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n Scientific Priorities Science has developed as a cultural endeavor of value to society for the enrichment of the human spirit that flows from understand- ing, as well as for the material benefit to which understanding often leads. The culture of science draws its strength from the diversity of interests, experiences, and viewpoints of its individual investigators, and from its traditional principles of integrity and precision. Few question the wisdom of public financial support for science, but most freely acknowledge practical limits to public altruism. Na- tions and agencies cannot support every scientific proposal, and thus priorities must be set. Although the political process ultimately determines what gets funded, it is in everyone's best interest that this process have the benefit of knowledgeable scientific opinion. Scientists must learn to formulate and advocate research priorities in their separate scientific disciplines. This chapter outlines a rational process by which priorities might be set to promote a vigorous and beneficial hydrologic science. It includes a few examples of research opportunities that the committee believes to be the most important at this time. In addition it names those developments in education and scientific data viewed as necessary for the vigor of hydrologic science in the long term. THE PROCESS The dilemma in the objective establishment of scientific priorities is that the criteria for ranking one opportunity with respect to another are inherently subjective. The 18 members of this committee offered 296
SCIENTIFIC PRIORITIES 297 10 separate but not necessarily independent measures of worth. Each member ranked all 10 in descending order of importance by his or her personal scale of values, and the rankings were averaged across the committee. The interdependence of many of the 10 measures allowed consolidation of the averaged rankings to three criteria: 1. Expected contribution to scientific understanding Including such measures as either breakthrough or incremental contributions to understanding and reduction of uncertainty, this premier criterion reflects the dominating objective of science. 2. Support of a viable scientific infrastructure Maintenance of a cadre of hydrologic researchers and synergistic stimulation of related sciences are among the measures leading to this second-ranked criterion. 3. Contribution to problem solving Social benefits such as the solution of current crises and the opti- mization of water resources were measures of importance yielding this third-ranked criterion. THE PREMISES The diversity and range of scale of the frontier problems in hydro- logic science are illustrated clearly by the examples given in Chapter 3. In addressing the issue of priorities among such questions, we must seek to maintain options and diversity, and to keep avenues open for innovation and the operation of serendipity. The above criteria must be augmented with a set of premises: · It is not possible to make rational priority judgments among very specific research questions. For example, which is more important, the effects of chemistry and biology on soil properties, or how heat and mass flow control water seepage in frozen media? Instead of such fine-grained comparisons, we should consider the relative importance of larger classes of prob- lems, such as land surface-atmosphere interactions versus the generation of streamflow from precipitation. · If the number of priority research areas is kept small, the list need not be ranked. However, if the categories are too broad they become all-inclusive, and the sense of direction is lost.
298 OPPORTUNITIES IN IN THE HYDROLOGIC SCIENCES · In selecting the priority areas only the primary criterion should be used. Satisfaction of the secondary and tertiary criteria should not be allowed to influence membership on the short list but might be used to rank order this list if desired. · The questions with the greatest potential for a contribution to understanding lie at the least-explored scales and in making the linkages across scales. Considering that the historical development of hydrologic science began at the small catchment scale and has spread both ways (i.e., both larger and smaller) over time, rich frontiers lie at the global scale and the microscale. Finding the scale-bridging laws of hydrologic similarity will reveal order and pattern. · Hydrologic science is currently data-limited. Interest in ever-increasing scale has outrun the financial support for observation, and the balance of hydrologic science is now seriously skewed toward modeling. It is important that observation and analysis proceed hand in hand. PRIORITY CATEGORIES OF SCIENTIFIC OPPORTUNITY (UNRANKED) In keeping with the above premises, the committee suggests the following five research areas as those now offering the greatest expected contribution to the understanding of hydrologic science. · Chemical and Biological Components of the Hydrologic Cycle In combination with components of the hydrologic cycle, aqueous geochemistry is the key to understanding many of the pathways of water through soil and rock, for revealing historical states having value in climate research, and for reconstructing the erosional history of continents. Together with the physics of flow in geologic media, aquatic chemistry and microbiology will reveal solute transformations, biogeochemical functioning, and the mechanisms for both contamination and purification of soils and water. Water is the basis for much ecosystem structure, and many ecosystems are active participants in the hydrologic cycle. Understanding these interactions between ecosystems and the hydrologic cycle is essential to interpreting, forecasting, and even ameliorating global climate change.
