System structure and hydrologic models are described as follows:

The first version of the HLRMS is consistent with an HRAP projection, such as computational elements are defined on a sequence of HRAP pixels. Each element consists of a rainfall-runoff component (in version 1 - SAC-SMA model) and a routing component (in version 1 - hillslope/channel kinematic wave model). Rainfall-runoff component generates fast (surface) and slow (subsurface/ground) runoffs. Within each element, a fast runoff is routed over conceptual hillslope to a channel, and then channel inflow combined with a slow runoff component and upstream pixel outflows is routed through a pixel conceptual channel. A conceptual hillslope consists of a number of uniform hillslopes (a number of hillslopes depends on a stream channel density of a pixel). A conceptual channel usually represents the highest order stream of selected pixel. Cell-to-cell connectivity sequence must be determined to move water from upstream to downstream elements and to a basin outlet. An implicit numerical scheme is used for kinematic equation solution.

Data format for input variables and model parameters are similar to 'xmrg' binary type grids with a minor difference in the header. All parameter grids are binary files with two header records. The first record is the same as the 'xmrg' record that consists of X- and Y-orifins of HRAP, and numbers of columns and rows in the file. The second record differs from ‘xmrg' records. It includes two variables: scale factor to convert integer*2 values into real values, and number of bytes per value (2 for integer*2 format, and 4 for real*4 format). This allows to keep grids in integer*2 or real*4 formats. In the first run, the model will read archived ‘xmrg' files directly. In the same time, a separate new binary file will be created for each selected non-nested basin. These new binary files contain precipitation data only for those grids contained in the selected basins. It will greatly reduce the run-time for further model test runs. State variables will be saved as the same format as newly created precipitation data except that they are corresponding to a specific time. During the run time, all grids are converted into one-dimensional arrays in a pixel connectivity order. A number of separate or nested basins can be processed simultaneously. Hydrographs at selected outlets are stored in an OH card format. Selected grids (input variables, states, water balance components) can be stored in an Arc/Info format for a selected period with desirable time interval.

Input variables. Precipitation 'xmrg' hourly grids. Climatological monthly evapotranspiration demand and PE adjustment factor grids. NOTE: Hourly/daily potential evaporation grids can be also used if available.

Initial state variables. Six SAC-SMA upper-lower zone states (UZTWC, UZFWC, LZTWC, LZFSC, LZFPC, ADIMPC), hillslope routing state (water depth of each pixel), and channel routing state (channel cross-section at each pixel) grids.

Parameters. 16 SAC-SMA parameter grids. Hillslope slope, roughness coefficient, and stream channel density grids. Channel slope, roughness coefficient, shape parameter, b, and top width parameter, a, grids. Shape and top width parameters are defined based on a relationship between channel top width and depth, B=a*H**b. The program converts hillslope parameter grids into one basic hillslope parameter grid, a specific hillslope discharge per a unit depth. Four channel grids are converted into two basic channel parameter grids, a specific channel discharge per a unit channel cross-section, and a power value in relationship between discharge and cross-section.

Grid replacement and adjustment. All variable and parameter grids except precipitation can be replaced by some uniform values for each selected basin/subbasin. They can be also adjusted by some ratio for each selected basin/subbasin. An information on replacement or adjustment is provided in an input deck of the HLRMS .