The Brazilian interconnected power system consists of a set of over 150 medium and large hydropower plants, and is complemented by a large set of small hydropower plants, and thermal and wind power plants. Hydropower plants are operated to meet most of the energy demand, while the complementary system is dispatched to make up the shortage in supply. During 13 years from 2000 to 2012 on average 91% of Brazilian effective electric generation was provided by hydropower. However, in the last three years this percentage was reduced, in sequence, to 79, 73, and 71%. Intense and expensive thermal dispatch was necessary, while hydropower production was reduced and reservoir storages were drawn down. In the last three years, several major watersheds in Brazil have experienced a very severe drought. At the same time, the energy problem was exacerbated by demand increase and delayed expansion of the power system. To analyze the impacts of drought on the hydropower system, we propose to focus not only on the inflows but also on energy. Three variables were compared: historical reservoir inflows from 1930 to 2015, corresponding energy inflows, and optimal hydropower production. A nonlinear programming model, called HIDROTERM, previously developed for the hydrothermal system, was used to evaluate the optimal hydropower production under the historical inflows. We analyzed the intensity and duration of the historical droughts and evaluated the impacts of the most recent 2012-2015 severe drought on the Brazilian hydropower system.
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