Rainfall Intensity Duration Frequency Curves Under Climate Change: City of London, Ontario, Canada

Potential shifts in extreme rainfall at the local level require revisions of existing water infrastructure management regulations as well as changes in design practices. This paper assesses the change in IDF curves for use by the City of London, Ontario under changing climatic conditions. A non-parametric K-Nearest Neighbour weather generator (WG) algorithm is used to synthetically create long time series of weather data. Nine daily maximum rainfall datasets (5, 10, 15, 30 minutes, 1, 2, 6, 12, and 24 hour) collected from the London Airport station for the period 1961-2002 are used as input into the WG. The WG uses sophisticated shuffling and perturbation mechanisms to generate synthetic rainfall records similar (but not identical) to the observed historic record. The shuffling mechanism generates synthetic rainfall values and the perturbation mechanism can generate extreme rainfall values outside the observed bounds to simulate plausible future rainfall amounts not yet observed. Two climate scenarios are selected for the analysis: climate change lower bound (CC_LB) and climate change upper bound (CC_UB). The CC_LB scenario uses observed rainfall record as WG input. The CC_UB scenario modifies the observed record using the results of a selected global climate model (change fields) and then uses the modified rainfall datasets as WG input. Outputs are used to generate IDF curves. Results of the study include numerical and graphical presentation of updated IDF curves for 2, 5, 10, 25, 50, and 100 years for the city of London, Ontario. The comparison between climate change scenario IDF curves and Environment Canada IDF curves indicates an increase in maximum rainfall intensities and magnitudes which has major implications on ways in which current (and future) municipal water management infrastructure is designed, operated, and maintained.