Design Criteria of Urban Drainage Infrastructures under Climate Change

Actual projections provided by climate models suggest that the probability of occurrence of intense rainfall will increase in a future climate due to increasing concentrations of greenhouse gases. Considering that the design of urban drainage systems is based on statistical analysis of past events, an increase in the intensity and frequency of extreme rainfall events will most probably result in more frequent flooding. The design criteria must therefore be revised to take into consideration possible changes induced by climate change. A procedure is proposed to revise the design criteria of urban drainage infrastructures. This procedure integrates information about (1) climate projections for extreme rainfall over the region under consideration; (2) expected level of performance (or acceptable level of risk); and (3) expected lifetime of the infrastructure/system. The resulting design criterion ensures that the service level remains above the selected "acceptable" level over a predefined portion of the infrastructure lifetime. It is argued that the definition of new design criteria should be part of a global adaptation strategy combining various measures to maintain an acceptable level of service in a long-term perspective. Defining this level of service is however a challenge in a context where uncertainties on projected changes in intense rainfall are still important.