The availability of fresh water is potentially one of the most pervasive crises of the coming century. Water-related decisions will determine the future of major ecosystems, the health of regional economies, and the political stability of nations. A vigorous program of research in hydrologic sciences can provide the basis for sound water management at local, regional, national, and international levels. The Committee on Hydrologic Science was established by the National Research Council in 1999 to identify priorities for hydrologic science that will ensure its vitality as a scientific discipline in service of societal needs. This charge will be performed principally through a series of studies that provide scientific advice on the hydrologic aspects of national program and U.S. hydrologic contributions to international programs. This first report contains a preliminary assessment of the hydrologic science content of the U.S. Global Change Research Program (USGCRP). Because this is a short and focused report, little effort is spent to reaffirm the established and successful elements of the USGCRP. In fact, the Committee generally endorses the findings of the National Research Council (NRC) report Global Environmental Change: Research Pathways for the Next Decade (NRC, 1998a; the so-called Pathways report) in this respect. Instead the attention here is directed toward the most critical missing hydrologic science elements in the FY2000 USGCRP. This brings the focus to the terrestrial component of the water cycle. The integrative nature of terrestrial hydrology could significantly strengthen the USGCRP.

In 2001, the U.S. Global Change Research Program produced the report A Plan for a New Science Initiative on the Global Water Cycle. This report was designed to represent a research strategy and scientific plan for investigating the global water cycle, and its interactions with climate and for developing an enhanced understanding of the fundamental processes that govern the availability and biogeochemistry of water resources. The USGCRP managers are currently considering how to move forward with implementation of this ambitious, broad, and potentially very fruitful plan on an interagency basis, and it requested that the National Research Council (NRC) advise them in this regard. This report, Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle, provides comments on the water cycle science plan as related to its recommended scientific initiatives and goals, and it provides comments on the usefulness of the water cycle science plan to the USGCRP agencies in developing a coordinated global water cycle implementation plan.

This report is intended to promote a dialogue between the scientific community and the government officials who will lead our nation in the coming years on global change research. The first section of the report is a brief description of the challenges and proposed responses needed from the highest levels of the government and the second provides more detailed discussion and is directed to agency-level issues and responses. The last section is a detailed bibliography that lists many of the specific reports on which the views outlined here are ultimately based.

Climate theory dictates that core elements of the climate system, including precipitation, evapotranspiration, and reservoirs of atmospheric and soil moisture, should change as the climate warms, both in their means and extremes. A major challenge that faces the climate and hydrologic science communities is understanding the nature of these ongoing changes in climate and hydrology and the apparent anomalies that exist in reconciling their extreme manifestations. The National Research Council (NRC) Committee on Hydrologic Science (COHS) held a workshop on January 5-6, 2010, that examined how climate warming translates into hydrologic extremes like floods and droughts. The workshop brought together three groups of experts. The first two groups consisted of atmospheric scientists and hydrologists focused on the scientific underpinnings and empirical evidence linking climate variability to hydrologic extremes. The third group consisted of water managers and decision-makers charged with the design and operation of water systems that in the future must be made resilient in light of a changing climate and an environment of hydrologic extremes. Global Change and Extreme Hydrology summarizes the proceedings of this workshop. This report presents an overview of the current state of the science in terms of climate change and extreme hydrologic events. It examines the "conventional wisdom" that climate change will "accelerate" the hydrologic cycle, fuel more evaporation, and generate more precipitation, based on an increased capacity of a warmer atmosphere to hold more water vapor. The report also includes descriptions of the changes in frequency and severity of extremes, the ability (or inability) to model these changes, and the problem of communicating the best science to water resources practitioners in useful forums.

Solving problems related to use of water resources will be of paramount importance in coming decades as increasing pressure from growing populations, climate change, extreme weather, and aging water-related infrastructure threaten water availability and quality. The Water Mission Area (WMA) of the U.S. Geological Survey (USGS) has a long-established reputation for collecting and delivering high-quality, unbiased scientific information related to the nation's water resources. WMA observations help inform decisions ranging from rapid responses during emergencies such as hurricanes, floods, and forest fires, to the long-term management of water resources. Produced at the request of USGS, this report identifies the nation's highest-priority water science and resources challenges over the next 25 years. Future Water Priorities for the Nation summarizes WMA's current water science and research portfolio, and recommends strategic opportunities for WMA to more effectively address the most pressing challenges.

Report summarizes and interprets workshop discussions focusing on three areas: Feedback between ecological systems and global change; Consequences of global change for ecological systems; Sustaining and improving ecological systems in the face of global change.