Inter-basin water transfers (IBWT) offer an approach to addressing water scarcity by confronting the mismatch between water supply and demand in the context of a sustainable development policy. However, IBWTs are often criticized – particularly when the water transfer involves crossing political boundaries. In those circumstances, the policy debate often tends to lose sight of important aspects that guarantee a rational water policy. This chapter addresses issues related to water transfers between river basins, not only in the hydrological term but also, quite frequently, over political boundaries (transboundary water transfer). We present a number of case studies chosen to provide a representative geographical view of IBWTs around the world and insights on the different aspects that involve IBWTs. Intelligent IBWT should be implemented in the context of more general sustainable development strategies and Integrated Water Resources Management.

Water rights and water market mechanisms are key characteristics to describe water management and allocation in the Limarí Basin in Chile. The 1981 Water Code strengthens private water use rights and declares them freely tradable. Engineering infrastructure, climatic conditions, and institutional capacities in terms of tradable water rights and private water user associations allowed economic development in the Limarí Valley. However, the lack of governmental regulation has led to overexploitation of water resources threatening water security, such as environmental and agricultural sustainability. In the face of climate change and decreasing water availability, the current infrastructural and management system requires reforms.

The first chapter introduces a new geological period – the Anthropocene – and explains its origins its timing and importance in emphasizing the current biotic crisis. The current idea that we are in the sixth extinction is criticized because (1) the current level of extinction isn’t high enough to justify it and (2) it limits today’s biotic crisis to just those species that have gone extinct and does not include those under threat. The term defaunation is used in preference because it provides a clearer picture of the situation we find ourselves in. It does this by including both species that have gone extinct and those under threat of extinction. The important concept of the Earth System is outlined and its role in maintaining planetary conditions explained. The link between sudden shifts in Earth System due to climatic forcings and mass extinctions is explained.

This chapter discusses both the role of irrigation in river basin development and closure and how its share in total water use can be reduced. It first briefly outlines the importance of unchecked irrigation development in the growing share of water consumption and the closure process of the basins examined in this volume. This understanding of how irrigation came to play a peculiar role in river basin development is important for discussing how its share can be reduced. The chapter recalls the diversity of policy options available to respond to imbalances between supply and demand and that supply augmentation is generally favored. Finally, the chapter focuses on the issue of "water savings," documenting various responses by the irrigated sector to shortages and exploring how policies to modernize irrigation technologies may inadvertently contribute to enhancing evapotranspiration and therefore undermine purported conservation objectives.

This chapter discusses the impact of river engineering on natural flow regimes and the attendant effects on ecosystems. Changes in flow regimes have resulted in huge ecological change, including the creation of exotic species that replace or compete with the native species. Many rivers in arid regions have growing populations and economic activity dependent on their water supplies. Restoring natural flows may not be possible.

The Rio Grande marks the border between the United States and Mexico, which makes its management particularly complex. A century of engineering and binational governance has shaped the region; today there are multiple reservoirs, diversion channels, and irrigation canals. International and national river managers consider challenges from reservoir sedimentation, population growth, and land use change. Climate change, on the other hand, is barely addressed. Managers must plan for a Rio Grande that by mid-century will have lost 40–50 percent of current water levels. Urban population will have doubled. Irrigated agriculture and cities will continue to use the bulk of available water. The most promising response to meet human and ecological water needs with reduced dependable yield is conservation. To address water scarcity, IBWC/CILA should develop a sustainability plan that balances reduced dependable yield with human and ecological needs. Progress should be reviewed and necessary changes to water allocations be negotiated at 5-year intervals. Irrigation districts, municipal utilities, and environmental stakeholders should work with IBWC/CILA to develop drought management for their sub-basins.

A reservoir is a replacement of a segment of the river with a watercourse that is quite different, a larger, more quiescent water body with different water quality and capable of stratification. This chapter describes design and functions of river reservoirs. The main challenges faced by SERIDAS reservoirs are highlighted. Special attention is given to a reservoir’s dependable yield, which can be maintained constantly without failure throughout the time history of reservoir storage. All reservoirs act as sediment traps and will eventually silt up unless special actions are taken to manage sediment. Reservoirs significantly alter the hydrology of the river downstream from the dam and can affect its water quality and its ecosystem. With increases in population and agriculture, water demands will increase, exacerbated by climate changes. Skillful management will be needed to temper conflicts that arise over how reservoirs will be operated under situations of incompatible objectives.