Variables can be created based on imported data sets. This can be useful when simulating dynamics that relates to characteristics that can be derived from imported data (as opposed to relating directly to the imported data). For example, some plant species can tolerate brief inundation but become stressed or experience mortality when inundated for a long period of time. If a data set of “depth” was imported, a variable could be created for 30-day mean depths and later used in a rule that triggers stress and mortality for that plant species.
The Create Variables interface allows users to add, rename, copy, and delete variables. Variables are defined by name, time step, and statistical queries or a calculator equation. The example above could be handled with statistical queries. A variable called “long inundation” could be added and use the “depth” data set with statistical queries (duration of 30-days, mean) to compute a spatial and temporal variable. There are several statistical query settings that allow a mixture of duration and rate of change criteria to be applied. Calculator equations contain basic math operations (e.g., addition, subtraction, multiplication, division) and references to data sets, already defined variables, time series, paired data, and seasonal data (Figure).
Figure. Create Variables allows imported data to be used to compute variables for use in simulations.
Similar concepts can be built into rules. The advantage to using Create Variables is that the math needed to compute variable values are only dependent on imported data and can therefore be done before simulation, which lowers simulation run times.