter, which is about 38% of normal.
The state figure is just a blanket projection, Detwiler said, with the runoff largely depending on the frequency and intensity of rainfall in the coming five to six months, Detwiler said.
The North Marin Water District’s only reservoir at Stafford Lake outside of Novato had yet to see enough rain to generate runoff. The lake provides about 25% of the district’s water supply for its 60,000 Novato customers, with the remaining 75% coming from the Russian River.
“We typically need about 7 to 8 inches of rainfall to saturate the soils within the Stafford Lake watershed before we get any runoff,” McIntyre said. “Rainfall through Thursday was 1.2 inches.”
On the fire risk front, Weber said the rains will allow local fire crews to transition crews to removing fire fuels throughout the county.
“It’s been years since we’ve been able to relax our guard in October because historically we haven’t had really significant rainfall until almost December,” Weber said.
Much of the year was focused on providing aid for significant blazes throughout the state, such as the Dixie fire, while also snuffing out blazes that occurred in Marin. There is still a chance fire crews will be needed in southern California, which is facing the possibility of a dry winter because of predicted La Nina weather patterns, Weber said.
While the rain is welcome, Weber warned that the years of protracted drought and its impacts on fire fuels will be an issue for years unless the state receives more consistent rainfall in the coming years.