The MAIN program is the portion of the science model which controls the initialization and execution of a WEPS simulation run. It calls subroutines that read
input data and outputs the general report. In addition, MAIN calls submodels on a daily basis, which update the field conditions. If the maximum wind speed
for the day exceeds a set velocity great enough to cause soil movement (i.e., 8 m/s), MAIN then calls the EROSION submodel to simulate erosion processes.
The current version of WEPS reads in the climate data produced by the WEATHER submodel; performs daily simulation of the hydrologic and soil conditions,
crop growth, and residue decomposition; and accounts for management effects. Finally, the model determines soil erosion by wind for the desired simulation period.
Program Description
The current version of MAIN requires the following files for a WEPS simulation run: a) a simulation run file which describes the field shape and barriers, simulation period, location of other input files, and types of output ; b) an initial field conditions file which describes soil conditions at the start of a simulation; d) a tillage/management file which describes the management system; and e) two climate files, one each in the CLIGEN and WINDGEN formats, that provide climate data on a daily basis.
The MAIN program begins by initializing local variables and then calls the subroutine INPUT which reads the simulation run file and the initial field conditions
file. The simulation then is executed as a daily loop that controls the counters for the current day and an embedded subregion loop. The model can perform any
length of simulation on a daily time step. However, WEPS performs a simulation for one rotation cycle to initialize surface conditions before simulations of
wind erosion are performed. For each simulation day, the daily weather is read from the CLIGEN and WINDGEN data files. As some of the submodels are
executed, summary information may be compiled for output. All submodels except EROSION are called within the subregion loop. Once field conditions are
updated, if maximum wind speed for the day exceeds a set minimum (i.e., 8 m/s), the EROSION submodel then is called to determine threshold conditions and
compute soil erosion. Finally, the MAIN program calls subroutine BOOKEEPING to account for field conditions and soil loss for periods throughout the
rotation. GENREP is then called, which outputs a series of user-selected output forms with general information about the simulation run.