China’s Poyang Lake – permanent areas of water can be seen in blue. Pink shows areas where water is found less often. European Commission - Joint Research Centre, 2016

More of Earth’s surface is covered by liquid water now than three decades ago. But some countries in Central Asia and the Middle East have lost more than half their surface water, satellite images show. There have also been losses in the US and Australia.

The changes are mainly a result of activities such as irrigation and dam building, but climate change is playing a part too.

Previous studies of surface water have largely relied on how much water countries estimate they have. Using satellite images is difficult because water looks very different depending on its depth, what’s in it and so on.


Now Jean-François Pekel at the European Commission’s Joint Research Centre and his colleagues have used artificial intelligence to analyse the entire Landsat archive – three million satellite images from 1984 onwards – and map global surface water with 30-metre resolution. The study gives us the first detailed picture of how surface water is changing.

Overall, the area of land permanently covered by water has increased by around 3 per cent. New permanent waters covering an area of 184,000 square kilometres have formed since the 1980s. Another 29,000 km2 is now seasonally covered by water.

Many new water bodies are a result of dam construction, but lakes are also appearing in places like the Tibetan plateau due to the melting of snow and glaciers in the Himalayas.

Drying up

Elsewhere, 90,000 km2 of permanent waters have been lost – an area equivalent to that of Lake Superior in North America. Another 62,000 km2 have changed from being permanently covered by water to being seasonally covered.

Most of this surface water loss occurred in just five countries: Kazakhstan, Uzbekistan, Iran, Afghanistan and Iraq.

Kazakhstan and Uzbekistan have lost almost the entire Aral Sea – once the world’s fourth largest lake. Iran, Afghanistan and Iraq have lost 56, 54 and 34 per cent of surface water respectively.

The study did not look at why this is happening, but other studies show drought, river diversion and unregulated extraction for irrigation are the main factors.

“It is certain that human action is causing change,” says Pekel.

Bird’s Head Peninsula in West Papua – permanent areas of water can be seen in blue. Pink shows areas where water is found less often. European Commission - Joint Research Centre, 2016

The western states of the US have also been hard hit, with droughts and high water-demand causing a combined 6000 km2 water loss.

The findings are a reminder that permanent water bodies should not be taken for granted, says Wayne Meyer at the University of Adelaide, Australia. “The equation is quite simple. Just like a bank balance, if the outgoings are greater than the incomings, the balance goes down,” he says.

Global water supplies are under pressure because the amount of fresh water needed to produce food for 7 billion people each year is more than half the water in every river of the world, Meyer says.

Yenisei River in Russia – permanent areas of water can be seen in blue. Pink shows areas where water is found less often. European Commission - Joint Research Centre, 2016

The study also highlighted the differences in water availability across the globe. Almost 52 per cent of the planet’s permanent surface water is located in North America, which is home to less than 5 per cent of the global population. By contrast, only 9 per cent of permanent surface water is found in Asia, where 60 per cent of the population lives.

“Our dataset should certainly not be interpreted as a water conflict risk map,” says Pekel. “But treated correctly, it could at least highlight potential sites where tension over trans-boundary resources may arise, and which could ultimately reach a conflict situation.”

Journal reference: Nature, DOI: 10.1038/nature20584

Read more: Many of world’s lakes are vanishing and some may be gone forever