Scientists have made several attempts to evaluate the climate change impact on flooding all over the world. Flood studies have been carried out using the results from coarser resolution Global Circulation Models (GCMs). As the resolutions of GCMs are too coarse, the results of GCMs should not be directly used in the catchment scale hydrological modelling for accurate estimation of rainfall. Therefore the outputs from GCMs need to be downscaled to provide climate simulations at appropriate temporal and spatial scales.The output of the hydrological model presents runoff which is used as an input to the hydraulic model. One dimensional (1-D) hydraulic modelling is the traditional approach to simulate river channel flows, because it is computationally efficient to deal with complex and large river systems and large hydraulic structures. However, 2-D models are more suitable for floodplain flows where more accurate physical and hydrodynamic conditions are important. This paper will review the importance of downscaling and different downscaling techniques as well as their relative strength and weakness. This paper will also discuss the relative advantage and disadvantage of 1-D and 2-D hydraulic models for flood studies.