I’m seeing the same pixels experience high severity, mixed severity, and low severity wildfire in one time step. It seems that contagion can cause a given pixel to experience all three in one year. Is that right? The model doesn’t know that a given pixel may have already experienced wildfire in a given time step when spreading a different fire event from some other starting point? If that’s the case, which fire is recorded as the one that disturbed the area in the summary output? Or, maybe the pixel is recorded as having burned three times…which may not make much sense….
The main reason why you would observe different fire types occuring to the same cell in the same timestep is if those fire types are in different primary transition groups. These primary transition groups define the set of transitions that will be simulated as a unit within the model. Transitions belonging to the same primary group can be part of the same transition event and can’t occur more than once to an individual cell in a timestep. My guess is that in your project definitions for transitions you have currently either assigned a different primary group for the three different kinds of fire, or you have not defined primary groups at all, in which case all transition groups are considered primary. If it is important for you that the different fire types belong to different primary groups, you could prevent multiple occurences in one timestep by setting a minimum TST since fire for each of these fire types. Finally, if multiple fires occur to a pixel within a timestep, all types will be recorded in the cummulative area burned.