Volume.
ref_vol
Name of the physical variable: "volume".
Boxid starting from 0 to numboxes - 1.
Layerid starting from 0 to numlayers - 1.
Simulation time in years. Modeltimestep was converted to actual time based on the settings in the 'run.prm' file.
Obseravtion column storing the actual output value. Volume in m^3