Close to Home: Saving rainwater for sunny days to come

New forecasting methods have resulted in savings of 28,000 acre-feet, about two -thirds of the North Bay’s annual demand.|

The current water year, which began Oct. 1, has been wetter than usual, with the Russian River watershed accumulating 119% of the yearly average rainfall, totaling 49.38 inches since October.

In the past, we might have celebrated our good fortune and watched lake levels rise only to watch much of it sent downriver to the Pacific Ocean as reservoirs reached an inflexible upper threshold. Today, we get to continue enjoying that ample rainfall long after summer sunshine arrives.

Grant Davis

With almost a decade of data under its belt, the Russian River Forecast-Informed Reservoir Operations program has been making great strides by demonstrating the viability of this strategy to operate reservoirs more effectively using modern technology and forecasting.

This year, we expect the new method to ensure an additional 19,000 acre-feet of water in the Lake Sonoma reservoir heading into the summer, just as it did last year, thanks to our ability to leverage weather forecasting techniques and adapt how we manage our reservoirs. Add to that another 9,000 acre-feet stored in Lake Mendocino. An acre-foot equates to 325,851 gallons.

That 28,000 acre-feet represents a substantial savings, or almost 65% of Sonoma Water’s annual demand, given that the agency is projecting its three-year average annual water sales to be just under 43,000 acre-feet.

This nationally recognized project involves several state and federal agencies, which in collaboration with Sonoma Water, performed an initial assessment at Lake Mendocino and are now assessing its viability at Lake Sonoma.

While wet years tend to replenish our surface level water supply more quickly, we have also seen improvements to the region’s aquifer water levels. Following the 2023 winter storms, groundwater levels began to recover, approaching 2019 levels. This is particularly significant considering the multiyear drought that led to historically low levels in Lake Sonoma and impacts on groundwater users in water-scarce areas across the county.

Building on the successful utilization of forecast-informed operations, we are actively pursuing efforts with federal policymakers to support funding and programming for improved sub-seasonal to seasonal precipitation forecasting. Sub-seasonal (two- to six-week) to seasonal (two- to 12-month) precipitation projections can enhance forecasting at longer lead times to help manage extremes of droughts and floods, and would provide actionable information that agricultural and urban water users can employ to support water project operations, drought preparedness and response and innovative water planning and management strategies.

While we hope for more winters with ample rainfall, we’ll continue harnessing innovative programs as we adapt to our changing climate to face future challenges with our best foot forward.

Grant Davis is general manager of Sonoma Water.

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