Joint and respective effects of long- and short-term forecast uncertainties on reservoir operations

•A novel statistical method for analysis of forecast-based reservoir operation.•Partition of joint effects of long- and short-term forecast uncertainties.•Diagnosis of respective effects of long- and short-term forecast uncertainties.

SummaryForecast uncertainties are a major problem in forecast-based water resource management. This study aims to improve the combined use of long- and short-term streamflow forecasts in reservoir operations by investigating the joint and respective effects of long- and short-term forecast uncertainties on decision-making processes. Forecast uncertainties in ensemble streamflow forecasts are explained, and the joint effect is characterized by a matrix of operation decisions. A novel statistical partitioning method is developed to diagnose the respective effects of long- and short-term forecast uncertainties, particularly on an experimental operation of the Danjiangkou Reservoir in China. Given the large regulating capacity of this reservoir, long-term forecast uncertainties inevitably surround its release decisions. When a fixed carried-over storage is used to couple long- and short-term forecasts, an ending storage effect is observed. As a stage approaches its end, the release decision becomes increasingly dependent on the carried-over storage, thereby increasing uncertainty in decision-making as a result of long-term forecast uncertainty. This finding highlights the importance of developing reliable long-term forecasts and selecting a proper carried-over storage to aid the decision-making process. This study proposes a sliding carried-over storage strategy to circumvent the ending storage effect. Results show that, using the same long-term forecast, the proposed strategy significantly alleviates the ending storage effect and reduces uncertainties in the decision-making process. The sliding carried-over storage strategy provides an efficient approach to the combined use of long- and short-term forecasts and improves reservoir operations.