Hydroelectricity is generally considered to be a reliable method of generating electricity.
Operators of hydroelectricity facilities that are designed to be flexible can control their electrical output by choosing how much water to allow through the intakes. As long as there is plenty of water in the reservoir, operators can plan in advance how much electricity the dam will generate.
An extended drought could affect the reliability of a hydroelectric dam by reducing the amount of water in the reservoir. Droughts and floods can also affect the reliability of smaller, run-of-river installations, as their electrical output depends on the available volume of water and the rate at which it flows past the turbine.
Large-scale hydroelectric power stations in the UK generate reliable and predictable electricity, using proven and efficient technology. This means they can balance the output of more intermittent energy sources. The flexibility of hydroelectricity means it can be used very quickly, and can easily be brought online to generate extra electricity when demand increases.