An electricity grid does a pretty good job of connecting reservoirs in the high mountains with distant cities and other loads. Granted there are some transmiss

An electricity grid does a pretty good job of connecting reservoirs in the high mountains with distant cities and other loads. Granted there are some transmission inefficiencies, but still far better overall efficiency than any heat engine can manage. Unpredictable rainfall (e.g. extended droughts brought on by climate change) is the biggest risk factor when hydroelectricity dominates a country's energy supply. New Zealand is a good example of this: in some winters there isn't enough storage in the lakes [due to a lack of rainfall] and wholesale electricity prices spike dramatically.