By Ashlee Casey, Executive Director, Water Forum
This summer, water managers across the Sacramento region were watching Folsom Reservoir closely. Early projections suggested summer operations might leave storage below the Water Forum’s 300,000-acre-foot (AF) end-of-December planning minimum, raising concerns about how the region would fare if the coming winter was dry. The planning minimum provides a safeguard for protecting regional water supplies and the health of the lower American River heading into a potentially dry year.
Fortunately, conditions have improved. Folsom Reservoir ended the 2026 water year on September 30 with 444,000 AF in storage and is on track to stay above the 300,000 AF planning threshold through the end of the calendar year. The stronger-than-expected storage provides a cushion for regional water supplies and the lower American River in the months ahead, even as a very strong El Niño increases the likelihood of a wetter-than-average winter.
A small reservoir with a big job
Folsom Reservoir plays an outsized role for the Sacramento region and the statewide water system. Although relatively small (its maximum capacity is 966,000 AF), it is part of the much larger federal Central Valley Project (CVP), operated by the U.S. Bureau of Reclamation, that includes 20 dams and reservoirs with nearly 12 million AF of total storage. Because of that broader role, Reclamation must balance many priorities when deciding how much water to store or release from Folsom, including local and regional water supply, environmental requirements, flood management, Sacramento–San Joaquin Delta (Delta) water quality, and other needs across the state.
Folsom Reservoir’s location on the American River and proximity to the Delta also makes it one of the quickest tools Reclamation can use to help maintain water quality in the Delta. When extra freshwater is needed to keep salinity in check, Folsom often plays a key role.
A stronger outlook for a wet winter
This year’s El Niño is already very strong and may reach historic levels. Recent forecasts point to an increased likelihood of a wetter-than-average winter across California, including the Sacramento region. Climate scientist Daniel Swain’s recent analysis identifies Sacramento as part of a region with particularly high confidence in a wet winter and notes an elevated likelihood of extremely wet conditions.
The forecast gives water managers a clearer signal to prepare for wet weather. The amount, timing and location of rain and snow remain uncertain, however, as does what those conditions will mean for runoff into Folsom Reservoir.
Careful management of end-of-year storage remains important across a range of conditions. If the winter is drier than expected, water held in Folsom helps protect regional supplies and the lower American River. If major storms arrive, Reclamation will need to release water to make room for incoming runoff and manage flood risk.
El Niño may also influence operations in another way, beyond precipitation alone. Warm ocean conditions are contributing to massive, slow-moving planetary waves (Kelvin waves) that could temporarily raise coastal sea levels along our coastline by about six inches. Higher ocean levels can push more saltwater toward the Delta. If that happens, Reclamation may need to release more water from Folsom because flows from Folsom reach the Delta faster than flows from other CVP reservoirs.
These factors highlight both the value of entering the winter with a minimum of 300,00 AF in storage and the complexity of managing Folsom Reservoir as conditions shift.
Preparing for greater variability
Climate change is making reservoir operations more challenging. Water Forum 2050 planning anticipates a future with less snowpack, earlier snowmelt, more extreme precipitation and a greater likelihood of critically low storage at Folsom Reservoir.
Those changing conditions make the relationship between the Water Forum and Reclamation increasingly important. Reclamation operates Folsom Reservoir as part of a larger federal water system, while its decisions have direct consequences for Sacramento-area water supplies and the lower American River. Continued coordination ensures that regional science, water supply needs, and environmental priorities inform those decisions.
The new Water Forum 2050 Agreement provides a framework for adapting to changing conditions while continuing to pursue the Water Forum’s coequal objectives of a safe, reliable water supply and a healthy lower American River. Through the American River Climate Adaptation Program, or ARCAP, Water Forum members will evaluate and advance actions that can provide additional flexibility during critically dry periods, including conservation, groundwater recharge and banking, reservoir operations and regional infrastructure.
Forecasts point toward a wetter-than-average winter, while the timing and amount of precipitation remain uncertain. Entering the winter with a minimum of 300,00 AF in Folsom gives the region a stronger starting point as water managers prepare for the months ahead. Building and maintaining that flexibility is central to how the Water Forum is preparing for a more variable future.