Michael Reinhard/Corbis/Getty Dams are supposed to collect water from rivers and redistribute it to alleviate water shortages, right?
Not so fast.
It turns out that in most cases they actually create water scarcity, especially for people living downstream.
Almost a quarter of the global population experiences significant decreases in water availability through human interventions on rivers, says Ted Veldkamp at Vrije University in Amsterdam, the Netherlands.
They used this to assess water scarcity between 1971 and 2010, so they could identify the hydrological winners and losers from dam interventions.
Learn more at New Scientist Live in London from 28 September to 1 October: Come see our talk on geoengineering – the idea that we can intervene in the climate on a massive scale to reduce the effects of global warming The world has spent an estimated $2 trillion on dams in recent decades.
But Veldkamp’s startling conclusion is that the activity has left 23 per cent of the global population with less water, compared with only 20 per cent who have gained.
“Water scarcity is rapidly increasing in many regions,” says Veldkamp.
Under pressure Many nations see dams as an important way to fight climate change – both by diverting water to alleviate shortages and by generating low-carbon hydroelectricity to replace power stations that burn fossil fuel.
Building more dams “might mitigate tomorrow’s climate change impacts for a certain group of people whilst putting others under pressure today,” she says.