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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle 3 Responsiveness of the Water Cycle Science Plan to the USGCRP Charge We summarize here our findings with regard to the water cycle science plan’s responsiveness to the study group’s charge (see Chapter 1). Overall, we found that the water cycle science plan is a well-written document that is largely successful in making the case for an emphasis on an expanded USGCRP research agenda focused on the water cycle. The comments and criticisms that follow should be viewed in this light. Though there are important issues that must be addressed if the water cycle initiative is to meet its promise, we find the water cycle science plan to be a useful first step in planning the scientific pursuit of the vital questions associated with the water cycle. As acknowledged in its preface, the plan is ambitious and "will require diligence and hard work by program managers." The challenges, both financial and programmatic, are clearly stated. We note that for over 25 years, there has been concern related to a lack of understanding regarding the water cycle and how it may be affected by climate change and the subsequent impacts on water resources (NRC, 1974; Waggoner, 1990). Indeed, these and other concerns about climatic change led to the U.S. Global Change Research Act of 1990 (PL 101-606), with Congress establishing the U.S. Global Change Research Program (USGCRP) and instructing federal research agencies to cooperate in developing and coordinating a “comprehensive and integrated United States research program.” This historical perspective is a useful backdrop to place the water cycle science plan in perspective. The references above (NRC, 1974, and Waggoner, 1990), which span over two decades, demonstrate long-standing needs for research on the water cycle. The utility of the water cycle science plan to the cooperating agencies depends on both the focus of the plan established by the specific
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle charges given to the WCSG and the extent to which the resulting science plan provides a basis for effective agency implementation plans. In general, we find that the water cycle science plan is faithful to the charge provided to the WCSG by the USGCRP. This context frames our comments on the utility of the water cycle science plan to the USGCRP agencies. In this chapter comments are provided on the water plan as a whole, followed by comments directed at the six specific charges to the WCSG. Overall Utility of the Water Cycle Science Plan In developing a global water cycle science plan, the WCSG is faced with the existence of a plethora of water research programs and activities that address various aspects of the global water cycle on various time and space scales. As the report notes on page 5 of its summary, “All agencies of the U.S. Global Climate Research Program (USGCRP) have programs related to the water cycle”—as do agencies outside USGCRP. Additionally, USGCRP agencies have water cycle programs that are not considered part of their USGCRP activities. Our committee recognizes that the WCSG developed its plan within this research environment. The WCSG report makes the case that coordination of water cycle research is necessary for making progress in this area of global change science, and the new research resulting from the coordinated program would be greatly beneficial to the nation. The WCSG recommended a coordinated program built around the three science questions, each with three goals (see Chapter 2). These three questions can be summarized as follows: What causes water cycle variability? How predictable is the water cycle? How is the water cycle linked to the nutrient cycle? In addition, three crosscutting, “first-priority” pillar initiatives are provided as guidelines “to know where to begin.” Our committee believes that this is a successful framework for structuring a coordinated water cycle science plan. We grappled with the very broad charge to the WCSG in regard to “a research strategy and science plan” that covered virtually all aspects and components of the water cycle, research related to the application of water cycle science in water management, and the role of water in the nutrient cycle. The WCSG re-
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle port is credible in that it (1) provides a research framework structured around three science questions that our committee also believes capture the important unresolved scientific issues, (2) identifies scientific gaps and proposed actions related to these questions, (3) gives a comprehensive description of the current water cycle research activities, and (4) contains many valuable research activities to address the science questions, including the pillar initiatives as areas of initial agency focus. The committee finds much in the report around which agencies could develop implementation plans. The broad research program, which the water cycle science plan out-lines in general terms, spans and links to a broad spectrum of climate science issues, and it overlaps and interfaces with many USGCRP elements. The broad nature of the subject will result in important items be-ing omitted, and our committee identifies a number of these. There are areas where the report is unclear and provides insufficient detail, and we comment on these. Finally, the report tends not to prioritize activities or strongly recommend a strategy to address scientific goals and initiatives, and we suggest priorities as an input to the overall USGCRP implementation process as we were requested to do in our charge. As examples, the water cycle science plan is heavily focused on the terrestrial components of the water cycle and on related biogeochemical aspects. An important aspect of the global water cycle is to understand the air-sea water and energy exchange, and how