Study warns global rivers are drying up

Some of the world's largest rivers, including the Ganges, the Niger and the Colorado, are drying up as a result of climate change, with potentially catastrophic consequences for many of the world's most populous regions and cities.

That is the stark warning from a major new study undertaken by the US National Center for Atmospheric Research, which found that one-third of the world's mightiest rivers have seen significant changes in flow levels over the past 50 years, largely as a result of climate change.

The comprehensive study assessed 925 rivers using both satellite data and on the ground measurement, and found that while the flow in some rivers had increased as a result of changing rainfall patterns and glacial melt water, a significantly larger number had lost water.

Overall, the study found that from 1948 to 2004, annual freshwater discharge into the Pacific Ocean fell by about six per cent, or 526 cubic kilometres – approximately the same volume of water that flows out of the Mississippi river each year. Similarly, the annual flow into the Indian Ocean dropped by about three per cent, while the flow of the Columbia river in the US declined by about 14 per cent.

In contrast, annual river discharge into the Arctic Ocean rose about 10 per cent, primarily as a result of higher temperatures leading to increased levels of glacial melt water.

The study, which will be published next month, warned that if unchecked the trend could have dire consequences for food and water supplies in many of the world's most populous regions.

It also predicted that those rivers that have seen stable or increased flows, such as the Brahmaputra in South Asia and the Yangtze in China, could wither as inland glaciers melt and rainfall patterns change as a result of climate change.

"Reduced runoff is increasing the pressure on freshwater resources in much of the world, especially with more demand for water as populations increase," said Aiguo Dai, a scientist at the NCAR and lead author of the report. "Freshwater being a vital resource, the downward trends are a great concern."

Regions facing the greatest threat include those dependent on the Niger in West Africa, the Ganges in South Asia and the Yellow river in China, while large areas of the western US could be impacted by the reduced flow of the Colorado river.

The study comes as officials in Australia warned that parts of the Murray river are running so low that Adelaide could run out of water within two years.

Water levels in Australia's largest river are at their lowest level on record following a six-year drought and fears are mounting that large parts of South Australia could face even more stringent water-saving measures if the drought does not break soon.

In related news, Oxfam International released a report this week warning that aid agencies could be overwhelmed within seven years as a result of the increased incidence of climate change-related disasters.

The study showed that the number of people impacted by extreme weather events has doubled within 30 years and is likely to increase by a further 54 per cent by 2015, based on the latest climatic predictions.

The report concludes that global emergency spending will have to be nearly doubled to $25bn (£17.2bn) a year, while developing nations will need to be provided with significantly increased funding for investment in climate change adaptation measures. It said that under any UN climate change deal agreed later this year, rich countries should deliver a medium-term commitment to spend $42bn a year to help poorer nations adapt to unavoidable climate change, rising to at least $50bn a year in the longer term.