In April 2003 the UK Engineering and Physical Sciences Research Council (EPSRC) and a diverse group of interested partiesbegan funding a number of major projects looking at the impacts of climate change on the built environment, transport and utilities.One of these projects, entitled AUDACIOUS, is concerned with the impact of climate change on all aspects of urban drainagesystems. The main objective of this project is to investigate key aspects of the effects of climate change on existing drainage in urbanareas, and hence provide tools for drainage managers and operators to adapt to uncertain future scenarios. A major element of thiswork is the development of a set of numerical models to simulate the performance of urban drainage systems under the type ofextreme rainfall events associated with climate change. Once developed, it is intended to utilise such models in a diagnostic designcapacity, to assist in the formulation of strategies to improve the performance of new and existing urban drainage systems underdifferent climate change scenarios. This paper details the work that has been undertaken at Heriot-Watt University as part of theAUDACIOUS project. To date, this has involved the development of a numerical model to simulate the performance of roofdrainage systems (both conventional and siphonic) under extreme rainfall events. The necessary experimental work is described, andthe development of the model is detailed. Comparisons between model output and laboratory data are illustrated. Finally,conclusions are drawn regarding the progress to date, and plans for the next stage of the project are outlined.r2005 Elsevier Ltd. All rights reserved