From the Amazon to the Nile to the Mekong, rivers are a lifeblood for many nations, filling taps and irrigation canals and generating hydroelectricity that is powering economic development. But a new study warns that changes to river flows caused by climate change threaten that. Thousands of hydrodams risk being left high and dry by mid-century as global warming takes hold.
On the face of it hydroelectricity seems an obvious antidote to climate change. Hydrodams are among the world’s largest power sources and free of carbon emissions. They could replace the burning of fossil fuels in dozens of countries, allowing economic development without booming emissions of greenhouse gases. Brazil, Egypt, China have led the way.
ut there is a problem. Future droughts risk leaving reservoirs empty. Michelle van Vliet of the Austria-based International Institute for Applied Systems Analysis, an influential east-west thinktank, has crunched the numbers to see how a range of standard climate models predict that river flows will change – and what this means for more than 24,000 hydroelectric power plants round the world. Her findings were published in Nature Climate Change this month.
The findings are stark. She concludes that “climate change will reduce the existing power capacities of hydropower in most regions worldwide”. Up to 74% of current hydrodams will likely see reductions in useable electricity-generating capacity by mid-century.
That is potentially a big threat to fast-growing economies like those in South America, which relies on hydropower for more than 60% of its electricity. Much of Africa, Australia, south-east Asia, the US and southern and central Europe can also expect significant declines in hydropower capacity, she warns.
The future is far from certain. Climate models disagree about the hydrological future for many river systems. Depending on which climate model you choose they may get more water – or less. Such uncertainty should make governments and investors nervous. Hydroelectric dams have a design life of 80 years and more. Betting on river flows remaining secure over that timescale is high risk. And where dams are built, the risks of financial disaster, human suffering and even water wars are significant.
Take the Nile. Egypt is heavily dependent on the river for both electricity from the High Aswan dam, and for irrigating its desert farms. Right now, upstream Ethiopia is building a giant new hydrodam, the Grand Renaissance dam, that Egyptians fear could jeopardise flows and threaten their power supplies.