Rainfall patterns are a determinant factor for annual changes in hydroelectricity production. Despite the low total growth rate anticipated up to 2020 at the EU level, the importance of hydropower may increase (EEA 2017). Hydropower reservoirs can provide energy storage and load balancing functions, contributing to the flexibility necessary to integrate high levels of renewable energy from intermittent sources.

Regulation has the purpose to save water, and thus energy, to use it when needed. The idea is to maximize the production of energy during periods when the demand is the highest and benefits as well.

To be able to accommodate spring floods, the lowering of reservoirs during winter has to be adapted to the expected volume of this spring flood. However, at the same time, reservoir operators intend to keep reservoirs at maximum levels over the summer to guarantee the maximum possible energy production. Accurate hydrometeorological forecasts provide useful information for reservoir managers that can avoid important economic losses to hydropower generators. The aim of S2S4E is to investigate to which extent these improved forecasts can optimise hydropower production.