Scenario-based Flood Risk Mapping

Overview

There is significant scientific evidence to confirm that anticipated changes in the climatic system are likely to influence future risks from a number of weather related hazards including floods. There exists a clear and direct relationship between global warming and changes in the precipitation patterns. With increasing temperatures, the water holding capacity of air will increase proportional (almost 7% increase for every increase in 1 deg. C) resulting in increased amount of water vapor in the atmosphere. Consequently, precipitation events that occur are very likely to produce more intense precipitation even in places where there may be a decrease in mean annual precipitation. This in turn increases the risk of flooding in most parts of the country. The problem is further magnified by decrease in snowfall, and increasing rates of snow melting during the next 50 years to global warming. Thus, it is reasonable to expect that there is a high likelihood of increasing risks from flooding events, which are presently not captured in the existing flood risk maps. Traditionally, to prevent flood damage the community of architects, planners and Homeland Security Enterprise (HSE) practitioners, have relied on historic flow information to determining flood frequency and magnitude, including the development of Flood Insurance Rate Maps (FIRMs).  These estimates have driven infrastructure design, building and repair, and have facilitated protected development in flood prone regions. However, changing climatic conditions are already starting to highlight the limitations of this approach. Traditional flood risk analysis assumes stationarity in flood magnitude and stage.  In terms of flood magnitude, it assumes that there is no long-term trend in the distribution of flood discharge over time. The 100-year (or 1%) flood in 1970 is the same as the 100-year flood in 2000 and is the same as the 100-year flood in 2030.  Stationarity also includes the assumption that changes in land cover/land use and development do not significantly alter flood stage. A number of researchers have questioned this assumption of stationarity with ongoing changes in climate, and land cover (Milly et al. 2008).  This sentiment is echoed by the National Research Council’s 2011 report Global Change and Extreme Hydrology: Testing Conventional Wisdom: “Assumptions on the occurrence of major hydrologic events to analyze extremes are based on the notion of stationarity, yet observational evidence increasingly shows that this assumption is untenable.”

This research project focuses on meeting the following operational needs of the HSE:

1. Providing timely, accurate and actionable risk information to guide future infrastructure development and management decisions;
2. Determine tolerable levels of risk with respect to various community infrastructure assets (for example a trauma care facility versus an electric sub-station); Allow for realistic cost-benefit analysis of future investments;
3. Identify future needs for undertaking actions and measures that enhance resilience prior to any extreme hazard event;
4. Formulate emergency response and training scenarios based on the enhanced assessment of flooding risks, so that they are not caught off guard by extreme hazard events;
5. Coordinate with other owners, operators, and stakeholders to build networked capacities that will minimize local infrastructure failures and avoid cascading effects.