Forecast Informed Reservoir Operations

FIRO is a reservoir-operations strategy that better informs decisions to retain or release water by integrating additional flexibility in operation policies and rules with enhanced monitoring and improved weather and water forecasts (American Meteorological Society; 2020). Since 2014, CW3E and federal, state, and local partners have developed, tested, and implemented FIRO at reservoirs across the Western United States. FIRO is now being assessed nationwide.

What is FIRO?

Water resources are increasingly stressed by growing demand, more frequent swings between flood and drought, and declining water supply reliability. FIRO offers a way to get more out of the infrastructure that already exists, using better forecasts to improve both water supply and flood protection, without pouring any new concrete.  

When construction of dams and reservoirs in the U.S. peaked in the 1960s, weather forecasting was not advanced enough to reliably predict rainfall, runoff, and drought. As a result, reservoir operating rules were developed based on historical observations and conservative flood management practices. These operating rules are still widely used today.

However, forecasting science has advanced significantly since then. CW3E has been at the forefront of many of these advances, developing improved atmospheric river forecasting, hydrologic modeling, observational tools, and forecast verification methods that now give reservoir operators far more information about incoming storms, potential watershed response, and periods of dry weather and drought. FIRO incorporates these improved forecasts into reservoir decision-making, providing an additional, cutting-edge tool to help inform storage elevations and release timing. When dry conditions are forecast, operators can store more water to buffer against drought; when storms are expected, they can release water ahead of time to make room for large inflows. In practice, FIRO projects, such as the one in the Russian River Watershed, are demonstrating significant water supply and environmental flow benefits, while maintaining, and in some cases increasing, flood risk management.

A conceptual illustration of how FIRO works around a storm. — Figure 1. A conceptual illustration of how FIRO works before and after a storm. Using weather and water forecasts, operators release water ahead of an incoming storm to make room for inflows, then refill the reservoir when it is safe to do so. This can leave storage above the conventional storage limit after the event, increasing water supply without compromising flood protection.
Adapted from F. M. Ralph, 1 May 2024.

FIRO is a Research And Operations Partnership (RAOP), an iterative approach that allows advances in forecasting science to be evaluated, tested, and applied in real-world operations. Collaboratively developed by partners across federal, state, and local agencies and universities, FIRO integrates atmospheric science, hydrology, water resource engineering, and environmental science. This ongoing feedback between innovation and application helps improve forecasting capabilities over time while ensuring that new tools are practical, effective, and responsive to operational needs.

The FIRO Process

COLLABORATION

Reservoir operators, researchers, water managers, and community and agency partners align around a shared mission to improve reservoir operations at a specific site. Steering Committees establish objectives, coordinate technical work, drive progress, and ensure diverse expertise and perspectives are represented during the FIRO process. Through relationship and trust-building, the Steering Committee ensures alignment essential to FIRO’s success.

EVALUATION

Technical work teams, composed of experts from diverse fields, assess whether FIRO may provide operational benefits by analyzing meteorology, hydrology, forecast skill, watershed conditions, operational constraints, and other site-specific factors. Assessments of hydrometeorological forecast skill and potential FIRO alternatives are modeled against historical operations, and the results are documented in a Viability Assessment that identifies alternatives for future operational testing. Dependent on the project, an initial preliminary viability assessment will precede a more refined final viability assessment.

TEMPORARY IMPLEMENTATION

Guided by the findings of the Viability Assessment, the Steering Committee can submit a formal request to USACE for a temporary change to the reservoir’s existing water control plan by following the water control plan deviation process. These deviations, typically lasting from one to five years, provide critical operational testing grounds that gather real-world data and help show FIRO applicability and efficacy. This temporary operational bridge aims to demonstrate improved performance in flood risk management, water supply reliability, and environmental benefits, laying the groundwork for a permanent change to reservoir operations through a water control manual update.

PERMANENT IMPLEMENTATION

While the FIRO process is separate from the formal Water Control Manual update process, it can support updates by leveraging the research and understanding gained from viability assessments. If incorporated into a U.S. Army Corps of Engineers Water Control Manual, FIRO then becomes part of the reservoir’s authorized operating rules.

Figure 2. The FIRO process moves through evaluation, implementation, and potential authorization, with collaboration among partners ongoing throughout. Each step builds on the last, from forming a Steering Committee to a potential update of the reservoir’s Water Control Manual. Not every project completes every step, and timelines vary by site.