SCIENTIFIC PRIORITIES 299 · Scaling of Dynamic Behavior In varied guises throughout hydrologic science we encounter questions concerning the quantitative relationship between the same process occurring at disparate spatial or temporal scales. Most frequently perhaps, these are problems of complex aggregation that are con- founding our attempts to quantify predictions of large-scale hydrologic processes. The physics of a nonlinear process is well known under idealized, one-dimensional laboratory conditions, and we wish to quantify the process under the three-dimensional heterogeneity of natural systems, which are orders of magnitude larger in scale. This occurs in esti- mating the fluxes of moisture and heat across mesoscale land surfaces and in predicting the fluvial transport of a mixture of sediment grains in river valleys. It arises in attempting to extend tracer tests carried out over distances of 10 to 50 m in an aquifer to prediction of solute transport over distances of hundreds of meters to kilometers. It oc- curs in extrapolating measurements of medium properties in a small number of deep boreholes (as in the Continental Scientific Drilling Program) to characterize fluid fluxes at crustal depth. The inverse problem, disaggregating conditions at large scale to obtain small-scale information, arises commonly in the parameterization of subgrid-scale processes in climate models and in inferring the subpixel properties of remote sensor images. Solving these problems will require well-conceived field data collection programs in concert with analysis directed toward "renormalization" of the underlying dynamics. Success will bring to hydrologic science the power of generalization, with its dividends of insight and economy of effort. · Land Surface-Atmosphere Interactions Understanding the reciprocal influences between land surface processes and weather and climate is more than an interesting basic research question; it has become especially urgent because of accelerating hu- man-induced changes in land surface characteristics in the United States and globally. The issues are important from the mesoscale upward to continental scales. Our knowledge of the time and space distributions of rainfall, soil moisture, ground water recharge, and evapotranspiration are remarkably inadequate, in part because historical data bases are point measurements from which we have attempted extrapolation to large-scale fields. Our knowledge of their variability, and of the sensitivity of local and regional climates to alterations in land surface properties, is especially poor. The opportunity now exists for great progress on these issues for
300 OPPORTUNITIES IN IN THE HYDROLOGIC SCIENCES the following reasons. Remote sensing tools are available from air- craft and satellites for measurement of many land surface properties. Critical field experiments such as the completed First ISLSCP Field Experiment (FIFE) and the Hydrologic-Atmospheric Pilot Experiments- Modelisation du Bilan Hydrique (HAPEX-MOBILHY), and others under way and planned, promise to improve both measurement and under- standing of hydrologic reservoirs and fluxes on several scales. Additional experiments in a range of environments are needed. Finally, numerical models exist that are capable of integrating results from regional and global measurement programs and focusing issues for future experi- ments. · Coordinated Global-scale Observation of Water Reservoirs and the Fluxes of Water and Energy Regional- and continental-scale water resources forecasts and many issues of global change depend for their resolution on a detailed understanding of the state and variability of the global water bal- ance. Our current knowledge is spotty in its areal coverage; highly uneven in its quality; limited in character to the quantities of primary historical interest (namely precipitation, streamflow, and surface water reservoirs); and largely unavailable still as homogeneous, coordinated, global data sets. The World Climate Data Program (WCDP) has un- dertaken the considerable task of assembling the historical and current data, and the World Climate Research Program (WCRP) is planning the necessary global experimental program, the Global Energy and Water Cycle Experiment (GEWEX) (see discussion in Chapter 4), to place future observations on a sound and coordinated scientific foundation. Many nations must contribute for this program to be successful. The United States should play a major role in GEWEX through the support of key experimental components and accompanying modeling efforts. Of particular importance in this regard is NASA's Earth Observing System (EOS) program (see discussion in Chapter 4), which will include observing and data systems as well as scientific experiments for multidisciplinary study of the earth as a system. · Hydrologic Effects of Human Activity For at least two decades hydrologists have acknowledged that humans are an active and increasingly significant component of the hydrologic cycle. Quantitative forecasts of anthropogenic hydrologic change are hampered, however, by their being largely indistinguishable from the temporal variability of the "natural" system. Experiment and analysis need to be focused on this question. Identification of the signal of change within the background noise of
