Aging dams and extreme weather are making hydroelectric power less dependable just as countries seek more clean energy

As countries race to expand clean energy, one of their oldest and most trusted power sources is starting to falter. Brazil’s giant Tucuruí Dam, long seen as a pillar of its electricity system, now shows how age and climate change are together weakening hydropower from the Amazon to Asia.

Standing on the Tocantins River in Brazil’s eastern Amazon, Tucurui is one of the country’s largest hydroelectric projects. Built about forty years ago, it is under growing stress from leaks and weather-related damage, reflecting conditions that its original designers did not fully anticipate.

A five-year modernisation programme worth about 270 million dollars is under way. It includes replacing transformers, renewing five of the dam’s 25 generators and automating more of its equipment. The aim is to extend the life of the plant and improve how efficiently it turns water into electricity.

Engineers and analysts, however, caution that such upgrades cannot fully shield hydropower from a changing climate. Longer droughts and irregular rainfall are altering river flows and reservoir levels around the world. In many places, dry periods are followed by sudden heavy rains and flooding, which can damage machinery, fill reservoirs with debris and force operators to halt generation for safety reasons.

Brazil is already seeing the impact. Hydropower still usually supplies more than half of its electricity, yet hydro generation fell by about 3 per cent last year, and actual output is now less than half of installed capacity, even as demand continues to rise. In August, hydropower’s share of Brazil’s electricity slipped to 48 per cent, the lowest in four years, while solar and wind together provided more than one-third of national power for the first time.

Similar problems have been reported in Canada, China, the United States and other countries, raising fresh worries over how to satisfy growing electricity needs while still meeting climate targets.

Globally, hydroelectric output in 2023 recorded its steepest annual drop since records began in 1965, roughly equal to the yearly power use of Chile or the Philippines. Another sharp fall was seen in 2021. The International Energy Agency links these declines mainly to extreme weather tied to climate change, which is disrupting the timing and volume of water that dams rely on.

Yet, despite doubts over reliability and long-standing criticism of the social and environmental damage caused by large dams, some governments continue to push new mega-projects. China is pressing ahead with what is expected to be the world’s largest hydropower plant on the Yarlung Tsangpo in Tibet, a plan that has raised concern in India and Bangladesh about future water availability downstream.

Environmental groups and a number of energy experts argue that governments should place greater emphasis on upgrading and restoring existing dams, rather than clearing new land for large hydro schemes. They point to the displacement of communities and the loss of forests and healthy river systems as heavy costs that are hard to justify.

For Brazil, the story of Tucuruí reflects a wider challenge. Hydropower remains central to its power mix, but the climate conditions that once made it a steady and affordable source of electricity are changing quickly. How the country manages this shift, through modernisation, diversification and planning for more erratic river flows, will be closely watched by other nations that still depend heavily on dams.