Abstract
Abstract. Considerable research effort has recently been directed at improving and operationalising ensemble seasonal streamflow forecasts. Whilst this creates new opportunities for improving the performance of water resources systems, there may also be associated risks. Here, we explore these potential risks by examining the sensitivity of forecast value (improvement in system performance brought about by adopting forecasts) to changes in the forecast skill for a range of hypothetical reservoir designs with contrasting operating objectives. Forecast-informed operations are simulated using rolling horizon, adaptive control and then benchmarked against optimised control rules to assess performance improvements. Results show that there exists a strong relationship between forecast skill and value for systems operated to maintain a target water level. But this relationship breaks down when the reservoir is operated to satisfy a target demand for water; good forecast accuracy does not necessarily translate into performance improvement. We show that the primary cause of this behaviour is the buffering role played by storage in water supply reservoirs, which renders the forecast superfluous for long periods of the operation. System performance depends primarily on forecast accuracy when critical decisions are made – namely during severe drought. As it is not possible to know in advance if a forecast will perform well at such moments, we advocate measuring the consistency of forecast performance, through bootstrap resampling, to indicate potential usefulness in storage operations. Our results highlight the need for sensitivity assessment in value-of-forecast studies involving reservoirs with supply objectives.
Highlights
Coupled natural-engineered water resources systems provide a multitude of services to society
Taking Burrinjuck (Fig. 5a) as an example, we find that an injected forecast error of 0.2 could result in cost reductions anywhere from −5 to +40 % for the supply objective
Tential to reduce the instances of supply failure and to extend the life of existing infrastructure at very little cost; forecast systems are very cheap compared to developing new supply infrastructure
Summary
Coupled natural-engineered water resources systems provide a multitude of services to society. A properly functioning system can ensure reliable public water supply, support agricultural and industrial activity, produce clean hydroelectricity, provide amenity, sustain ecosystems and protect communities against damaging floods These benefits are by no means guaranteed; the performance of a given system depends on the quality of its operating scheme and the intelligence used to support management decisions on the storage, release and transfer of water. The operator might select from a predefined lookup table the desired volume of water to release from a reservoir based on the time of year, volume of water held in storage and current catchment conditions (soil moisture, snowpack, etc.) The problem with this approach is that the decisions it recommends are optimal only under the narrow range of historical forcing conditions upon which they are trained. Results provide new insights into the risks operators take when applying seasonal forecasts to critical management decisions in systems dominated by a supply objective
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