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The hydrologic characteristics of watersheds in semiarid regions are dependent upon many variable and often interrelated factors. A quantitative knowledge of these factors and of their relative influence upon the system as a whole is needed in order to improve the efficiency of watershed management in these areas. In an attempt to develop a comprehensive simulation model of a semiarid watershed, research workers in the Agricultural Research Service considered the electronic quently signed with Utah State University. Analog modeling concepts are based upon the development of basic relationships which describe the various processes which occur within the surface hydrologic system of a semiarid watershed. Once established, the model is applicable to any particular geographic unit by determining the appropriate constants of the hydrologic equations. The analog computer is ideally suited to the many time-dependent differential equations which are encountered in hydrologic systems. To test individual equations and to verify the model, a subbasin of Walnut Gulch watershed in southern Arizona was simulated. In preliminary tests, close agreement was achieved between the observed and computed runoff hydrographs for a single storm. Some progress is also reported in the development of an analog technique to plot isohyetal lines corresponding to selected time intervals during the course of a storm.