Critical review of the evolution of the design storm event concept

A critical review of the literature and practice indicates that design storm events, which have been used in specific fields of Canadian and US engineering practice for more than 100 years, can be ascribed to six basic attributes: (a) design return period, (b) storm duration, (c) intensity–duration–frequency (idf) relations (representing a summary of historical rainfall data, with some extrapolation for longer return periods), (d) temporal distribution (design hyetograph), (e) areal reduction factor, and (f) antecedent moisture conditions. Concerns about climate change (or variability) and the need to adapt to the associated climatic conditions prompted many agencies, and particularly municipalities, to revisit the design storm event issue, particularly in connection with drainage design. It would appear that this analysis has mostly focused on a single property of design storms — idf relations and projected increases in rainfall intensities. The review concludes that the design practice would be well served by adopting a comprehensive approach considering all design storm event characteristics and their sensitivity to climate change and inherent uncertainties in the existing idf relations as well as hydraulic design of sewer networks.