[en] The 1.5D transport code JETTO (Cenacchi G. and Taroni A. 1988 Rapporto ENEA RT/TIB (88)5) has been applied to model the transition from the low (L) to the high confinement mode (H-mode) in the JET tokamak. Computed values of the critical power, P_th, required for the L-H transition on JET are directly compared with experiment (Andrew Y. et al 2006 Plasma Phys. Control. Fusion 48 479) across line averaged density and magnetic field scans. Reasonable agreement is found between computations and experiment across all densities considered, including low density discharges, where P_th increases with decreasing density. The minimum of P_th(n_e) dependence is explained by the enhanced contribution of the particle convection to heat losses at the edge. Higher convective losses result in lower temperature and its gradient, and therefore more power is required for the L-H transition. Computations performed for JET discharges with varied magnetic field show a rough agreement with the experiment, nonetheless both computed and experimental power thresholds are substantially higher than the inter-machine scaling predictions (ITPA H-mode Power Threshold Database Working Group Presented by Takizuka T. 2004 Plasma Phys. and Control. Fusion 46 A227, Snipes J.A. et al 2002 Proc. 19th Int. Conf. on Fusion Energy 2002 (Lyon, France, 2002))