Water security in one blue planet: twenty-first century policy challenges for science.

Water-related risks threaten society at the local, national and global scales in our inter-connected and rapidly changing world. Most of the world's poor are deeply water insecure and face intolerable water-related risks associated with complex hydrology. Most of the world's wealthy face lower water-related risks and less complex hydrology. This inverse relationship between hydrological complexity and wealth contributes to a divided world. This must be addressed if global water security is to be achieved. Using a risk-based framework provides the potential to link the current policy-oriented discourse on water security to a new and rigorous science-based approach to the description, measurement, analysis and management of water security. To provide the basis for this science-based approach, we propose an encompassing definition rooted in risk science: water security is a tolerable level of water-related risk to society. Water security policy questions need to be framed so that science can marshal interdisciplinary data and evidence to identify solutions. We join a growing group of scientists in asserting a bold vision for science leadership, calling for a new and comprehensive understanding of the planet's water system and society's water needs.

Beyond the river: the benefits of cooperation on international rivers.

Management of international rivers can be a cause of conflict or cooperation between states. Benefits of cooperation include benefits to the ecological river, the economic river, the political river and the catalytic river. The challenges are in balancing the trade-offs between states.