With a dry winter like this year and last, we end up getting a lot of questions at Sonoma Ecology Center about the health of our watershed. We’ve heard from many community members wanting to know about current water supply levels, what to expect in the months to come, and what implications drought years might have on the environment and our daily lives. With all this in mind, we turned to our Senior Scientist and Research Program Manager, Steven Lee, to help answer your pressing questions about the drought.
Where are we with rainfall and water supply right now, and how does it compare to what we experienced last year? “We all remember that we had a really low rainfall year last year,” says Lee, “Our creeks were completely dry all the way up from the tidelands in the lower watershed up through the Kenwood area.” Except for some small pools where some fish and other aquatic species were able to wait for rain and steady streamflow, creek beds were the driest Lee has seen in his many decades here in Sonoma Valley. This was especially troubling for all species who rely on the creek to live or rely on it as a source for drinking water. “We were all pretty concerned about what the next year would hold for us, and what the next rainy season would look like,” Lee added.
Sonoma Creek at it’s driest levels during the drought prior to the first rains of the season and at flood stage levels on October 24th, 2021
On October 24th, 2021 Sonoma County experienced a record breaking storm that brought the creek up to flood stage levels and brought more rain to Sonoma Valley in 24 hours than the area had seen in the entire year prior. This extreme weather event brought a close to fire season and alleviated some of our drought concerns, especially as rainfall continued to be consistent through much of November and December. That regular precipitation through early winter resulted in significant snowpack in the Sierra Nevada. This brought statewide snowpack to 160% of average by the end of December 2021, and that snowpack supplies 30% of the state’s water needs.
While this is reassuring news for the state at large, Sonoma County does not receive its water from the Sierra snowpack. We rely on rainwater stored as groundwater or in reservoirs, including Lake Sonoma (our largest reservoir), and Lake Mendocino (which is partially supplied by an intertie to the Eel River fed by Lake Pillsbury). Releases from Lake Sonoma and Lake Mendocino to the Russian River provide water used by Sonoma Water’s aqueduct to supply most of the North Bay’s urban water users.
Why did the weather dry up in early 2022? Common to La Nina weather patterns, explains Lee, here on the West Coast, a high pressure ridge has been blocking storms from their normal path, and moving them north, toward Washington and British Columbia in Canada. This high pressure ridge has persisted all through January and February, turning what is typically the West’s wettest time of the year into the record breaking driest January in state history.
A high pressure system along the West Coast has been preventing weather systems from moving in for most of January and February resulting in a record breaking few dry months for the West.
“To give a sense of where that leaves us historically, we can look at rainfall over the last decade to see that there are years where Sonoma has experienced very low rainfall, the most recent being last year and 2015,” says Lee. “If we look back a few decades, we can see that our lowest recorded rainfall year prior to 2020 is 1977, when Sonoma County only averaged 11 inches of rain.”
Rainfall in Sonoma Valley varies, from about 20 inches on average near the bay, to over 50 inches along northern ridgetops. Over all of Sonoma Valley, average annual rainfall is about 35 inches. Last season, Sonoma Valley had its lowest average precipitation on record.
Lee explains, “In comparison to earlier drought years like 1977, we’re now seeing a measurable overall decline in groundwater levels. There is a relationship between low groundwater levels to stream flow, explaining why we also had the worst recorded stream flow for Sonoma Creek last year. So, not very good conditions in the 2020-2021 water year.”
The above graph depicts rainfall for the past seven decades in Sonoma Valley.
However, our water year is not over yet. A water year is measured from October 1st to September 30th of each year. “This year we’ve had a little bit of a rebound in comparison to what we had last year,” says Lee, highlighting the fact that in Glen Ellen on October 24th 2021 the area received more rainfall in one 24 hour period than was received all of the prior water year. “So things are looking a little bit better, but with no rain since December, there is cause for concern.”
The above graph, courtesy of Sonoma Water, depicts our current water supply levels in Lake Sonoma.
What does the drought mean for our current water supply levels? If you look at the lake water levels for the last ten years in our largest reservoir, Lake Sonoma, it’s visible that in a normal year the water levels rise with the rainy season and then trail off into the dry season. Lee explains, pointing to the graph, “you can track the water levels and see that we have had some great years in the past, like 2019 where we had a good year with high rainfall throughout October to March. We already had good lake levels in 2018, so it didn’t take much to fill it back up again.” But with consecutive dry years one after another, like Sonoma is experiencing right now, it takes more and more to refill Lake Sonoma. “So we’ve started off this year quite low,” says Lee, “and with that big rainstorm in October and the wet months we did get, we only got back to water levels that we were at this time last year.”
The reality of the situation is that we are no better off nor worse, when it comes exclusively to water storage, than we were last year. Looking ahead indicates that we are looking at similar predictions to last year as to what to expect this summer for water use restrictions. We can expect a similar experience as well when it comes to overall drought conditions. Moreover, there are implications for the environment and for flora and fauna as they live through multiple drought years.
As we prepare for what will likely be a dry year ahead there are a variety of steps that we can take to support our watershed, our local wildlife, and ourselves. From saving water when we shower, to watering gardens in the early morning or at night, or even planning to install a water catchment system on your property, SEC is here to support you in exploring ways to be resilient through a changing climate.
Stay informed and sign up for our newsletter or follow us on social media as we share through the dry season our recommendations to care for our shared experience of drought and what solutions are possible. One of our key recommendations for building drought resiliency is slowing, sinking, and storing rainwater when it is bountiful. Read more at the below link and stay informed!
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