Description of model

Figure 1 - A basic model of soil water content

Since the precipitation rate and the evaporation rate are actually not exactly in phase with each other, a slightly phase-shifted function (sot(n)) is used to drive the evaporation rate calculations while sat(n) is used for the precipitation rate (figure 3).

Figure 2 - Temperature profile versus time for evaporation rate calculations

Figure 3 - Temperature profile versus time for precipitation rate calculations

Once the system has been created and established, it's time to start making modifications to better reflect observed climatological changes.  One observed scenario is that while the temperature profile does not significantly change, the amount of water in the soil begins to decrease and eventually falls away to zero. Even with this basic model, we can proposed possible mechanisms which would account for this observation.

In particular, we are interested in incorporating a feedback loop between the rate of evaporation and the rate of evaporation. This is schematically shown below in figure 4.

Figure 4 - A basic model of soil water content with feedback loop

Procedure

1. Obtain the Excel spreadsheet.
2. Table of constants from introduction and the corresponding cells in the spreadsheet.
3. Carry out the experimental runs described in Table 2.1 and print pages 1-4 for each run. Each experimental "run" evolves from its predecessor(s) by varying a single variable/parameter.
4. Analyze the data and draw conclusions about the data. Although certain sets of data will extend beyond 4 years, the first 4 years (shown in the graphs) will generally give enough information see any differences which develop between experiments. You will only need to print out pages 1, 3, and 4. Page 2 contains graphs of the atmospheric conditions which are exactly determined in this model (they do not vary with the choice of experimental parameters). Pages 5-29 will be blank. The numerical data is contained on pp. 30-58 and do not need to be printed out.