these interactions govern water and energy cycles on intraseasonal to centennial time scales and on regional and global scales. These aspects are not discussed in the water cycle science plan. From a programmatic perspective, the water cycle science plan does not articulate, even in general terms, how the global water cycle initiative should be integrated into the larger climate research agenda. It is necessary that the agency implementation plans take each of the broadly stated action items (see Table 2.1) and follow with a further breakdown into specific activities that link or interface them to other USGCRP program elements (or USGCRP agency programs.) Much more work needs to be done by the agencies with respect to prioritization and timing of the proposed activities. Still needed is a clear statement of those elements that can be addressed effectively during the next few years, those that will require a decade or so to develop, and those very long-term goals where readiness is not apparent and which will take more that a decade to develop fully. In this light, we have concerns with the first pillar initiative, acceleration of the water cycle, which with the other pillar initiatives is
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle ranked as a high-priority, near-term research activity. It is recognized that determining any changes to the intensity of the globally averaged hydrologic cycle would serve as an excellent metric for the globally averaged hydrologic response to global warming. At global scales, determining this intensity reduces to evaluating either globally averaged precipitation or evaporation. In practical terms this is infeasible due to a lack of adequate observations. Determining the intensity it requires consideration of the terrestrial, oceanic, and atmospheric branches of the global hydrologic cycle. Before addressing the challenge of determining whether the hydrologic cycle is accelerating, we believe that a necessary first step must be to close the water budget both regionally at the scale of large river basins and globally through a combination of space-based and ground-based observations. If hydrologic science is currently unable to measure fluxes sufficiently accurately to close the water budget at virtually any scale, then it is not clear what measurement strategy could be used to measure “acceleration.” To do this from data alone (or data combined with model results) will require a decade or more of significantly improved observations. Thus, it could be argued that this must be realistically viewed as a long-term objective. But closing the water budget entails a challenging research strategy in itself, including development of the observational strategy, measurement capability, and modeling assimilation support for such closure. Similarly, for Pillar Initiative 2 (relating to understanding water-cycle calamities), basic work is needed to validate the representation of the water cycle in climate models and to describe and, in some cases, first identify the processes linking climate variability to calamitous events. For example, climate variability is implicated as a factor in coastal eutrophication, but capability to predict the occurrence and intensity of episodic eutrophication and related anoxia events has yet to be developed (NRC, 2000a). It appears that the water cycle science plan takes for granted that this basic, foundational work either has been done or results will be available where needed to support the science plan. The success of this pillar initiative is predicated on a coordinated interagency program that makes end-users important drivers of developments in the research and operational communities. Otherwise, the value of predictions for hazards mitigation may be limited. The success of the third pillar initiative, which is directed toward developing the scientific capacity to predict the effects of changes in land use, land cover, and cryospheric processes on the cycling of water and associated geochemical constituents, and which cuts across the science
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle questions, is dependent on developing quantitative benchmarks for models that are used in such assessments. More programmatic guidance on how agencies would develop and use these benchmarks is important; otherwise, the current rate of progress is probably inadequate to realize this initiative. Overall, implementation of the water cycle science plan by cooperating agencies should give priority to basic work in the following three areas: assembling and defining the observational requirements for regional and global and regional water budget variables, establishing quantitative benchmarks for improvements in the characterization of the water cycle components of climate models, and determining the scientific needs of water resource managers, and making these needs the drivers of basic and applied water cycle research. Comments on the Specific Charges Given to the WCSG From these overarching comments, the committee has further comments on the six specific charges that were provided to the WCSG, and we have advice to give to the USGCRP as it develops a water cycle implementation plan. Charge 1. Quantitative understanding of atmospheric, terrestrial, and oceanic interactions that govern water and energy cycles on intraseasonal to centennial time scales and on regional and global scales; this including, inter alia, the roles of water vapor, clouds, and precipitation processes; biogeochemical processes; terrestrial and aquatic ecosystem influences; and the roles of surface and subsurface waters within the overall hydrologic cycle. The water cycle science plan addresses this through Science Question 1, which is focused on understanding water cycle variability; Science Question 2, which focuses on how the water cycle is linked to the carbon and nitrogen cycles; and Pillar Initiative 1, which is to determine whether the water cycle is intensifying. The understanding of linkages between the water cycle processes and biogeochemical processes is the focus of Science Question 3 and Pillar Initiative 3. We have the following comments regarding this broad charge:
