Project teams using this tool assess the potential impact of climate and geophysical hazards on the physical components of their project for both types of flood defenses: built and natural. This potential impact is the combination of the exposure and sensitivity of the project’s physical assets, natural resources, and systems. Ratings of potential impact rely on the user’s subject matter expertise and contextual understanding.
Flood defenses: The flood defenses category is divided into two types: built (built infrastructure) and natural (coastal ecosystem). The nature of physical investments and associated potential impacts varies significantly between these two types. For built defenses such as sea walls and revetments, the impacts of climate and geophysical hazards tend to be physical: these defenses can be damaged by storm surge, strong winds, or earthquakes. By contrast, the natural defenses of the coastal ecosystem, such as mangroves, coral reefs, and marshes, may experience a reduced functionality of ecosystem services in addition to physical damage. For example, coral reef health can suffer from warmer ocean temperatures and higher acidity. Sea level rise can affect the ecosystem services of wetlands and marshes. Therefore, the potential impact ratings are separated into these two sets of impacts on flood defenses.
Evaluating historical trends: Potential impacts are evaluated separately for the Historical/Current and Future time-frames because the level of potential impact may change as exposure changes over time. It is important to first evaluate historical trends and current baselines to understand the conditions and trends under which coastal flood protection systems are currently operating. For example, the height of embankments may be based on a calculated period of recurrence of a certain storm surge height, based on historical records.
Rating future impact: After evaluating historical and current trends, users should map the projections for future climate onto the relevant time scale of their project components (see Figure 2), and rate Future potential impact on that basis. For investments with long lifetimes, such as physical infrastructure, considering future conditions is critical to avoid “locking in” designs that are not suited for higher sea levels or more intense tropical cyclones. For example, the effectiveness of a sea wall may be greatly reduced by sea level rise over time.
The potential impact is rated separately for each hazard, because both project sensitivity and impacts are specific to each type of hazard. For example, the height of sea walls and embankments is an important indicator of sensitivity to sea level rise and storm surge. However, sensitivity to earthquakes is a very different problem, because ground shaking challenges the integrity of structures differently than pressure from high waves.
The rating scale for potential impact looks like this:
|Insufficient Understanding||No Potential Impact||Low Potential Impact||Moderate Potential Impact||High Potential Impact|
In selecting these ratings, users overlay sensitivity considerations onto the previously determined exposure ratings to assess potential impact. Consequently, the potential impact ratings might or might not match the exposure ratings. For example, a certain coastal ecosystem might be highly exposed to strong winds that could cause erosion. However, the level of potential impact will also depend on the coast’s geology: rocky coasts are relatively insensitive to winds, but coasts that rely on natural defenses, such as sand dunes, are much more sensitive.1
1 See the Resource Annex. for a list of resources on the potential impacts of climate change for coastal flood protection.