The lower Mekong basin is frequently affected by floods. Prolonged floods disrupt daily activities and cause huge socio-economic damage almost every year. An advanced flood warning system could provide achievable non-structural measures forreducing such damages. With a view to developing an advanced flood warning system, a distributed hydrodynamic modellingapproach has been adopted for simulating a flood inundation phenomenon in the lower Mekong basin. A modelling systemwith a one-dimensional (1-D) river flow model and a two-dimensional (2-D) surface flow model has been used for simulatingflood inundation. In the model, exchange of flows between the river and surface floodplain is calculated t hrough establishedlinks, which determine the overflow from river nodes to surface grids or v ice versa. These occur due to overtopping or failureof the levee when water height surpasses levee height. The model has incorporated detailed information about urban terrainfeatures like embankments, roads, bridges, culverts, etc. in the simulation. A geographical information system (GIS)-basedcomprehensive raster database of different spatial data layers is prepared and used in the model development. An explicitsolution scheme i s u sed for numerical computation, which considerably reduces the run time and makes the model suitable foruse as a flood warning system in a large river basin. The model simulated results in the lower Mekong basin have shown closealignment with the observed data in terms of water level and di scharge in various river gauging stations and flood extents inthe floodplain and from the results it can be inferred that the model can predict the magnitude and duration of flood inundationto a reasonable level of accuracy. Copyright 2007 John Wiley & Sons, Ltd