PLUS 4013-12

Introduction to this Guideline Water resources management infrastructures comprise one of the largest pools of capital stock owned and operated by municipal, provincial, and federal governments in Canada. In turn, every day Canadians rely on this infrastructure to help sustain their health and safety, protect their livelihoods, safeguard property, as well as to protect natural systems such as creeks, rivers, and lakes from environmental damage resulting from unintended discharge. In designing and managing these assets and systems, practicing professionals therefore need to be concerned with the probability of occurrence of extreme amounts of rainfall, often for specific storm durations, since these can result in extensive damage or disruption in services. Traditionally Canadians have relied on Environment Canada’s precipitation monitoring networks, sites, and derived climate (rainfall Intensity-Duration-Frequency (IDF)) information as the basis for the design, management, and operation of this critical infrastructure. Increasingly, however, the confluence of infrastructure deficits—resulting from aging assets plus the extension and intensification of Canada’s urban landscapes— and better scientific understandings of extreme rainfall patterns have raised concerns about the adequacy of IDF information for certain localities. Evidence that climate change will and may already be resulting in greater rainfall intensities across much of Canada has further amplified these concerns regarding the adequacy of “IDF coverage”. In reaction to the above dynamics, parties outside of Environment Canada have begun offering services for the provision of IDF information or, in the case of specific municipalities, have started to generate their own IDF information. In some instances, this has relied upon Environment Canada data with the generation of IDF information generally aligned with Environment Canada methodologies. In other cases, data may be used from other sources and methodologies may vary. The goal of this Guideline is therefore twofold. First, it seeks to provide the guidance necessary to ensure that the derivation and use of IDF information across all Canadian localities is as consistent and scientifically defensible as possible. Second, it provides some of the first formal evidence and advice for the incorporation of forward-looking information into IDF values and related design activities, such that the effects of climate change can be better considered. To achieve this goal, the Guideline seeks to: (a) Provide to practitioners a basic understanding of meteorological drivers of extreme rainfall that need to be understood so that practitioners can determine and meet their local needs; (b) Outline how IDF information has traditionally been developed in Canada, including explanations of the assumptions embedded within current IDF information that are of potential significance for water resources practitioners; (c) Provide guidance to determine if additional precipitation information, including IDF values, is required to optimize the local design of infrastructure; (d) If new IDF information is required, provide guidance for design and implementation of an enhanced precipitation network, including gauging needs and data requirements; (e) Discuss what the implications of climate change might be for the development, interpretation, and use of rainfall IDF information and provide guidance on how these implications could be considered; (f) Provide examples of how IDF is currently used in water resources infrastructure planning and design, outline best management practices for management of risks and sustainability and provide guidance on a range of adaptation options that address potential changes in rainfall IDF characteristics that could occur as a result of climate change; and (g) Highlight opportunities for expansion in future versions of the Guideline, including treatment of seasonal rainfall events, implications for measuring and monitoring and incorporation of rainfall data that meets variable standards for data quality, as well as additional resources on best practices for factoring in expected climate change implications for IDF information.