Keyboard short cut: Alt, E, L.
This function is for setting up the constraints on a hydrology autocalibration simulation. There are several system coefficients and several catchment coefficients which may be determined through autocalibration. An autocalibration simulation starts with the current values of the coefficients, and then adjusts them up or down to improve the fit between simulated and observed hydrology data. The following dialog box will appear:
The spreadsheet at the top of the dialog is for setting how the autocalibrator adjusts some System Snow & Ice and Heat & Light Coefficients. In the first column, indicate whether or not the autocalibrator may change the value of each coefficient. In the second and third columns, enter the least and greatest acceptable values for each coefficient. In the last column, enter the maximum (and initial) increment by which the autocalibrator can change the coefficients. The current value for any parameter must fall between the specified minimum and maximum in order to be modified by the autocalibrator.
The rest of the dialog is for setting how the autocalibrator manipulates catchment coefficients. Catchments are put into groups of catchments. The coefficients of all catchments in a group will be changed together during autocalibration. Multiple catchments which share similar soil properties, for example, can be put into a single group. To add a group, click on Add Group. To remove a group, click on Delete Group. To change the catchments in a group, click on the Map behind the dialog to select/deselect catchments. The number of soil layers and all coefficients in the spreadsheet at the bottom of the dialog all apply to the selected group. To view and edit the autocalibration coefficients for a particular group, select the group in the list “Group 1”, “Group 2”, etc. and the coefficients for that group will be displayed and the applicable catchments will be selected on the Map. Set whether or not each coefficient may be changed, the range within which it may be changed, and its maximum change increment. The first three coefficients, Precipitation Weighting Factor, Temperature Lapse, and Detention Storage, are functions of the catchments as a whole. The remainder are Soil Hydrology Coefficients, for which there is a value for each soil layer. The autocalibrator constraints shown in the spreadsheet are the same for all layers, but each soil layer’s values are changed independently of each other soil layer during autocalibration. The current value for any parameter must fall between the specified minimum and maximum in order to be modified by the autocalibrator.
The strategy in setting up an autocalibration is two-fold: first, get a good calibration, and second, get it in a reasonable amount of time. The time required to achieve a calibration is proportional to the number of variables which are adjusted by the autocalibration simulation. The system variables should generally be turned on so they will be adjusted by the autocalibration simulation. All catchments should generally be included in one or more catchment groups. Combining multiple catchments with similar characteristics into a single group will save time. One strategy is to set up catchment groups with only one catchment each but where only the first three variables are changed. Then, multiple catchment groups may be set up where only the remaining variables are changed. If a catchment is included in more than one group, it is important that no single coefficient is changed in more than one group. To calibrate surface elevations of lakes, it is important that any outflow in the .FLO files be accurate. To calibrate river hydrology only, move .OLH files to another directory while the autocalibration is running.