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle • Addressing this charge requires spanning a large and disparate community of professionals engaged in water science and management. This is an important goal for water cycle research, but given the existing disciplinary divisions, it is unclear whether the agencies will obtain the guidance from the plan on how to bring together the communities required for this element—or even how to parse the scientific problem into feasible components. In addressing this broad charge, it is easy to overlook important elements. This may have happened with regard to the sea-air interactions, which are not discussed in the water cycle science plan. If sea-air interactions are not adequately addressed, planetary-scale processes, which fundamentally force atmospheric circulation and therefore play a central role in land surface hydrology, will also be difficult to address. • The present ability of agencies to address the causes of water cycle variability, predict this variability, and measure any intensification of the water cycle may be lower than for other elements of the water cycle science plan. We are concerned that the goal of measuring the intensification or acceleration of the water cycle, depends on the sufficiency of the observations that results in first closing water budgets, both regionally and globally. Since both precipitation and evaporation have large un-certainties, determining changes in the residence time of water seems highly challenging. Moreover, identifying the natural versus human-induced variability is a problem of attribution that also seems overly ambitious at this juncture. Background presented in the water cycle science plan (mostly in Chapters 2 and 3) could be clearer in advancing a conceptual model for variability (local versus remote, one-way versus two-way interaction, feedbacks, etc.) needed to provide a “blueprint” for addressing this charge. From such a model, the report could more clearly identify the building blocks for answering the most fundamental question: what are the human-induced versus natural causes of variations and change? Thus, the agencies in coordinating their implementation plans must be assured that this important science question is adequately addressed. • One of the proposed actions in the water cycle science plan is the interdisciplinary initiative to design and implement observing and estimation strategies for quantifying evaporation and recharge. This high-priority issue can only be solved with interagency coordination. The three storages in the water cycle (i.e., atmosphere, surface, and subsurface) are linked by the evaporation and recharge fluxes. Nevertheless, there are currently neither observing networks nor proxy measurements that can provide reliable estimates of these important fluxes. Evaporation and recharge are now mostly estimated as residual of mass balance
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle and therefore also include all measurement errors in the other terms. More direct measurement and estimation techniques need to be devised for these fluxes. Evaporation and recharge are especially challenging fluxes to quantify because the relations and measurements used for their estimation are scale dependent. Furthermore, their spatial and temporal patterns are strongly influenced by biota. Finally, these fluxes mark the place at which the water cycle and the biogeochemical cycle link together. Their estimation at relevant scales where couplings take place is thus especially important. • Regarding understanding the linkages between water cycle and biogeochemical processes, we agree that the carbon cycle should be syn-ergistically studied with the water cycle, and strong links between the U.S. Carbon Cycle Plan (see http://www.carboncyclescience.gov) and the terrestrial water cycle are needed. But other biogeochemical components are equally important to understanding human-induced effects on the nutrient cycle (Science Question 3/Goal 3; and Pillar Initiative 3). Specifically, the water cycle science plan might have called for a stronger effort in addressing the transport, storage, and transformations of sediment and chemical nutrients. For much of the United States, these constituents are the major causes of aquatic system degradation—rele-vant to Goal 2 under Science Question 3. Furthermore, one of the critical issues in carbon cycling is storage of chemical nutrients in sediments. • Lack of an atmospheric chemistry element. The water cycle science plan states that water is the universal solvent. It is also the main source of hydroxyl, the atmosphere's detergent. We note that the plan leaves aside the whole issue of atmospheric chemistry, although other aspects of geochemistry are included. The discussion in the plan regarding water quality (see page 7 of the plan) is interesting in this regard, but we did not see any attempt to draw a connection with U.S. effort to understand atmospheric deposition to water surfaces. (e.g., National Acid Precipitation Assessment Program). In addition, considering upper-tropospheric water vapor (see page 29 of the plan) opens the doors to consideration of atmospheric chemistry, both in the stratosphere and troposphere. This may be beyond the scope of the water cycle initiative, but better observations are certainly needed in the upper troposphere for improved understanding of the water cycle variability. Charge 2. An improved representation of these processes in climate and other models, across the relevant space and time scales, that will allow simulation of the hydrologic cycle and its interactions with the rest of the earth system.
