Note: The user is cautioned on the use of evaporation and evapotranspiration in VS2DH. These processes can influence and be influenced by soil temperature. As described in Lappala and others (1987) and implemented in VS2DH, these processes are assumed to be isothermal. Users should evaluate the ramifications of this assumption in their applications. If these processes are an integral component of an application, then use of another numerical model that treats evaporation and evaotranspiration in a more realistic fashion may be warranted.
If neither evaporation (over bare soil) nor transpiration (plant root extraction) is simulated, this step may be skipped.
Evapotranspiration (evaporation + transpiration) is simulated as a recurring cycle (see figure). The cycle is composed of evapotranspiration periods of equal duration. Evapotranspiration parameters are defined at the beginning of each period, and are assumed to vary linearly from the beginning of one period to the beginning of the next period.Evapotranspiration periods are contained in a table in the Evapotranspiration Window. If this window is not visible, display it by clicking the "Show" menu and selecting "Evapotranspiration Window". If this menu item is grayed out, you will have to first open the Model Options dialog box and select "simulate evaporation" and/or "simulate transpiration".
The columns of the table contains evapotranspiration parameters, which are divided into two panes:
Cells in the table are not directly editable. Instead, use the buttons below the table to:
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