The transport of tungsten vapour evaporated from the electrode surfaces of a high-pressure xenon short-arc lamp, which is dominated by the gas convection in the lamp, determines the location and extent of the blackened area on the inner bulb wall. We have investigated factors affecting the vapour transport and other important phenomena related to the gas convection using a unified numerical model. The influence of the lamp operating parameters and also the thermodynamic and transport properties of the gas is discussed. The predicted lamp characteristics and phenomena agree well with experimental results. The gas velocity in the lamp is strongly affected by the Lorentz force and the gas density, which respectively depend on the current and the filling pressure. The viscosity and density of the gas adjacent to the anode surface were found to depend on the anode energy balance and to affect the resistance of the gas flow, which in turn affects the separation point of the gas flow from the anode surface. This indicates that the anode surface temperature, which is determined by the energy balance between the gas and the anode, also affects the blackening location.