In late August and early September 1999, the U.S. Global Change Research Program (USGCRP) appointed a Water Cycle Study Group (WCSG), chaired by George Hornberger of the University of Virginia, to advise the USGCRP agencies on the development of a Global Water Cycle Program within the USGCRP. Other members of the study group were John Aber, Jean Bahr, Roger Bales, Keith Beven, Efi Foufoula-Georgiou, Gabriel Katul, James L. Kinter III, Randy Koster, Dennis Lettenmaier, Diane McKnight, Kathleen Miller, Kenneth Mitchell, John Roads, Bridget R. Scanlon, and Eric Smith. The aim was to define a USGCRP initiative for fiscal years 2001 and beyond. In appointing the group, Robert Corell (then Chair of the Subcommittee on Global Change Research for the USGCRP) noted, "Deficiencies in our understanding of the global water cycle severely handicap efforts to improve climate prediction and guide water resource planning. Central to this initiative is the establishment of a science community -- based research planning process complemented by an enhanced interagency coordination effort to address the content of this effort for FY 2001 and beyond." A parallel Interagency Working Group (IWG), charged with coordinating agency activities, worked on plans for implementing the science. The IWG is co-chaired by Rick Lawford of NOAA's Office of Global Programs and Robert Schiffer of NASA's Earth Science Enterprise.

The WCSG first met in Washington, D.C., in early September 1999, again in Washington in November 1999, and in Boulder, Colorado, in January 2000. At the meetings in Washington, the group heard from representatives of IWG agencies and developed an outline of its report. The outline identified the three major science questions that guided the study group's subsequent work. Two town hall meetings, one at the American Geophysical Union fall meeting (December 13, 1999), the other at the American Meteorological Society annual meeting (January 13, 2000), provided the WCSG with important input from the broader scientific community. Beginning at the meeting in Boulder, the WCSG drafted a full report and posted it on the WCSG web site (http://ontario.hydro.washington.edu/WaterStudyGroup/), along with a summary of comments from the two town hall meetings. The WCSG held a two-day open meeting for review of the draft report (March 30-31, 2000, at the Bolger Center, Potomac, Maryland). Written comments were also solicited from the wider community. The WCSG considered these many valuable comments and completed its report in the fall of 2000.

This report, "A Plan for a New Science Initiative on the Global Water Cycle", is the result of the yearlong effort by the WCSG. The Plan describes the rationale for an enhanced scientific research effort on the global water cycle over the next decade and poses three key science questions -- about water-cycle variability, about prediction, and about links with ecosystem processes. The necessary ingredients of a new initiative on the water cycle -- (1) improved observations, including innovative measurements using new technologies and networks for coordinated observations, (2) a set of coordinated field, remote-sensing, and modeling experiments, and (3) nested regional climate models to provide a means of linking atmospheric, land surface, and subsurface processes -- are articulated. Finally a set of "pillar initiatives" is put forth as a way to guide the initial efforts of the initiative toward the highest priority and highest payoff areas.

By George Hornberger
University of Virginia
Chair, Water Cycle Study Group