Water Resources Research Report

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Summary

The climate is changing and these changes may induce severe impacts on both, global and local scales. The Public Infrastructure Engineering Vulnerability Committee (PIEVC) established by Engineers Canada conducted an assessment of the vulnerability of Canadian Public Infrastructure to changing climatic conditions. The major conclusion of the assessment is that water resources infrastructure failures due to the climate change will be common across Canada. As a follow up, the City of London took an initiative to evaluate the impacts of climate change on its municipal infrastructure. An original systematic procedure is used to gather and examine available data in order to develop an understanding of the relevant climate effects and their interactions with infrastructure. The key steps of the procedure include: (i) Inventory of infrastructure components; (ii) Data gathering and sufficiency; (iii) Qualitative vulnerability assessment; (iv) Quantitative vulnerability assessment; and (v) Prioritization of the infrastructure components based on the level of risk. The assessment work is based on the results of the previously completed climate change impact study and focuses on infrastructure vulnerability to flooding.

Assessment methodology requires identification of climate loading on the municipal infrastructure. Climate and hydrologic modeling methodology and results are presented in this report as the basis for the impact assessment work. A weather generator model combined with principle component analysis (WGPCA) and HEC-HMS hydrologic model are used in this study. The WG-PCA model is used to generate two different climate scenarios named: (a) historic scenario and (b) wet scenario, representing the lower and the upper bound of potential climate change, respectively. Generated meteorological data (precipitation and temperature) is used with the hydrologic model (HEC-HMS) and transformed into flow at multiple locations within the study region. Lastly, the flow frequency analysis is conducted to provide input into a hydraulic model that is used in mapping the floodplains for two climate scenarios considered (Sredojevic and Simonovic, 2009).

Using 43-years of historical data from 1964 to 2006 at 15 stations in the Upper Thames River basin, the WG-PCA generates a feasible future scenario of precipitation and temperature for 200 years – the historic climate scenario. The historic data is used to represent the business-as-usual condition that assumes there is no change in the social-economic-climatic system in the future. This scenario simulates climate change that may occur as a consequence of the already existing conditions and is considered in this study as the lower bound of climate change impact on the region under consideration. The second climate scenario employs CCSRNIES global climate model (GCM) with B21 emission scenario for time slice of 2040-2069 together with the historical data to generate a feasible future scenario we named in this work as a wet climate scenario – upper bound of climate change impact on the region under consideration. The results demonstrate the WG-PCA regenerates well the 25th, 50th, 75th percentile statistical values of precipitation and temperature for the historic scenario. Use of data perturbation process within the weather generator model generates data out of the range of values within the observed data. For the wet scenario, the WG-PCA generates the future that reflects the monthly climate shift of GCM model used (CCSRNIES B21) in the study.

The generated annual precipitation extreme values for 200 years are processed to extract the largest annual flood event for the entire basin and corresponding annual peak flow is used in flood frequency analysis. An assumption introduced in this work is that the largest floods are generated from extreme precipitation events. Several probability distributions including Gumbel, LP3, and GEV are utilized in this study. The flood frequency analysis results obtained using Gumbel distribution for the historic and the wet climate scenarios are compared with the current data used by the Upper Thames River Conservation Authority (UTRCA) for flood plain management. The difference exists between the current data and the data generated for two scenarios, as expected, and the direction of change varies with the location in the basin.

During the work on this study, the major deficiency in observed flow data is noticed across the basin – specially for the locations within the City of London. Therefore, continuous monitoring system at the various sites in the basin is needed to provide the accurate hydrologic information that should enhance the results of modeling work. If and when the new observed data is collected, the hydrologic modeling analysis can enhanced and consequently flood flow frequency analysis can be verified.

ISBN (Online)

978-0-7714-2845-6

ISBN (Print)

978-0-7714-2844-9

Publication Date

8-2009

Publisher

Department of Civil and Environmental Engineering, The University of Western Ontario

City

London, Ontario, Canada

Disciplines

Civil and Environmental Engineering

Notes

Report no.: 068

City of London: Vulnerability of Infrastructure to Climate Change

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