Modeling of the rainfall-runoff process is of both scientific and practical significance. Many of the currently used mathematical models of hydrologic systems were developed a genera tion ago. Much of the effort since then has focused on refining these models rather than on developing new models based on improved scientific understanding. In the past few years, however, a renewed effort has been made to improve both our fundamental understanding of hydrologic processes and to exploit technological advances in computing and remote sensing. It is against this background that the NATO Advanced Study Institute on Recent Advances in the Modeling of Hydrologic Systems was organized. The idea for holding a NATO ASI on this topic grew out of an informal discussion between one of the co-directors and Professor Francisco Nunes-Correia at a previous NATO ASI held at Tucson, Arizona in 1985. The Special Program Panel on Global Transport Mechanisms in the Geo-Sciences of the NATO Scientific Affairs Division agreed to sponsor the ASI and an organizing committee was formed. The committee comprised the co directors, Professor David S. Bowles (U.S.A.) and Professor P. Enda O'Connell (U.K.), and Professor Francisco Nunes-Correia (Portugal), Dr. Donn G. DeCoursey (U.S.A.), and Professor Ezio Todini (Italy).

Hydrological Systems Modeling is a component of Encyclopedia of Water Sciences, Engineering and Technology Resources in the global Encyclopedia of Life Support Systems (EOLSS), which is an integrated compendium of twenty one Encyclopedias. This 2-volume set contains several chapters, each of size 5000-30000 words, with perspectives, applications and extensive illustrations. It carries state-of-the-art knowledge in the fields of Hydrological Systems Modeling and is aimed, by virtue of the several applications, at the following five major target audiences: University and College Students, Educators, Professional Practitioners, Research Personnel and Policy Analysts, Managers, and Decision Makers and NGOs.

Deterministic Methods in Systems Hydrology presents the basic theory underlying the multitude of parameter-rich models which dominate the hydrological literature. Its objectives are to introduce the elements of systems science as applied to hydrological problems; to present flood prediction and flood routing as problems in linear systems theory, clarifying the basic assumptions and evaluating their accuracy; and to review and to evaluate some deterministic models of components of the hydrological cycle, with a view to assembling the most appropriate model of catchment response, for a particular problem in applied hydrology. The material is developed in two parts: the first four chapters present the systems viewpoint, the nature of hydrological systems, some systems mathematics and their application to direct storm runoff. The final four chapters cover linear conceptual models of direct runoff, the fitting of conceptual models to data, simple models of subsurface flow and non-linear deterministic models.