The potential impact from climate and geophysical hazards on the physical and structural components of the project is assessed for each hazard. This potential impact is the combination of exposure and sensitivity of physical assets, resources, and systems. The potential impact ratings rely on the user’s subject matter expertise and contextual understanding.
Evaluating historical trends: Users evaluate potential impacts 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 facing road systems today. For example, there may have been recent flood events that significantly exceeded the capacity of road drainage systems, causing widespread disruptions to traffic flow.
Rating future impact: Using the projections for future climate in that location and relating them to the relevant time scale (see Figure 2), users can focus on the aspects of their project that will be relevant to the outcome of the project in the Future time frame. Most road investments have long lifetimes, so considering future conditions is critical to avoid “locking in” designs that are not suited for higher sea levels or more frequent flooding. Coastal roads whose design is based on current sea levels, for example, may experience periodic or permanent inundation in several decades because the elevation is insufficient.
The potential impact assessment is rated against each hazard because the nature of sensitivity and impacts varies significantly among hazards. High temperatures may lead to pavement cracking, so the temperature rating of the pavement binder is an important indicator of sensitivity to temperature. On the other hand, sensitivity to heavy rainfall and flooding depends on the capacity of road drainage, including culverts, storm drains, and ditches, as well as road surface concerns. To capture these different sensitivities (and thus potential impacts), each hazard is rated separately.
The rating scale for potential impacts 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 with the previous exposure ratings to assess potential impact. Therefore, the potential impact ratings may or may not align with the exposure ratings. For example, a rural feeder road may only be occasionally exposed to heavy rainfall events. However, if it is unpaved, then the potential impact could be very severe due to high sensitivity. The Resource Annex provides a list of resources on the potential impacts of climate change on roads.