Introducing Risk Assessment: Defining Standards, Selecting Measures, Working with Nature
Historically, efforts to manage floods often focused on controlling flood hazards. Physical infrastructure measures engineered to meet certain design standards and levels of protection promoted a sense of safety sometimes disconnected from what was being protected, the degree of flood preparedness, changes over time, uncertainties, and hazards from flood events greater than the design flood. Recently, governments are increasingly emphasizing the broader concept of flood risk management. Flood risk management seeks to address the probability of occurrence of a flood hazard, the vulnerability of flood mitigation from a broad variety of measures implemented to lessen flood consequences, and the consequences that result from the mitigated hazard, all within a wider context that recognizes such things as environmental function and social factors. In order to manage flood risks, we must first be able to asses them: to identify, measure, and determine the uncertainties associated with a range of flood hazards, vulnerabilities, and consequences.
The broadened scope and the acknowledged uncertainties make such assessment challenging. Local effects of climate change and land use change affecting the flood hazard need to be identified and carried forward through time with consequent adjustments to flood hazard probabilities. Vulnerabilities of mitigation measures need to be catalogued and quantified in a probabilistic sense (to include such things as the risk of geotechnical failure for earthen structures, the probability of successful implementation of evacuation plans, and consideration of the possible growing risk over time posed by aging infrastructure). Consequences of flooding include consideration of changing demographics—not only of total population at risk, but also the nature of that risk, to include anticipated development trends and social vulnerabilities. Consequences encompass changes to individual risk to societal risk, to investments in infrastructure, and to environmental systems.
Some countries are considering defining standards that could set goals or mandates in place regarding tolerable levels of risk. Others are striving to create coherent information about a wide variety of probable scenarios and outcomes over time, so that policy makers can make risk-informed decisions within societal and fiscal constraints. This session explored current practices in identifying and defining flood risks, measuring its various aspects, and presenting that information so that meaningful decisions can be taken with respect to flood risks and within broader environmental and societal contexts.
revised 18 Feb 2011