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle The water cycle science plan discusses many of the elements needed to address this charge. In general, Chapter 2 of the plan provides the necessary material related to improving the parameterization of the processes in climate models—namely the five program elements, which are observations, process studies, modeling, data assimilation, and budget studies. We are concerned that these elements describe ongoing and recent activities (observations, process studies, modeling, etc.), but they do not evaluate the appropriateness or sufficiency of these activities for addressing the science questions, nor do they recommend implementation activities needed to move the science forward. The water cycle science plan does not provide a research strategy or sufficient scientific direction to USGCRP agencies to prioritize their implementation activities and carry out the research needed to address the science questions and pillar initiatives central to the water cycle initiative. Charge 3. An understanding of the response of the water cycle to environmental change and accompanying impact on water resources. The water cycle science plan responds well to this element by rec-ommending the development of an integrated approach (“systems modeling framework”) for water resources management to utilize the improved prediction of water cycle variability under Science Question 2. In addition, improved understanding of the water and biogeochemical processes by water and ecosystem management is part of the pillar initiatives. This linkage is consistent with the U.S. Global Change Research Act and the USGCRP assessments (e.g., National Assessment Synthesis Team, 2000; Gleick and Adams, 2000), and thus these elements clearly belong in the water cycle initiative. Under Pillar Initiative 3, a significant part of the scientific effort is directed at the decision processes associated with improved prediction capabilities. Although the water cycle science plan recognizes the importance of these decision processes, more follow-on coordination is needed for the science initiative to help water management agencies develop effective implementation activities. For example, there is a plan to “assist water resources managers in using ensemble forecasts in their operation of water resource systems.” But this presumes that all that is required is straightforward technology transfer. Without specific research, it is unclear whether increased predictive capability will result in sufficiently increased benefits to motivate water managers to adopt new tools and practices. It is important that agency and interagency implementation plans in this area establish the users and operational communities as stakeholders in the research and technology transfer activities.
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle A focus on eventual utility of the science to water managers does serve to provide structure to water cycle studies described in the water cycle science plan, but this research may not serve the most pressing needs of water managers (see, for example, NRC, 2001a). The potential benefits from the efforts described in the water cycle science plan will require more than a transfer of data, forecasts, and techniques described in Chapter 4 of the plan. In fact, there is the possibility that even given the knowledge argued for in the water cycle science plan, benefits to water resource management may be elusive because of an inability to incorporate that knowledge into management procedures. Thus, there is a need to identify an implementation activity that evaluates how new knowledge on the water cycle scientific goals (e.g., predicting climate variability) could be used by water managers. We recommend that the USGCRP include, or at a minimum more actively engage, water management agencies (e.g., Bureau of Reclamation and the U.S. Army Corps of Engineers). Linkages to irrigation districts and local public and private water utilities, which play a critical role in management of water systems, would also be useful. Charge 4. A capability to model and, where appropriate, predict variations in global and regional hydrologic processes and water resources on seasonal to interannual time scales and longer time scales. Science Question 2 and its supporting Chapter 3 address this charge directly. Chapter 3 of the plan has specific goals and program elements, thereby providing a framework to consider Science Question 2. In general, we feel that Chapter 3 of the plan provides an excellent initial foundation from which a research program on predicting water cycle variations can be developed. The concerns listed above under Charge 3, regarding the ability of the water management community to benefit only through technology transfer, are also relevant here, since goal 2 (in Chapter 3) suggests that improved predictions of water resources can occur through improved quantification of fluxes between hydrologic reservoirs (soil water and atmospheric water) without research into water resources decision making. “Improved quantification of fluxes between hydrologic reservoirs” is necessary but not sufficient for improved water management. Charge 5. The requirements for comprehensive, systematic space-based, ground-based, and in situ observations in support of
