Parameters or Coefficients.
The Parameters feature from the CRHM pull down menu allows the user to incorporate the physical and spatial data requirements of the modules . The basin/HRU spatial data can be manually inserted into the model or imported as a file with a (.par) or (.dbf) extension. When the model is saved as a project all the parameters are saved with the model in the project file.
The Parameters window displays on the left hand side a list of all available modules. When a module is selected from the Modules box, the spreadsheet displays the number of HRUs, parameter type and parameter value. The Maximum and Minimum value of each parameter is also displayed. It is in this spreadsheet that the parameter value can be highlighted and altered. When the parameter value is selected, the extended description of each parameter is given along with its units. This is visible on the Parameters window on the lower left hand corner to the right of Help and Units.
Basin Parameters are parameters that are shared between modules using identical values. The program when originally loading modules into the model determines which parameters are shared and have the same values for all HRUs and converts them into basin parameters. To make parameters local to a module go to the parameter window and select the module, then click on 'basin' opposite the parameter it is desired to make local. If these local parameters are ever set equal to the basin parameter of the same name, they will resort back to the basin parameter but only after the model is saved and the project is reloaded. Basin parameters are displayed at the bottom of the spreadsheet flagged as 'basin'. Basin parameters are edited by clicking on the module 'basin'. Changes apply to all modules using the basin parameters.
Once established, the parameters for the model can be saved with the File pull down menu. The File pull down Open option allows parameter (.par) files and (*.dbf) files to be imported.
Handling Parameters when Adding/Removing Modules.
Every time a model is 'Built' the parameters in all modules revert back to the default values programmed into the individual modules. To overcome this CRHM queries the user if they want to save the current parameters into a parameter file (.par). After the model is 'Built' immediately re-load using the Parameter screen the original parameters saved in the *.par file. The original model parameters will be loaded if the number of dimension remains the same or is reduced. However, if the number of dimensions is increased the extra dimension of parameters will be set to the values of the last HRU defined in the parameter file. Any new modules added will have the module default parameter values
Parameter Setting Precedence.
When a project is loaded the parameter values are assigned values using the following sequence.
- Module parameters are given the default parameter values defined in the original module code.
- The 'basin' parameters values defined in the project file are given to all parameters of that name (e.g. "hru_area"). Applies to every module or group using the specified parameter.
- Parameters specified by module and group are set to the values given in the project file.
Converting Module parameters to Basin parameters.
CRHM was written to allow individual module parameter values to be different from the global, i.e. basin values for test purposes. To return a module parameters to global parameters, e.g. 'evap - Ht' to 'basin - HT', all the heights must be made identical and the project saved and then the model reloaded from the project file.
Creating a Model from a DataBase File (.dbf).
A new model can be created using parameters created by a GIS. The ArcView® database file (*.dbf) contains the parameters (fields) for all the HRUs (records) in the model. The database file is loaded from the Parameter screen using the file menu before any modules are loaded. The # of HRUs is automatically set to the number of records in the database file and a basin module is created. The user can then proceed to the Build screen and select the desired modules for the model. When the new model is being built, CRHM asks if the current parameters should be saved. Reply YES and supply a file name (.par). After the model is built return to the Parameter screen and load the parameters from the temporary file (.par) that you saved them in.
Incompatible Parameter Names.
CRHM parameter names use upper and lower characters and it appears that the ArcView® database file (*.dbf) must be uppercase only. To manage this problem every parameter name when raised to all uppercase must be unique. For example, hru_GSL and hru_gsl are not unique and represent the same parameter. The actual parameter name appearing in the model is that declared in the first module loaded in which the parameter is used. The following names in the first column are the ArcView® database file (*.dbf) names and the second column gives the CRHM model names as determined from the CRHM module 'basin'.
BASIN_AREA basin_area
HRU_AREA hru_area
HRU_ELEV hru_elev
HRU_LAT hru_lat
HRU_ASL hru_GSL
HRU_ASL hru_ASL