ing exceedingly “flat,”1 with respect to not only rapid dissemination of scientific knowledge but also learning from distant environments currently undergoing rapid change (e.g., deforestation, drought, agricultural expansion, etc.) and predicting future water scenarios in other parts of the world, and (c) the natural world is a highly nonlinear system of interacting parts at multiple scales prone to abrupt changes, tipping points, and surprises (Alley et al., 2003; Taleb, 2007) more often than previously thought possible. What do these realizations mean for the future of hydrologic science?

SCIENTIFIC CHALLENGES

The committee identified three major areas that define the key scientific challenges for the hydrologic sciences in the coming decade: The Water Cycle: An Agent of Change; Water and Life; and Clean Water for People and Ecosystems and provided major findings in these areas in Chapters 2, 3, and 4. Within each major area the committee enumerates some of the most challenging concepts and identifies research opportunities for attaining progress in the field; the main message of each is represented in bold, below. The challenges in these areas are the purview of the various subdisciplines within the hydrologic sciences but also related disciplines and subdisciplines. They span physical-hydrologic sciences, including physical hydrology, geomorphology, paleohydrology, and climate science; biological-hydrologic sciences, including ecohydrology, aquatic ecology, biogeochemistry, soil science, and limnology; and chemical-hydrologic sciences, including chemical hydrology, and aquatic geochemistry. These three major areas reflect both an assessment of intriguing open questions in the field and an assessment of the potential for making significant progress by virtue of previous progress coupled with new ideas, techniques, and instrumentation. Although the committee identifies the three areas separately, it is clear that there are overlaps; many of the specific research questions that will be addressed under the umbrella of these areas will bridge across the three major areas.

Water Cycle: An Agent of Change

Water is a dynamic agent whose influence is central to processes that produced the world as we know it and that will affect its evolution into the future. Many critical questions in this priority area are ripe for study both

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1 The term “flat,” coined by the author Thomas Friedman in his books The World is Flat (2005) and Hot, Flat, and Crowded: Why We Need a Green Revolution—and How It Can Renew America (2008), is used to a describe new era of globalization that allows people and entities around the world to compete, connect, and collaborate.



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