A three-dimensional city model based on public accessible online information has been developed with success in this study. Detailed procedures on how to develop such model for computational fluid dynamics (CFD) simulation by using online maps, public accessible building information and online multimedia data will be reported in this paper. The city model developed in this study covers Marina Bay area of Singapore that includes highly developed urban region with many skyscrapers, greenery and water bodies, making it suitable for future urban heat island investigation. It can predict the street-level wind climate with a resolution of meters and has been validated by comparing with the measured wind data. We then conduct a risk assessment study of urban wind channels caused by a tropical typhoon, Vamei, which passed by Singapore on 27th Dec 2001. Furthermore, the application of the CFD city model in improving a real time wind prediction system for water quality control purpose is discussed.