In order to limit the scope of this review, a working definition of a decision support system is needed. L. Adelman has defined decision support systems (DSSs) as ``interactive computer programs that utilize analytical methods, such as decision analysis, optimization algorithms, program scheduling routines, and so on, for developing models to help decision makers formulate alternatives, analyze their impacts, and interpret and select appropriate options for implementation'' ( Adelman [1992], p. 2). Another definition has been offered by S. J. Andriole, who defined decision support as consisting of ``any and all data, information, expertise or activities that contribute to option selection'' ( Andriole [1989], p. 3). A common idea explicit in each of these definitions is that DSSs integrate various technologies and aid in option selection. Implicit in each definition is that these are options for solving relatively large, unstructured problems. Thus, the following working definition of a DSS will be used in this review: A DSS is an integrated, interactive computer system, consisting of analytical tools and information management capabilities, designed to aid decision makers in solving relatively large, unstructured problems.
Interactive computer technologies and decision support systems for studying water resources problems began to appear in the mid-1970s and have been discussed in the water resources literature since the mid-1980s ( Loucks et al. [1985a, 1985b]; Loucks and Fedra [1985]; Johnson [1986]; Labadie and Sullivan [1986]). An excellent overview of the work up until the beginning of the past quadrennial was given by Loucks and da Costa [1991]. The most rapid growth of DSSs in water resources, however, has occurred in the last four years. Rapidly advancing computational ability, the development of user-friendly software and operating systems, and increased access to and familiarity with computers among decision makers are a few of the reasons for this rapid growth in both research and practice. However, the field of computerized DSSs in water resources has not yet reached maturity. One reason for this is a lack of case studies in which the performance of DSSs has been evaluated in the appropriate institutional settings. Other contributing factors are the multidisciplinary nature of DSSs and their theoretical underpinnings and the lack of available methods to measure the effectiveness of them. Nonetheless, developers and users have offered much constructive criticism, pointing out the limitations of current conceptual frameworks and questioning the effectiveness and usefulness of today's DSSs. In fact, developers and users may be the principal driving force behind much of the recent advances and applications in DSS in water resources.
This review will begin with a brief discussion of the perceived need for DSSs in water resources. Following this will be a review of recent advancements in the various computer technologies used for decision support. Finally, applications of DSSs and case studies of particular systems will be summarized. Though it is necessary, for the purpose of organization, to focus on the individual components of a decision support system, the reader should keep in mind that an effective and useful DSS is generally characterized by the integration of computer technologies for the benefit of a decision maker.