摘要：The views of many scientists about water are evolving towards a systems approach that accommodates both the multi-faceted dimensions of water resources and the accelerating pace of globalization and human development. The water system includes the water cycle and three major interacting elements: the physical, biological and biogeochemical, and the human components. Major drivers of change that affect the system are climate change, population growth, land cover change, the development of water diversions, economic development, and governance. Changes in any component of the system will cascade throughout the whole system. Research is needed to clarify the magnitude and mechanisms of change, and how society can best adapt to the system state changes. We need to develop condition indicators such as water availability per person, the water poverty index, pollution concentrations and source water quality. Also on the research agenda are new concepts, namely: blue and green water and environmental flows; virtual water in agricultural trade and associated nutrient flows; and the water systems discourse to integrate natural science and social science approaches. Water governance is a central issue to these concepts. There is a clear need to analyze the impacts of different types of governance of national and regional water resources in a global context.
