The ET Compare Model - Explore OMS Features Using Evaoptranspiration Modules

This problem will familiarize the user with selected features of the OMS Console. It uses two existing evapotranspiration (ET) modules to build a simple ET model. One possible application of OMS is to evaluate alternative concep­tualizations of a single physical process. In this example we will evaluate the Hamon and Modified Jensen-Haise methods for computing potential evapotranspiration (POTET).

Modified Jensen-Haise

daily_potet[i] = jh_coef[mo] * (tavgf[i] - jh_coef_hru[i])*rin

• jh_coef is the monthly air temperature coefficient used in Jensen-Haise potential evapotranspiration computations,
• jh_coef_hru is the air temperature coefficient used in Jensen-Haise potential evapotranspiration computations for each HRU,
• rin is the daily solar radiation expressed in inches of evaporation potential, and
• tavgf is the average HRU temperature, in deg F.

Hamon

daily_potet[i] = hamon_coef[mo]*dyl*dyl*vdsat

• hamon_coef is the monthly air temperature coefficient used in Hamon potential evapotranspiration computations,
• dyl is the hours of daylight for each day, in units of 12 hours, and
• vdsat is the saturated water-vapor density (absolute humidity) at the daily mean air temperature (0 C) in grams per cubic meter (g/m3) computed by (Federer and Lash, 1978)

Open the console

Start the OMS Console from the previously installed directory oms-3.1rc4-console. In that directory double click on the console.bat file.

After the Console window opens, use the Working Directory browse button (blue file folder) in the upper right hand corner to locate and select the PrmsOmsWork project you downloaded and installed at C:\PrmsOmsWork (or where ever you placed PrmsOmsWork).

Click on the open simulation icon to start the process of selecting a .sim file to execute. This will open a browse window in which you can navigate to simulations and then to etComp.

Here select the etComp.sim file, and then click Open. This will load the etComp.sim file into the Console. The OMS Console provides a number of functions through the application icons on the Console tool bar. Moving your cursor over an icon will produce a text box with the name of function provided by the icon. The icons are numbered in the figure below and their function is described below the figure.

1. Create a new, empty simulation.
2. Open an existing simulation from <working directory>/simulations.
3. Save all open simulations.
4. Select options and settings (show hidden files, folders; clear output before next run)
5. Create a new project
6. Close current project
7. Open project
8. Save simulation script to a file. If the file is new, it will prompt for a name.
9. Run the simulation script.
10. Interrupt and stop a running simulation. If no simulation is running this button is disabled.
11. Open the parameter editor with parameter file used in the current simulation. The parameter editor is explained in a section below.
12. Execute the analysis part of a simulation. This will usually result in an new window containing graphs and plots. The analysis window is explained in more detail below.
13. Creates Docbook5 documentation of the simulation and stores it into the current output folder.
14. Build model (alternative to building with Netbeans or other IDE)
15. Open the last output folder using the operating system's file explorer.
16. Clear the console output for this simulation.
17. Logging setting. Define the log level here for your simulation, this will result in more or less verbose output during simulation execution.

Editing Parameter

The model being run contains components for both the Hamon and the Modified Jensen-Haise PET methods. Open the parameter file by clicking on the editor icon.

Click on the down arrow in the Filter window and select the dimension of nmonths. This will convert the parameter file to a spreadsheet format.

Note that both the hamon_coef and the jh_coef parameters are contained in the parameter file. Also note that the 12 monthly values are listed from 0-11 and not 1-12. The 0-11 form is consistent with array numbering in the Java programming language. At this time the user must think in terms of the usual sequencing of 1-12 for months but make the translation when working with the spreadsheet.

Run the model by clicking on the Run icon in the toolbar. When the model completes you will see a set of statistical measures that relate to the fitting of the Hamon computed PET to the Jensen-Haise computed PET.

Run the model

The ns value is the Nash-Sutcliffe Coefficient of Efficiency,absdif is the sum of the Absolute Difference measure, trmse is the Transformed Root Mean Squsre Error. See the OMS Handbook for a full explanation of these measures.

Click on the Analysis icon to display the graphical results of the model run.

The graph shows that the Hamon PET values are lower than the Jensen_Haise values. To increase the computed Hamon PET values increase the monthly values of the hamon_coef parameter. To do this open the parameter editor and select the monthly value spreadsheet. Select all the hamon_coef parameter values by clicking on the parameter cell at the top of the column and then holding down the left mouse button, drag down the column to the last value. Then in the computation window type *2 and then hit the enter key. This will multiply the selected parameter values times 2.

Modifying parameter values is accomplished using mathematical equation format. Examples are as follows:

*2  multiply by 2
/2   divide by 2
+2  add 2
-2   subtract 2
=2  copy 2

More detailed math equations can also be used.

After adjusting the hamon_coef, click on the save file icon in the upper left corner of the edit window to save the changes. Then run the model again and evaluate the results using the statistical measures and the graphical output.

Repeat this process until the Hamon model output matches the Jensen-Haise model output. You may have to adjust individual monthly values to get the best fit. Stop when you have a reasonable match.