Urban drainage and climate change: review of potential impacts and potential means for adaptation

Hydrologic design of urban drainage networks is based on statistical analyses of available historical meteorological data, assuming that a design rainfall event of a specific return period will produce runoff parameters (volume and peak discharge) with the same return period. The relevant design information for rainfall is usually synthesized in Intensity-Duration-Frequency (IDF) curves which present, based on past data, the rainfall intensities for different durations and frequencies of occurrence; the development of IDF curves is closely associated with the use of the rational method since the early 1900s and is also used to derive synthetic design storms.

It is however generally recognized that climate change (CC) could modify relevant design parameters like the extreme rainfall intensities and recurrences, these changes increasing in turn the probability that the design capacities of sewer networks be exceeded. In some cases, this situation could have significant impacts leading potentially to increased urban surfaces or basement floodings, overflow of detention basins and increased combined sewer overflows.

A review is made first of the approaches used so far to evaluate the impacts CC could have on relevant parameters for urban drainage design and of previous studies in Canada that have striven to quantify these impacts for practical purposes. The methodology that has been used to evaluate, for the Montréal area, the potential impacts of climate change on the meteorological design parameters for urban drainage systems is then presented, with an evaluation of the associated impacts on the runoff volumes and peak discharges for typical urban land uses. Finally, the potential means of adaptation that could be used to compensate for these changes so that the systems could still provide the adequate level of service is discussed.