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle the water cycle science objectives, with consideration of the compatibility of measurements across scales and processes. The WCSG addressed this charge by providing throughout the water cycle science plan descriptions of current observations and potential observations. However, the discussion regarding observations is limited and does not define which observations are critical to the water cycle initiative, which are currently adequate, and which are lacking. Because observations are at the heart of the initiative and are one of the major manifestations of its implementation, special attention needs to be paid to this issue. Based on the science questions and proposed actions in the water cycle science plan, a set of measurement requirements need to be defined for monitoring the water cycle variables. The needed measurement requirements include measurement accuracy, sampling density, and measurement support scale as well as readiness. After the measurement requirements have been defined, the agency and interagency implementation plans can identify the required infra-structure, and its phasing, in proposals. This information would assist the USGCRP and cooperating agencies in defining the necessary obser-vation requirements and in identifying those aspects of their science questions that can and cannot be answered with current and planned observational systems. In addition, the water cycle science plan must rein-force the need for in situ observational networks, which have degraded significantly over the last 20 years. The need for climate quality observational networks has been recognized (NRC, 2001d). The water cycle science plan assumes that new satellite observations (e.g., observations from NASA/EOS and post-EOS-era NPOESS systems) will flow easily into the plan’s research elements and that sufficient ground validation measurements are available to make the new satellite observations useful. Concern has been expressed regarding the sufficiency of climate quality data and whether National Polar-orbiting Operational Environmental Satellite System (NPOESS) will satisfy these needs (NRC, 2000a, b). But we believe that specific agency efforts for both in situ and satellite observations are required to assure adequate observations for the science goals and pillar initiatives presented in the water cycle science plan. Charge 6. Guidance on the linkages, areas of cooperation, and potential integration with other relevant national and international programs to make the initiative a success. The charge to the WCSG included providing guidance to the USGCRP agencies regarding linkages and cooperation with national and international programs. USGCRP requested WCSG’s assistance in four areas related to these linkages: (1) identifying which USGCRP agencies
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle may be best positioned to tackle particular portions of the water cycle plan, (2) identifying non-USGCRP agencies and groups carrying out related water cycle research in the United States with whom the USGCRP agencies should coordinate their research, (3) identifying USGCRP research activities that interface with water cycle science, and (4) identifying international programs with which the USGCRP agencies should coordinate their water cycle science research. We believe that the water cycle science plan has mixed success in providing this advice. In providing advice as to which USGCRP agencies are poised to tackle various elements, the document does provide a comprehensive compilation of activities that need to be undertaken, and the programs in various U.S. agencies (Appendix C of water cycle science plan). However, as part of its guidance to USGCRP, the plan could have provided WCSG’s perspective on how its recommended science plan would be coordinated across USGCRP agencies by matching agency programs with elements of this science initiative. This lack of coordination across USGCRP agencies has been a concern expressed in other NRC reports (see NRC, 2001c). It was not clear to the committee how this vital coordination of work will take place. As part of this coordination activity, we believe that fostering cooperation with non-USGCRP agencies, particu-larly water management agencies, is critical to fulfilling the potential for improved water resource management called for in the water cycle science plan. The water cycle science plan, through its recognition of linkages between water and carbon, has made a very effective case that USGCRP water cycle initiatives should interface with those stemming from the Carbon Cycle Science Plan. The Science Question 3 in the plan—“How are water and nutrient cycles linked in terrestrial and freshwater ecosys-tems?”—provides the opportunity to link to other programs. Many of these are listed in Appendix C of the plan (e.g., NSF’s Long-term Eco-logical Research (LTER) sites, the multiagency National Acid Precipitation Assessment Program, and the USGS Water, Energy, Biogeochemi-cal Budget (WEBB) program, among others). Providing guidance on how the proposed water cycle science initiative and its implementation can interface with these programs is now critically important. With respect to cooperation with international programs, the water cycle science plan lists the activities of many programs (Appendix C of the plan), and U.S. agencies (notably NASA and NOAA) and U.S. scientists contribute significantly to these international climate activities. Still to be designed is a framework on how the new USGCRP water cycle science will contribute to the international climate programs. The need
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Review of USGCRP Plan for a New Science Initiative on the Global Water Cycle for stronger international connections has been noted previously (see NRC, 2001c) and needs to be considered in agency implementation plans. In particular, we believe that there is potential for a stronger international focus with respect to the water resources activities called for in the plan. Understanding and assisting in water resources issues around the world are important to U.S. foreign policy and national security, which implies that these issues should be a high priority for the U.S. hydrologic research and applications communities. In so doing, science can achieve practical advances as well as foster international understanding. Con-tributing to the understanding of water resources and of their links to climate variability seems a nearly ideal way for the United States to step forward to make a scientific contribution that is global not only in its domain of study but also in its domain of application.
Representative terms from entire chapter: