Basic GAPS Simulation Exercise

The following is a summary of the instructions for running Basic GAPS with the sample input data included in your Basic GAPS workbook (Basic GAPS.xls). You should have climate, soils, phenology and land cover data in your workbook file. The climate, phenology, and land cover data are located on the 'ClimateInput Example' worksheet and the soils data are located on the 'SoilsInput Example' worksheet. The soils, land cover, phenology data are also located on the data information sheet on the last page of this handout. You will input the soils, land cover, and phenology data from the data information sheet. You will input the climate data directly from the workbook file. GLOBE students from Holmes Middle School in Colorado Springs, Colorado, USA, collected the input data for this simulation. Supplemental data from other sources, as indicated on the data information sheet, were also used.

Running Basic GAPS

1) Getting Started

• Open the Basic GAPS workbook. A dialog box will appear indicating that the workbook contains macros. These macros are legitimate macros that contain the equations for the model simulations. You need to enable these macros for the model to run.
  

2) Input Climate Data

• Click the tab labeled 'ClimateInput Example' at the bottom at the base of the Excel screen. This worksheet contains GLOBE climate data. The column headings from left to right are 'Day', Max Temp', 'Min Temp', 'Rain', 'Snow' (rain equivalent), 'Latitude', and 'Years of Climate Data'.

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• To copy the data: click on cell A3, hold down the 'Shift' key, scroll across to cell G3 then down the spreadsheet till the last data line. These cells will now be highlighted. Then press 'Ctrl' and 'c' at the same time.

• To paste the data: click the tab labeled 'ClimateInput' at the base of the Excel screen, click on cell A3, and press 'Ctrl' and 'v' at the same time. Now all of the data from the 'ClimateInput Example' sheet will be pasted on the 'ClimateInput' sheet.

3) User Interface

• Go to the 'User Interface' worksheet by clicking on the worksheet tab labeled 'User Interface' at the base of the Excel screen. This click will bring you to the 'User Interface' worksheet.

  

4) Input Soils Data

• Under the 'Enter Inputs' heading on the 'User Interface' worksheet click on the "Soils Data" command button. This click will bring you to the 'SoilInput' screen. Enter the soils data located under the 'Soils' heading on the data information sheet for Holmes Middle School (last page of this handout).

  

• A dialog box will then appear ('Runoff') asking if you have vegetative site cover and slope information. Click 'OK'.
  

• A second dialog box will then appear ('Runoff Information').

  

• Click the 'Forest' option button (Holmes Middle School site is in a forested area.) Enter the slope of the site by looking under the 'Soils' heading on the data information sheet. After entering this information, click 'Done'.
  

• After checking your data, click 'OK' on the data checking dialog box caution. This will return you to the 'User Interface' dialog box.
  

5) Input Phenology/Landcover Data

• Under the 'Enter Inputs' heading on the 'User Interface' worksheet click on the "Phenology/Land cover Data" command button. This click will bring you to the 'Green Up/Green Down and Fractional Land Cover' data input screen.

  

• The year of the data collection corresponds to each year of phenology data, i.e., enter '1997' for 1997 phenology data, '1998' for 1998 phenology data, etc. You will enter multiple years of data.

• Enter bud break, full leaf, green down start date, green down end date, year of data collection, latitude, and fractional land cover for each year. The phenology data is located under 'Phenology' and the fractional land cover data is located under the 'Land Cover' heading on the data information sheet for Holmes Middle School (last page of this handout). After entering this information, click 'Done'.

• After checking your data, click 'OK' on the data checking dialog box caution. This will return you to the 'User Interface' dialog box.
  

6) Running the Model

• Click on the "Run Model" command button on the 'User Interface' worksheet.
  

7) Viewing Output

• Outputs from the simulation can be viewed in graph or table format. These can be selected by clicking on the appropriate command button under 'View Results' on the 'User Interface' worksheet.

