The research, published in a report from the National Center for Atmospheric Research (NCAR) in the USA examined existing river flow records gathered between 1948 and 2004 from 925 rivers – representing 73 per cent of the world’s running water supply. The scientists found that the flow of around a third of the world’s rivers had altered during that time, with more than twice as many showing a decrease rather than an increase.

Although human activity, including dam building and agricultural and industrial use, was responsible for a proportion of the reduced flow, the researchers found that climate change is having a significant effect by altering precipitation patterns and increasing evaporation.

‘In places where decreases occur, it can be a result of a combination of both [human activity and climate change],’ said Kevin Trenberth, head of climate analysis at the NCAR. We analysed not only the river discharge but also the precipitation and other climate influences, which we put into a land surface model to simulate the river flow.’

‘As the population grows, there are increasing demands for fresh water and greater pressure on water supply in many parts of the world,’ added Aiguo Dai, NCAR scientist and lead author of the report. ‘This is a big concern under global warming.’

June 2009