The gas diffusion layers (GDL) are crucial components as regards the water management in proton exchange membrane fuel cells. The present work aims at clarifying the mechanisms of water transport in GDL on the cathode side using pore network simulations. Various transport scenarios are considered from pure diffusive transport in gaseous phase to transport in liquid phase with or without liquid-vapor phase change. A somewhat novel aspect lies in the consideration of condensation and evaporation processes in the presence of a temperature gradient across the GDL. The effect of thermal gradient was overlooked in previous works. The temperature gradient notably leads to the possibility of condensation because of the existence of a colder zone on the channel side. The pore network simulations lead to phase distributions in qualitative agreement with X-Ray tomography visualizations. The simulations also indicate that the probability of GDL water flooding increases with the distance from the bipolar plate channel inlet.