• Output can be viewed as graphs by clicking on the "View Graphs" command button. There are two options for viewing graphs: dynamically or static. Dynamic graphs show the data being plotted day-by-day while the static graphs show the data after the plotting is complete.

  

• Output can also be viewed as a table in an Excel worksheet by clicking on the "View Table" command button. This Excel worksheet can also be viewed by clicking on the 'Output' worksheet tab at the bottom of the Excel workbook.

  

8) Simulation Exercise

1. View the simulated output in table format. The output table shows daily precipitation and all simulated outputs such as, PET (potential evapotranspiration), PT (potential transpiration), etc.
   
2. View output in graph format. Click the 'User Interface' tab. Under 'View Results' select 'View Graphs.' Under 'Static' select the first five graphs. Click the 'Graph' tab on the bottom portion of the screen.
   
3. Select the 'Max vs Min Temperature' tab at the base of the Excel screen. This graph shows daily maximum and minimum air temperature (º C) for 1997-2003.

   a. Which were the hottest and coldest months for this time period?

   b. What were the maximum and minimum temperatures and when did they occur. (If you place the mouse over a data point it will indicate the date and value for that data point)

4. Select the 'PET, Potential T, Potential Evap' tab at the base of the Excel screen. This graph shows daily potential evapotranspiration (PET), potential transpiration (Pot. Trans.), and potential evaporation (Pot. Evap.). PET is the maximum amount of moisture that, if available, would be removed from a given land area by evaporation from the soil surface and transpiration from vegetation. PET is the sum of Pot. Trans. and Pot. Evap. (PET = Pot. Trans. + Pot. Evap). The units of all three are millimeters of water [mm3 (water)/mm2 (surface area)].
   

   a. During which months was PET the highest and which months was it the lowest?
   

b. What were the maximum and minimum values of PET?

5. Pot. Trans is the maximum amount of transpiration that plants would transpire if the stomatal pores were completely open and the soil profile containing roots was completely wet.
   

   a. During which months was Pot. Trans the highest and which months was it the lowest?
   

   b. What were the maximum and minimum values of Pot. Trans?

   c. How does Pot. Trans compare with PET?
   

6. Pot. Evap is the maximum amount of evaporation that would occur if the soil surface was completely wet.

   a. During which months was Pot. Evap the highest and which months was it the lowest?
   

   b. What were the maximum and minimum values of Pot. Evap?
   

   c. How does Pot. Evap compare with PET? What about Pot.Trans?
   

   d. How do the PET, Pot Trans. and Pot. Evap plots compare with the 'Max vs, Min Temperature' graph?
   

7. Select the 'Actual T vs Potential T' tab at the base of the Excel screen. This graph shows the daily actual transpiration (ActTrans) and potential transpiration. ActTrans is the actual water vapor flux from vegetative surfaces to the atmosphere. ActTrans equals Pot. Trans when the resistance to that flux is at a minimum. This occurs when the stomatal pores on the leaf surface are completely open and the soil water content in the root zone is high. As the soil water content in the root zone decreases and the amount of water available to plants ('Plant Available Water') cannot meet the demand for water by the plants, the resistance to the water vapor flux from the vegetation increases. The stomatal pores begin to close and ActTrans decreases below Pot. Trans.

   a. Which years were actual and potential transpiration equal and which years were they not?
   

   b. Under what conditions would ActTran and PT differ?
   

8. Select the ' Actual T vs Actual Evap' tab at the base of the Excel screen. This graph shows daily actual transpiration and actual evaporation (ActEvap). ActEvap is the actual water vapor flux from the soil surface to the atmosphere. ActEvap is equal to Pot Evap when the resistance to that flux is at a minimum. This occurs when the surface layer of the soil is moist. As the surface layer of the soil dries out, the resistance to the water vapor flux from the soil increases and ActEvap decreases below Pot Evap.

   a. How does this graph compare with 'PET, Potential T, and Potential Evap' graph?
   

   b. Why would these graphs differ?
   

9. Select the 'Precip, Drainage, Runoff' tab at the base of the Excel screen. This graph shows daily precipitation and simulated drainage and run-off.

a. Which were the wettest and driest years for this time period?

b. Was the precipitation evenly distributed throughout the year or was it seasonal? Describe an average year.
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c. How would you describe drainage and run-off for this site?

10. Select the 'Output' tab at the base of the Excel screen. This brings you back to the output table. Scroll across to column W. This shows annual precipitation from 1997 through 2003. Column X shows annual potential evapotranspiration, column Y annual potential transpiration, column Z annual actual transpiration, column AA annual potential evaporation, column AB annual actual evaporation, column AC annual drainage, and column AD annual runoff.
    

    a. Do you see any relationships between these values? If so, which?
    

11. Save these values in a separate worksheet. To do this, select 'Insert' then 'Worksheet' on the top toolbar. This will open a new worksheet. Name the worksheet 'Sim_1' by selecting 'Format' then Sheet' then 'Rename' on the top toolbar. Click the 'Output' tab at the base of the Excel screen and scroll across to cell V1. Hold the shift key down and highlight cell V1 through AD9. Press 'Ctrl' and 'c' keys at the same time. Select the 'Sim 1' tab at the base of the Excel screen. Click on cell A1 and press 'Ctrl' and 'v' at the same time. You will use this data later.
    
    
12. To view a dynamic simulation, return to the 'User Interface' worksheet (click tab at the base of the Excel screen). Select 'View Graphs' and click on 'Soil Water Content by Horizon' under 'Dynamic'. Then select a dynamic graph speed (fast, medium, or slow) and click on graph. This graph shows the volumetric soil water content in each horizon as it changes each day. Volumetric soil water content is the volume of water per volume of soil (m3/m3). This simulation will take a couple of minutes to run.
    

    a. Which times of year was the total volumetric soil water content the highest and which times of years was it the lowest?
    

    b. Why do you think this may be the case?
    

    c. Does the volumetric soil water content differ in each of the horizons? If so, how?
    

    d. Why do you think this may be the case?
    

13. Return to the 'User Interface' worksheet. Select 'View Graphs' and click on 'Plant Available Water Content by Horizon' under 'Dynamic'. Then select a dynamic graph speed (fast, medium, or slow) and click on graph. This graph shows the plant available water by horizon as it changes each day. This is the mass or volume of soil water available for plant uptake (mm of water).

    a. How does this graph differ from the soil water content graph?
    
    b. What do think may explain the differences between these two graphs?
    
    

14. Return to the 'User Interface' worksheet. Under 'Static' select 'View Graphs'. Click on 'Maximum Plant Available Water by Texture'. This graph shows the maximum amount of plant available water each soil texture can hold.
    a. Which soil holds the most plant available water and which soil holds the least? Does this surprise you? Why?
    
    

15. Now you will run another simulation with the same input data except you will assume a forest fire destroyed all the vegetation at this location. Prior to running this simulation delete all the graphs by right clicking on each tab and select 'delete.' Reenter the phenology data and put 0 for the fractional land cover amount. A short-cut method for changing this parameter is to click on the 'Climate Input' tab at the bottom of the Excel screen and scroll over to column R. Change all the current values to 0. Return to the 'User Interface' worksheet and run the simulation.
    

16. Select the 'Output' tab at the base of the Excel screen. This brings you back to the output table. Scroll across to column W and review the annual amounts.

    a. How do these values compare to the values from the previous simulation (see Sim_1 worksheet)?
    
    

17. Graph the different outputs either dynamically or statically.
    

    a. What changes do you notice between this simulation and the other one?
    

    b. Can you think of other effects a forest fire would have at this site?
    

You can down load Basic GAPS software at: http://soil.gsfc.nasa.gov/gaps

If you have any questions please contact:
Jessica Robin (jrobin@ltpmail.gsfc.nasa.gov)