The invention relates to systems and associated methods of operating fuel cell systems where the rotational speed of a reactant humidification enthalpy wheel is dynamically controlled according to various process variables. In one embodiment, a method is provided for operating a fuel cell system, including the following steps: (1) rotating a porous desiccant material about a rotational axis; (2) flowing air through the desiccant material in a direction parallel to the rotational axis to a cathode inlet of a fuel cell; (3) flowing cathode exhaust from the fuel cell through the desiccant material; (4) monitoring a process performance variable; (5) detecting a change in a value of the process performance variable; and (6) varying a rotational speed of the desiccant material in response to the detected change in the value of the process performance variable.