Flood water resources utilization in cascade reservoirs considering flood forecast information

Study region The lower Jinsha River reservoir group (Wudongde, Baihetan, Xiluodu and Xiangjiaba) and Three Gorges Reservoir, China. Study focus This study examines floodwater utilization in cascade reservoirs under forecast uncertainty. A framework estimates the upper bound of pre-fill volume (UBFV) from two-stage flood processes linking forecast-period information to subsequent flood characteristics. Forecast errors are incorporated into reservoir operation, with UBFV constrained by the expected maximum reservoir water level not exceeding a specified reference level. New hydrological insights for the region Forecast-period information is significantlycorrelated with subsequent flood characteristics (coefficients of at least 0.67), supporting conditional scenario generation but not independently establishingforecasting skill. Under the investigated 2020 flood conditions, UBFV ranges from 38 to 54 × 10⁸ m³ for Three Gorges and from 116 to 120 × 10⁸ m³ for the lower Jinsha cascade. Simulated flood-season hydropower generation increases by 1.45%–4.86%. For Three Gorges, the highest UBFV occurs at a five-day horizon under current forecast conditions; in the examined error scenarios, errors above approximately 10% can reduce UBFV as the horizon lengthens. The Jinsha cascade is less sensitive to forecast errors. Flood shape and duration also matter: the concentrated 1981 flood allows more pre-filling, whereas the prolonged 1998 basin-wide flood allows less. The findings inform case-specific dynamic flood-limited water-level control.