Projected changes in the future rainfall of the Sydney metropolitan region were investigated through fine scale (2km grid) dynamical downscaling from a single global climate model (GCM) simulation using the Weather Research and Forecasting (WRF) regional climate model. Projections of rainfall (2040-2059) were compared with a reanalysis-driven simulation for the period 1990-2009. There are projected to be changes in rainfall throughout the region with substantial temporal and spatial variation. The primary mechanisms for these changes were investigated using daily and monthly model outputs. Increased autumn rainfall is primarily caused by greater frequency and intensity of heavy rainfall events during some years. The increased intensity of these rainfall events may be due to greater availability of moisture from the tropics and the interaction between tropical and sub-tropical systems. The influence of the local topography on rainfall patterns is also evident at this scale. However the seasonal variation of change in rainfall is mainly determined by the outer domain and boundary conditions.