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Research Papers

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

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Pages 177-189 | Published online: 23 Jan 2013
 

Abstract

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 19612002 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.

Les changements ventuels touchant les prcipitations extrmes au niveau local exigent des rvisions des rglements existants en matire de gestion de l'infrastructure de l'eau ainsi que des changements dans les pratiques de conception. La prsente communication value le changement dans les courbes IDF dont se sert la ville de London, en Ontario, dans des conditions climatiques changeantes. Un algorithme de gnrateur stochastique de conditions mtorologiques ou Weather Generator (WG) des k plus proches voisins, non paramtrique, est utilis afin de crer de manire synthtique des sries long terme de donnes mtorologiques. Neuf ensembles de donnes de prcipitations maximales quotidiennes (5, 10, 15, 30 minutes, 1, 2, 6, 12, et 24 heures), donnes recueillies la station de l'aroport de London pour la priode de 1961 2002, sont utiliss comme donnes d'entre pour le gnrateur. Le gnrateur fait appel des mcanismes perfectionns de rorganisation et de perturbation afin de gnrer des enregistrements synthtiques de prcipitations, semblables (mais non identiques) aux enregistrements historiques observs. Le mcanisme de rorganisation gnre des valeurs de prcipitations synthtiques et le mcanisme de perturbation peut gnrer des valeurs de prcipitations extrmes en dehors des limites observes afin de simuler des quantits de prcipitations futures plausibles non encore observes. Deux scnarios climatiques sont retenus pour l'analyse: la limite infrieure du changement climatique (LICC) et la limite suprieure du changement climatique (LSCC). Le scnario LICC fait appel des enregistrements observs en tant que donnes d'entre du gnrateur. Le scnario LSCC modifie l'enregistrement observ l'aide des rsultats d'un modle climatique mondial slectionn (les champs tant modifis) et utilise ensuite les ensembles de donnes de prcipitations modifis en tant que donnes d'entre du gnrateur. Les donnes de sortie servent gnrer les courbesIDF. Les rsultats de ltude comprennent la prsentation numrique et graphique des courbes IDF mises jour de 2, 5, 10, 25, 50, et 100 ans pour la ville de London, en Ontario. La comparaison entre les courbes IDF du scnario de changement climatique et les courbes IDF d'Environnement Canada fait tat d'une augmentation des intensits et de l'importance des prcipitations maximales, ce qui a des incidences majeures sur les diffrentes faons dont l'infrastructure actuelle (et future) de gestion des eaux municipales est conue, exploite et entretenue.

Acknowledgements

Financial support for the study provided by the City of London is greatly acknowledged. The authors would like to thank Mr. Adam Van Ymeren for programming support and Mr. Robert Morris and Mrs. Joan Klaassen of Environment Canada for providing assistance with the data.

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