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302 OPPORTUNITIES IN IN THE HYDROLOGIC SCIENCES spatial and temporal variability will require observations at regional scale and over many annual cycles. Forecasting the course of future change will be eased by understanding what changes have already occurred. DATA REQUIREMENTS · Maintenance of Continuous Long-Term Data Sets The hydrologic sciences use data that are collected for operational purposes as well as those collected specifically for science. Improvements in the use of operational data require that special attention be given to the maintenance of continuous long-term data sets of established quality and reliability. Experience has shown that exciting scientific and social issues often lead to an erosion in the data collection programs that provide a basis for much of our understanding of hydrologic systems and that document changes in regional and global environments. · Improved Information Management The increasing emphasis on global-scale hydrology and the increasing importance of satellite and ground-based remote sensing lead to use of large volumes of data that are collected by many different agen- cies. An information management system is needed that would al- low searching many data bases and integrating data collected at dif- ferent scales and by different agencies. · Interpretation of Remote Sensing Data Effective use of remote sensing data is now too difficult for many hydrologic scientists, because the interpretation often depends on a detailed knowledge of sensor characteristics and electromagnetic properties of the surface and atmosphere. Hydrologic data products should be made available in a form such that scientists who are not remote sensing experts can easily use the information derived. . · Dissemination of Data from Coordinated Experiments Special integrated studies, such as HAPEX, FIFE, and GEWEX, that involve intensive data collection and investigation of the fluxes of water, energy, sediment, and various chemical species, produce high- quality data sets that have value lasting far beyond the duration of the experiment. Optimal use of these data requires broader and more timely distribution beyond the community of scientists who are involved in the experiments.
SCIENTIFIC PRIORITIES 303 EDUCATION REQUIREMENTS · Multidisciplinary Graduate Education Program The broad range of education inputs to graduate study in hydro- logic science necessitates the formation of a multidisciplinary program in the hydrologic sciences. This program should be either a department unit or a confederation of faculty from host departments that is as- sured of autonomy and resources by upper-level administration. If it is the latter type of organization, it may or may not be degree-granting. The primary purpose of the program would be to educate graduate students who are considered first and foremost as hydrologists, not geologists, geographers, or engineers who have some background in hydrology. · Experience with Observation and Experimentation The changing nature of hydrologic science requires the development of coordinated, multidisciplinary, large-scale field experiments. Graduate students should be given experience with modern observational equipment and technologies within their university programs, and mechanisms should be developed to facilitate their participation in these experiments, irrespective of their university of study. When the experiments are planned, the inclusion of a diverse array of studies should be an integral part of the plan. Undergraduate students of science should have experience with measurement of natural phenomena, preferably in field situations as well as in controlled laboratory settings. · Visibility to Undergraduate Students Programs should be developed to make hydrologic science more visible as a scientific discipline to undergraduate students. These programs should include such elements as research participation, in- ternships at laboratories and institutes, curricula that introduce the latest innovations, visiting distinguished lecturers, media development, and in-service institutes for teachers. SOURCES AND SUGGESTED READING Dutton, J. A., and L. Crowe. 1988. Setting priorities among scientific initiatives. Am. Sci. 76(Nov.-Dec.):599-603. Press, F. The Dilemma of the Golden Age. Address to the members of the National Academy of Sciences, April 26, 1988.