Development and application of a systematic approach for prioritising the risk of failure of stormwater control strategies within selected SWITCH demonstration cities

A key objective of SWITCH is to support Learning Alliances (LAs) in the development of integrated urban water management strategies. Theme 2 of the SWITCH project is focused around sustainable stormwater management and its interactions with other sectors of the urban water cycle (e.g. water supply, eco-sanitation and urban agriculture) with a particular emphasis on achieving a paradigm shift whereby stormwater is regarded as a resource rather than a wastewater. The development of a sustainable urban water management strategy is recognised as a complex challenge, not least because it should consider both current as well as the future needs and challenges posed by the ‘city of the future’. To support LAs in tackling this challenge, representatives of LAs in Accra, Birmingham, Belo Horizonte and Hamburg were involved in discussions directed at the identification of city-specific threats and uncertainties which may result in the failure of their existing stormwater management strategies over both the short-term (time period of 5-10 years) and the long-term (time period of 25-30 years). Following collection of this data, a procedure has been proposed for assessing the consequences (severity) of an identified threat occurring together with an identification of its likelihood (probability) of occurrence (i.e. the translation of hazard into risk). To facilitate the involvement of LAs in this process, a series of guidelines have been developed to support the consistent assessment of risks through the adoption of a risk-rating approach. This procedure involves the development of ‘risk scores’ which can be utilised to prioritise, or rank, identified risks, thus providing a framework for the further consideration of how such risks may be managed within the development of long-term planning policies. This paper presents the theoretical elements behind the risk-rating methodology, which has been developed and describes the approach taken with regard to ‘benchmarking’ the concepts of severity and probability in relation to stormwater control in densely urbanised areas and by specific reference to the Belo Horizonte and Birmingham demonstration cities.