The Princeton Guide to Ecology

An important new insight is that water in its various forms operates as a system on scales much larger than a single lake, river basin, aquifer, or municipality. Although the global cycling of water through the earth’s physical system (ocean, atmosphere, terrestrial freshwater bodies) has long been recognized, researchers are only now uncovering a much wider net of connectivities that binds together the flow of water on a global scale. The connectivities are physical (e.g., upstream storages of water cause large-scale changes in the residence time of surface water), economic (e.g., water is embedded in food and other products and traded internationally), and even institutional (e.g., decisions about trade of water technology have a global impact). This new awareness of connectivities has spawned the concept of the “global water system.” Recent research has also made it clear that the global water system is undergoing large-scale, unparalleled, and poorly understood changes that pose major risks to ecosystems and society. The policy community needs to respond immediately to these risks, and this response should take place at all levels, from local to global. At the global level, there are three main tasks to take on. First, we need to expand our knowledge base about the global water system by extending the scope of earth observations, by conducting new large-scale field experiments, and by developing new tools for the simulation of the global water system. Second, we should expand global governance of the water system through various means (as a complement to governance at the local and other levels). Options include invoking an international convention on environmental flows, instituting water labeling of products at the international level, and enforcing water efficiency standards of internationally traded products. Finally, we should challenge current assumptions about water use in the world by stimulating a public debate on the definition of “essential water needs” and by broadening the viewpoint of water professionals to include the global perspective.

teleconnection. A cause-and-effect chain that operates through several intermediate steps and leads to a linkage between two parts of a system that (to researchers at least) is unexpected or surprising.

virtual water. The volume of water that circulates in an economic system as an embedded ingredient of food and other traded products. This concept originated from the idea that arid countries compensate for water deficits by importing water-intensive commodities rather than domestically producing these commodities.

Although the Earth is known as the “water planet,” most water researchers and managers focus on scales much smaller than the planetary. Indeed, most freshwater studies concentrate on lakes, streams, or perhaps watershed-scale hydrologic processes, and nearly all water managers concern themselves with planning the water supply in their community or perhaps river basin. Water science and management were basically local activities until “watershed thinking” revolutionized these endeavors in the 1960s and 1970s. Afterward, it became more common for water researchers and engineers to incorporate watershed-wide relationships among climate, runoff, and water use into their work.

Now we are again called on to broaden the perspectives of water science and management. The motivation comes from recent research showing that water is interconnected on a planetary level more tightly and in more ways than previously appreciated.

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