Hydroinformatics found its origin in the advancement of computational hydraulics in the early 1990s but has expanded considerably, both in scope and in application areas. It is now not only being applied in the fields of hydraulics and hydrology (often indicated by the colour blue), but also in environmental science and technology (green) as well as in knowledge systems and knowledge management (yellow). This paper focuses on urban (red) applications of hydroinformatics, taking urban flood and disaster management as an example. It is part of a sequence of papers, each focusing on a particular field (colour) of hydroinformatics, which together constitute a multi-coloured rainbow of application areas that hydroinformatics has expanded into over the past two decades or so. The combined papers on “Hydroinformatics in multi-colours” were presented as the opening keynote of the Workshop on Advances in Hydroinformatics held in Niagara Falls, in June 2007. In this paper—part red of the sequence—the role of urban hydroinformatics in assessing effects of climate change on urban flooding and health risk is addressed in relation to the UN Millennium Development Goals and illustrated on a case study of Dhaka, Bangladesh.