Running a Century Simulation to Equilibrium

Running the Simulation

Commonly a simulation will take 2000 to 4000 simulation years to reach a state at which the soil organic C pools are approximately at steady state. Examine particular output variables for equilibrium conditions. We recommend looking at SOM2C and/or SOMTC. The fast C pools and the N pools often change too quickly and may oscillate, and are more sensitive to precipitation and temperature. At equilibrium the value of the representative output variable should change little with time.

When selecting the output variable to examine for equilibrium, consider your time frame and management schedule. For example, a natural grassland without disturbance should show steady state pools amounts on an annual output interval. If your management schedule has events on a multi-year cycle, e.g., alternating crop and fallow with regular cycles of fertilization and harvest, then monthly and annual intervals will reflect the effects of management. In this case, examine output variables over multiple management periods for an approximate steady state.

Usually the main purpose of running a simulation to equilibrium is to achieve soil pool values that will be used for a new site file as the basis of your simulation experiments. Obtaining an equilibrium state for a natural grassland, for instance, provides the basis for examining the response of the system to disturbance. Century5 can create a new site file at the end of a simulation using the -sf command-line option. See Running Century and CMI with Command-Line Options for details.


To run a simulation such that model reaches equilibrium, consider the following factors which will influence the model state.


If the equilibrium value for SOM2C or SOMTC does not approximate the expected value for the site the first thing to check is the NPP value (variable CPRODA ). If NPP is too high or too low none of the other output variables for the simulation can be expected to be representative of the site. The reasons for too much or too little NPP include

See Also

Running Century and CMI with Command-Line Options
Editing Site Parameters
Site Parameters Validation