Average domination: A new multi-objective value metric applied to assess the benefits of forecasts in reservoir operations under different flood design levels

Worldwide, reservoirs are used to buffer against both extreme floods and extreme droughts. However, operations favoring each of these and other management objectives conflict. Fortunately, tradeoffs in operations can often be mitigated by using hydrologic forecasts to condition release decisions, and significant research has investigated the value of using forecasts for this purpose. However, these studies have struggled with how to quantify forecast value in multi-objective contexts where the benefits may accrue unevenly to different objectives that stakeholders value differently. To address this research gap, we introduce a new metric for quantifying forecast value on multi-objective problems: the average improvement on each objective when moving from a solution that does not use forecast information (a baseline solution) to solutions that do use forecast information and outperform the baseline solution on all objectives. We call this metric "average domination"and use it to investigate whether and how the value of forecast information for multi-objective reservoir operations changes with different flood protection constraints, using the Red River Basin in Vietnam as an example. To assess this, we design multi-objective operations at four reservoirs in the basin both with and without forecast information conditioning release decisions under constraints that the operations ensure protection to downstream water levels with either 100-year or 500-year return levels. Based on the average domination metric, we find that in the Red River Basin, the value of forecast information for all objectives is the same or greater under the more severe 500-year flood design requirement. These findings, identified by our new metric, illustrate that it can be especially beneficial to condition operations on forecast information when stakeholders strongly favor higher levels of risk aversion for flood protection.