Abstract
Standard impoundment operation rules (SIOR) are pre-defined guidelines for refilling reservoirs before the end of the wet season. The advancement and availability of the seasonal flow forecasts provide the opportunity for reservoir operators to use flexible and early impoundment operation rules (EIOR). These flexible impoundment rules can significantly improve water conservation, particularly during dry years. In this study, we investigate the potential application of seasonal streamflow forecasts for employing EIOR in the upper Yangtze River basin. We first define thresholds to determine the streamflow condition in September, which is an important period for decision-making in the basin, and then select the most suitable impoundment operation rules accordingly. The thresholds are used in a simulation–optimization model to evaluate different scenarios for EIOR and SIOR by multiple objectives. We measure the skill of the GloFAS-Seasonal forecast, an operational global seasonal river flow forecasting system, to predict streamflow condition according to the selected thresholds. The results show that: (1) the 20th and 30th percentiles of the historical September flow are suitable thresholds for evaluating the possibility of employing EIOR; (2) compared to climatological forecasts, GloFAS-Seasonal forecasts are skillful for predicting the streamflow condition according to the selected 20th and 30th percentile thresholds; and (3) during dry years, EIOR could improve the fullness storage rate by 5.63% and the annual average hydropower generation by 4.02%, without increasing the risk of flooding. GloFAS-Seasonal forecasts and early reservoir impoundment have the potential to enhance hydropower generation and water utilization.
Highlights
The rapid population and economic growth in recent decades, along with climate change and variability, impose more stress on water resources and cascade reservoir systems
As the first step of our evaluation, we select thresholds to evaluate the streamflow condition for impoundment operation
Results show that for GloFAS-Seasonal reforecasts below 20%, the ROC skill score (ROCSS) exhibit a decline in skill evaluation
Summary
The rapid population and economic growth in recent decades, along with climate change and variability, impose more stress on water resources and cascade reservoir systems. Water managers and stakeholders employ predefined impoundment rules for reservoir systems These fixed rules, so-called standard impoundment operation rules (SIOR), are derived based on the historical flow records [7,9,18]. The SIOR is designed to reduce the flood control risk during the impoundment period These fixed rules are unable to fully replenish the storage of the reservoir during dry years, which could lead to water shortage. We investigate different streamflow thresholds to evaluate the possibility of employing EIOR These thresholds can be considered as an indicator for the dry condition which has adverse effects on reservoir impoundment operation. We apply these thresholds to evaluate the skill of the GloFAS-Seasonal streamflow forecast for selecting EIOR or SIOR.
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