DWR Activates FIRO Operations at Lake Mendocino Ahead of AR Sequence ​

The Department of Water Resources has activated Forecast Informed Reservoir Operations (FIRO) protocols at Lake Mendocino ahead of a predicted sequence of three atmospheric rivers expected to make landfall along the Northern California coast over the next 10 days. In plain English: instead of managing the reservoir like it's 1955, they're using modern weather forecasting to make smarter decisions about when to store water and when to release it.

FIRO represents what happens when hydrologists and meteorologists actually talk to each other — a revolutionary concept that took several decades of the two disciplines politely ignoring one another to achieve. The traditional approach to flood control reservoirs is elegantly simple: keep the pool low in winter to catch floods, fill it up in spring. The problem is this wastes enormous amounts of water that gets released pre-emptively "just in case" a storm comes. FIRO uses 72-hour precipitation forecasts and ensemble modeling to thread the needle between flood protection and water supply.

What's Coming ​

The AR sequence is rated AR3 to AR4 on the Ralph scale — strong enough to produce significant rainfall (4-8 inches in the Russian River watershed) but not the "duck and cover" AR5 category. The FIRO protocol allows operators to carry a higher pool level than the static flood control manual would permit, banking on forecast confidence that the worst of the precipitation will be manageable within the remaining flood pool space.

If the forecasts are right, Lake Mendocino could capture an additional 8,000 acre-feet of water that would otherwise have been pre-released — enough to supply roughly 24,000 households for a year. If the forecasts are wrong and the storm is bigger than expected, well, that's why the emergency spillway exists, and also why the Army Corps made DWR carry $500 million in liability insurance.

Track Record ​

Since FIRO was formally adopted at Lake Mendocino in 2020, the protocol has been activated 14 times. In 12 of those events, FIRO operations resulted in measurable water supply gains without compromising flood safety. In the remaining two, operators reverted to traditional rule curves when forecast uncertainty exceeded thresholds — which is the system working exactly as designed, even if it's slightly less exciting than "the algorithm nailed it every time."

FIRO is currently being evaluated for expansion to Lake Sonoma, Prado Dam, and New Bullards Bar Reservoir. The question is no longer whether forecast-informed operations work, but how many reservoirs can adopt them before someone has to update all the O&M manuals.