Brazil will keep its backup thermoelectric plants operating until at least 2015 as generation plummets from drought-parched hydropower dams, according to national grid operator ONS.

Speaking at an event in Rio de Janeiro, ONS general director Hermes Chipp warned that even above-average rainfall would not alleviate the country's reliance on oil and gas-fired thermal plants.

"The objective is... not to let the [water] level fall too low and to replenish the reservoirs," Chipp was quoted as saying by local news portal Jornal da Energia.

Brazil's electric power crisis has been heightened by the onset of the dry season, which spans from May to December.

ONS predicts that dam levels in the country's southeast and midwest will fall from 33% in July to 19% in November.

According to the latest data from Brazil's energy trade chamber CCEE, thermoelectric generation rose 21% year-on-year in May to 17.3 average GW.

Hydropower generation over the same period dipped 5% to 41.0 average GW.

Rio de Janeiro-based consultancy Abides told BNamericas last month that hydroelectric plants faced a total shutdown by December unless urgent measures were taken to reduce consumption.

Hydropower accounts for more than 75% of Brazil's installed grid capacity.