This past summer, heatwaves and drought dried up reservoirs across the world, leading to a decrease in hydropower output, reports Bloomberg. In Europe, the drop in production up to September amounted to 75 terawatt-hours. In China production fell 30% in September, while in the U.S., in September and October hydro production is expected to fall to the lowest level in the past six years.
Extreme weather is making hydropower – the world’s largest source of clean energy – no longer as reliable and effective to fight climate change. Other sources of renewable energy are not as flexible or widely used. Some countries, like Norway and Brazil, rely on dams for more than 50% of their electricity, while at the global level, it generates more electricity than wind and solar together. Moreover, hydropower dams can be switched on when power is needed, the same as thermal power plants. But for that you need to have water.
“Worsening drought conditions as part of climate change will start to limit the availability and dispatchability of hydro reservoirs and lower the capacity factor in places like Southwest China and Western US, ” explains Xizhou Zhou, managing director for power and renewables at S&P Global Commodity Insights.
Large dams are also built to provide water for irrigation and drinking water supplies, and to regulate river flow to allow navigation and prevent floods, further complicating dam operation. Last summer, as drought reduced the river flows in the Yangtze River, the Three Gorges Dam had to retain enough water to allow navigation to the city of Chongqing in central China. The effects of the drought still linger after it ended: in the province of Yunnan, aluminium smelters are operating at reduced capacity to save power and let reservoirs refill before the dry winter season.
Nations have the option of reverting to using more coal and gas, invest in nuclear power, or battery storage for wind and solar energy. Building more power lines to connect power sources in different regions can also help, as well as deploying floating solar panels on reservoirs, to generate electricity and slow evaporation. Extreme weather can affect energy sources in many ways: wildfire smoke and dust storms interfere with solar panels, freezing winter temperatures can affect wind turbines, and drought affects the availability of cooling water from rivers for nuclear plants.
Growing opposition to new large dams in many countries due to their environmental and social impacts combine with new concerns about their dependability as a power source. According to BloomberNEF, from now until 2050, global hydropower capacity is expected to increase by 18%, way behind the expected increases in solar power (8-fold) and wind power (3-fold). Pumped storage hydro systems, which can be paired with intermittent wind and solar power to provide electricity around the clock are not so affected by droughts because they are closed-loop systems. China is planning to develop 270 gigawatts of these projects by 2025, compared to 60 gigawatts of traditional dams.
While the concerns about hydropower highlight the complexity of creating a robust renewable energy system to replace fossil fuels, they also stress how urgent it is to transition to clean energies to mitigate the impacts of a changing climate.