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Overview A Plan for A New Science Initiative on the Global Water Cycle

The global water cycle is central to the Earth’s climate system. It transcends conventional disciplinary boundaries and is a pervasive aspect of the physical, biological, and chemical processes and interactions of the coupled climate system. In addition, water exerts a profound influence on human activities and natural environmental processes. Global change related to anthropogenic effects on climate, land use, and water use increases the uncertainty in forecasts of the water cycle, especially as these forecasts relate to the management of water resources and mitigation of natural hazards. Juxtaposed with increasing human demand for water, this increased uncertainty is cause for the concern among the USGCRP agencies that the existing scientific knowledge of the water cycle is insufficient. In response, the USGCRP empanelled the WCSG, comprised of 16 scientists under the chairmanship of Dr. George M. Hornberger (University of Virginia), to draft a plan for a coordinated research strategy on the global water cycle.

The WCSG structured its research strategy in a matrix-like format with three major science questions, each with three research goals, and three crosscutting pillar initiatives. These pillar initiatives are identified in the water cycle science plan as “research that should be given first priority” (USGCRP, 2001, p. 13). The science questions and related goals are as follows:

Science Question 1: What are the causes of water cycle variations on both global and regional scales, and to what extent is this variation induced by human activity?

Goal 1: Quantify variability in the water cycle.



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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle 2 Overview A Plan for A New Science Initiative on the Global Water Cycle The global water cycle is central to the Earth’s climate system. It transcends conventional disciplinary boundaries and is a pervasive aspect of the physical, biological, and chemical processes and interactions of the coupled climate system. In addition, water exerts a profound influence on human activities and natural environmental processes. Global change related to anthropogenic effects on climate, land use, and water use increases the uncertainty in forecasts of the water cycle, especially as these forecasts relate to the management of water resources and mitigation of natural hazards. Juxtaposed with increasing human demand for water, this increased uncertainty is cause for the concern among the USGCRP agencies that the existing scientific knowledge of the water cycle is insufficient. In response, the USGCRP empanelled the WCSG, comprised of 16 scientists under the chairmanship of Dr. George M. Hornberger (University of Virginia), to draft a plan for a coordinated research strategy on the global water cycle. The WCSG structured its research strategy in a matrix-like format with three major science questions, each with three research goals, and three crosscutting pillar initiatives. These pillar initiatives are identified in the water cycle science plan as “research that should be given first priority” (USGCRP, 2001, p. 13). The science questions and related goals are as follows: Science Question 1: What are the causes of water cycle variations on both global and regional scales, and to what extent is this variation induced by human activity? Goal 1: Quantify variability in the water cycle.

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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle Goal 2: Understand the mechanisms underlying variability in the water cycle. Goal 3: Distinguish human-induced and natural variations in the water cycle. Science Question 2: To what extent are variations in the regional and global water cycles predictable? Goal 1: Demonstrate the degree of predictability of variations in the water cycle. Goal 2: Improve predictions of water resources by quantifying fluxes between key hydrologic reservoirs. Goal 3: Establish a systems modeling framework [i.e., all elements of the system— observing methods, models, risks and values—are evaluated within a common framework] for making predictions and estimates of uncertainty that are useful for water resource management, natural hazard mitigation, decision making, and policy guidance. Science Question 3: How are water and nutrient cycles linked in terrestrial and freshwater ecosystems? Goal 1: Develop observations and experiments that characterize the coupling of water, carbon, and nitrogen cycles. Goal 2: Develop a quantitative predictive framework for water, carbon, and nitrogen fluxes coupled to ecosystem responses. Goal 3: Distinguish human-induced and natural variations in the coupling of water, carbon, and nitrogen cycles. The crosscutting pillar initiatives are the following: Pillar Initiative 1: Determine whether the global water cycle is intensifying and, if so, to what degree human activities are responsible. Pillar Initiative 2: Determine the deeper scientific understanding needed to substantially reduce the losses and costs associated with water-cycle calamities such as droughts, floods, and coastal eutrophication, and incorporate it into prediction systems. Pillar Initiative 3: Develop the scientifically based capacity to predict the effects of changes in land use, land cover, and cryospheric processes on the cycling of water and associated geochemical constituents.

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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle Table 2.1, reproduced from the water cycle science plan, identifies the needs and proposed actions under each of the three science questions. The water cycle science plan is developed around five main chapters: (1) rationale for the science plan, (2) causes of water cycle variation on regional and global scales, and human influences, (3) predictability of variations in regional and global water cycles, (4) determining links between water, carbon, nitrogen, and other nutrient cycles in terrestrial and freshwater ecosystems, and (5) an integrated water cycle science plan. In comparing the science questions posed in Table 2.1 to the water cycle science plan’s chapters, we note that there is a direct correspondence between the central three chapters (Chapters 2–4) and the three questions; in fact, the chapters provide the background and rationale for the science questions.

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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle TABLE 2. 1. Identified Needs and Proposed Actions for Each of the Main Science Questions in the Water Cycle Science Plan Science Question 1 Science Question 2 Science Question 3 What are the causes of water cycle variations on both regional and global scales, and to what extent is this variation induced by human activity? To what extent are variations in the regional and global water cycle predictable? How are water and nutrient cycles linked in terrestrial and freshwater ecosystems? Scientific Gaps • Observations to quantify the variability of relevant water and energy cycle components • Understanding of processes that control water cycle variability • Modeling approaches that can reproduce observed water cycle variability at scales relevant to water resource management • Approaches to partitioning natural and humancaused variations in the water cycle Scientific Gaps • A description of the spatial and temporal regimes within which hydrologic variables can be accurately predicted to orecast floods and droughts • Understanding o luxes among key hydrologic reservoirs to enhance prediction accuracy and reliability • Methods to trans er knowledge effectively from physical climate and hydrologic models to strategies for water resource management Scientific Gaps • Observations of C and N reservoirs and fluxes • Observations o water use and o institutional controls on water use • Understanding of the linkages between changes in land use and changes in water and nutrient cycling • Models of transport of C and N to coastal oceans; fully coupled biosphere- climate models; and coupled models o water demand, agricultural practices, land use, and water quantity and quality Proposed Actions • An observation program using new and evolving technologies to characterize water cycle variability • A new commitment to field studies to resolve uncertainties about water and energy cycles • A model development initiative to reproduce observed water cycle variability and to help discriminate natural and anthropogenic sources o variability • An advanced data assimilation system and products to unify disparate observations, and to reduce uncertainty in estimates o water cycle variability • Use o water and energy budget diagnostics to evaluate model per ormance and to characterize water cycle variability Proposed Actions • Identi ication of predictable water cycle components at all pertinent temporal and spatial scales • Quanti ying prediction uncertainty through a program of monitoring, process studies, and model development • Developing and implementing instruments, methods, networks, and assimilation techniques to estimate the two presently unobserved fluxes, recharge/ discharge and evaporation • An interdisciplinary initiative that uses a systems modeling framework to integrate users ’ requirements into the design and implementation of observing systems, model- based prediction, and forecast verification Proposed Actions • Integrated remote and ground- based observation programs, with observations conducted at a hierarchy of spatial and temporal scales and recorded in a sustainable data archive and retrieval system • Field studies to establish quantitative descriptions o processes relevant to coupled C- N- water cycling • Conjoining observations and models to understand and quantify slower feedback mechanisms o vegetation structural dynamics on coupled C- N- water cycling • Knowledge transfer program for collaboration and communication among researchers, decision makers, and stakeholders SOURCE: USGCRP ( 2001) .