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<br />.. '~j <br /> <br />Two of the currently available post-processing capabilities interact with the model <br />component. The parameter-optimization and sensitivity-analysis tools are provided to optimize <br />selected model parameters and evaluate the extent to which uncertainty in model parameters <br />affects uncertainty in simulation results. A modified version of the National Weather Service's <br />Extended Streamflow Prediction Program (ESP) (Day 1985) provides forecasting capabilities <br />using historic or synthesized meteorological data. <br /> <br />MODULAR MODEL CONCEPTS AND CAPABll.ITIES <br /> <br />Modules <br /> <br />A major feature of the model component of MMS is the module library which contains a variety <br />. of compatible modules for simulating water, energy, and biogeochemical processes. The library <br />can contain several modules for a given process, each representing an alternative <br />conteptualization or approach to simulating that process. The user, through an interactive model <br />builder interface (MBUll.D), selects and Jinks modules to create a specific model. Once a model <br />has been built, it may be saved for future use without repeating the MBUllD step. This capability <br />allows 'canned' versions of models to be provided to end users <br /> <br />Initial modules in the library were derived from the U.S. Geological Survey's <br />Precipitation Runoff Modeling System (PRMS) (Leavesley et aI., 1983). Additional modules <br />have been included using selected process algorithms from the National Weather Service River <br />Forecast System (NWSRFS) model (Anderson, 1973), the Streamflow Synthesis and Reservoir <br />Regulation (SSARR) model (U.S. Anny, 1989), and TOPMODEL (Beven and Kirkby, 1979). <br />New modules for channel transport of solutes and sediment also have been developed and <br />included. Additional modules can be added to the library as research and operational applications <br />expand MMS use. <br /> <br />The ability to link modules developed by a variety of users is provided by the use of a <br />standardized module structure. A module is composed of a minimum of four functions: declare, <br />initialize, run, and main. The declare function is used to specify parameters and variables that are <br />being declared in this module. The initialize function is used to initialize parameter and variable <br />values used in the module. The run function contains the algorithm code that simulates the <br />specific process. The main function directs system calls to the declare, initialize, and run functions <br />of a module. A module can be written in either the FORTRAN or C programming language. <br /> <br />Communication among modules and between a module and the MMS system is <br />accomplished using specific MMS function statements that a module developer uses in the <br />module code. Parameter and variable data structures are created by the "declparam" and "declvar" <br />function statements respectively. When MMS is executed, the declare function of all modules is <br />executed once to obtain the needed infonnation from the declparam and declvat statements to <br />build the MMS parameter and variable data bases. During the execution of the initialize and run <br />functions of a module, related MMS function statements "getparam" and "getvar" are used to read <br />current values of parameters and variables from these data bases. Values are Wrinen to the. <br />,.. '" . ".. "." ' ,j: "r'.. <br /> <br />".) <br />'..,/ <br /> <br />4 <br />