Reservoir Operators React to Uncertainty in Snowmelt Runoff Forecasts

Abstract

Over 1 billion people rely on snow and ice for their water supply, and in many areas, reservoirs store the water after the snow melts. Deciding when to release water depends partly on forecasts of how much more rain and snowmelt will flow into the reservoirs. Often these forecasts express uncertainty, reporting a range of possible flows. We examined how those responsible for releasing water from reservoirs respond to forecasts using a case study of the historical record of past forecasts and water releases in California's Sierra Nevada. Results from a panel data model with fixed effects showed that these water managers hedge their bets against the possibility of less water than forecasted. Greater uncertainty in a forecast was associated significantly with a reduced amount of released water, and the effect of uncertainty on releases declined as the forecast volume increased (adjusted R 2 ¼ 0.70, F-test p ≪ 0.001). Our results suggest that increasing water managers' confidence in upcoming flows by reducing forecast uncertainty would allow more water to be released from reservoirs earlier in the year, without the need for direct coordination with these managers.

Flooding and the interannual variability of hydrologic quantities in the Missouri River basin

“…It has long ago been recognized that, because societal and environmental needs change over time and because of the changing global climate, it is necessary to periodically review and adjust reservoir operating rules (Higgins & Brock, 1999; Hotchkiss et al, 2000). Reservoir release operations are guided by state‐of‐the‐art hydrologic forecasts to achieve water management objectives (Stillinger et al, 2021; Turner et al, 2020). But there remains a gap in the application of climate data for reservoir flood control (Mishra et al, 2022).…”