In the report*, the United Nations Environment Programme (UNEP) says that alterations of river flows by dams is a “phenomenon of staggering proportions” and inter-basin transfer schemes will result in changes to drainage conditions with consequent environmental effects.

Other problem issues cited in the report include sedimentation, reductions in freshwater discharge, seasonal peak flows and downstream impacts on agricultural yields and fisheries output.

However, the report acknowledges that efforts are underway to mitigate adverse environmental, social and economic impacts of dams, and added that were needed.

It says that ‘the building of more dams cannot be dismissed, since they can provide significant sources of water’.

The report is describes changes in global environmental circumstances over the last 20 years, since the 1987 publication of “Our Common Future”, the landmark study by the World Commission on Environment and Development – commonly referred to as the Brundtland Commission.

In addition to water resources, the report also covers atmospheric, land and biodiversity conditions worldwide. While noting progress in areas with proven solutions, it says new answers are only emerging for other, persistent problems, such as climate change. As part of its coverage it also refers to the ambitions, and challenges of pursuing the Millennium Development Goals (MDGs).

* The report is the UNEP’s “Global Environment Outlook: environment for development” (Geo-4)