Review of the GAPP Science and Implementation Plan (2005)

The Global Energy and Water Cycle Experiment (GEWEX) Americas Prediction Project (GAPP) was established in 2001 to improve skill in predicting changes in water resources on intraseasonal-to-interannual time scales for the continental United States. GAPP is a follow-on project to a GEWEX Continental-Scale International Project (GCIP) launched in 1995 in the Mississippi River Basin. GAPP builds upon the success of GCIP by expanding the geographic domain of the program and by shifting the program focus from analysis to prediction. GAPP’s focus on land-atmosphere interactions, hydrology, and water resources is consistent with GCIP. GAPP is a continental-scale experiment of GEWEX and is currently the largest GEWEX activity focused specifically on the United States (Lawford 2005).

The seasonal-to-interannual predictability of the hydrologic cycle is related to local and remote influences involving ocean processes (e.g., El Niño-Southern Oscillation) and land processes. Variations in land surface processes and how they affect climate variability are not sufficiently well understood. Recently developed land data assimilation systems have produced more accurate initial surface fields, providing a basis for reducing prediction errors (NOAA-NASA 2004). Although advances in the understanding of land-surface processes show promise in improving climate prediction for water resource management, incorporating climate prediction information into water management decision processes remains a challenge.

In addition to improved understanding of land-surface effects on prediction, water resource managers also need improved precipitation forecasts for interseasonal and interannual time scales. Precipitation forecasts on synoptic time scales have improved greatly in the past few decades, but current models still demonstrate only limited skill in predictions on seasonal and longer time scales. Nonetheless, water managers need long-range forecasts of hydrologic variables related to the surface water budget, and improved predictions would have great economic benefits.

To address these needs, the mission of GAPP “is to demonstrate skill in predicting changes in water resources over intraseasonal-to-interannual time scales, as an integral part of the climate system” (NOAA-NASA 2004). The GAPP program has developed a science and implementation plan (NOAA-NASA 2004) to guide its science activities. Throughout

this report, the science and implementation plan will be referred to simply as “the plan” or “the GAPP plan.” This plan describes strategies for achieving two broad science objectives on the topics of prediction and decision support in the hydrologic sciences (see Box 1). It organizes the program’s research into seven components (NOAA-NASA 2004, Figure 1.1) and describes implementation activities for these components. (Chapter 3 of this report provides detailed analysis of each of the seven components and their associated activities.)

Through 2007, GAPP will continue to be one of the GEWEX continental-scale experiments and a component of the GEWEX Hydrometeorology Panel. GAPP will continue to receive scientific guidance from the GEWEX Scientific Steering Group and the GEWEX Hydrometeorology Panel. Until 2004, the GAPP program within the National Oceanic and Atmospheric Administration (NOAA) was a program line of NOAA’s Office of Global Programs. GAPP has since been merged with the NOAA Climate Variability and Predictability (CLIVAR)-Pan American Climate Studies (PACS) program to form the new Climate Prediction Program for the Americas (CPPA), also within the Office of Global Programs. The rationale for the integrated CPPA is that intraseasonal-to-interannual climate variability is determined by a combination of ocean and land processes and their impacts on the atmosphere. A list of research programs related to GAPP is presented in Table 1-1.

GCIP, the predecessor to GAPP, benefited greatly from a National Research Council (NRC) review published in 1998 (NRC 1998). A number of recommendations were made in the NRC review, including extension of the study beyond the Mississippi Basin to include the semiarid Southwest and the orographic regions of the western United States. In response to the NRC report on GCIP, the GAPP program was initiated with an expanded geographic domain. In 2004, GAPP program managers approached the NRC and requested

a review of the GAPP plan. The NRC committee’s statement of task for the present study is included in Appendix A.

On March 30, 2005, in Washington, D.C., the committee held an information gathering meeting at which presentations were made by the relevant agency program managers and the authoring team of the GAPP plan. (A list of invited speakers and presentations can be found in Appendix B.) The committee then met in closed sessions to deliberate on its findings and recommendations. This report is the product of the committee’s review of the plan.

This report is organized into four chapters. Chapter 1 describes the scientific and policy context of the NRC review of the GAPP plan. Chapter 2 provides the committee’s overarching comments and recommendations for the plan. In Chapter 3, the committee provides comments on and recommendations for the specific chapters of the plan. Finally, Chapter 4 describes how the GAPP science objectives contribute to the objectives of other programs related to GAPP. This review of the GAPP plan is intended to strengthen the plan and thereby strengthen the GAPP program. Appendixes of this report include the committee’s statement of task (Appendix A), the agenda for the committee’s public meeting (Appendix B), a list of acronyms used in this report (Appendix C), biographical sketches of

the committee members and NRC staff (Appendix D), and the full text of the GAPP Science and Implementation Plan (Appendix E).