11 Assessing climate risks
The aim of this step is to refine the previous analyses in order to identify and prioritize the hazard-system-impact sequences with the greatest risks, which will be used in subsequent analyses. A system or its components are at risk if they are exposed and vulnerable to a hazard. Risk assessment involves three steps: (1) risk identification; (2) risk analysis; (3) risk evaluation.
Risk identification
The goal of risk identification is to precisely identify and evaluate the risks associated with each hazard-system-impact combination based on climate information, vulnerabilities and potential consequences in current and future climates. This step is divided into three sub-steps.
Identification of systems and components: done by reviewing the lists of potential impacts for each hazard-system combination1 and assessing whether each of these hazards can affect each system, thereby identifying the hazard-system pairs to consider in the next steps. At this stage, the impacts identified remain generic and need to be contextualized as part of the risk analysis.
Vulnerability analysis: aims to determine the propensity or predisposition of a system to be negatively affected. This is an optional step, but performing the vulnerability analysis can be very useful in determining the consequences during the risk analysis (11.2). An example of a vulnerability analysis is given in Fact Sheet 14.
Exposure analysis: allows you to establish whether the system is actually exposed to each hazard. A system could theoretically be impacted by the hazard, but may not be exposed to it in the specific context being considered, in which case it would not be included. At first, this analysis can simply be limited to determining whether the element is or is not exposed (a yes/no type of analysis). The list of systems at risk in past and future climates can be established in this way.
Risk analysis
A risk analysis involves assigning a risk level to each hazard-system combination. The risk level (R) is defined as the product of the likelihood of the hazard (L) and its consequences (C) on the system or its components, written as \(R = L C\) (Fact Sheet 13). A risk matrix is created for each hazard-system combination by considering all the impacts of this hazard on this system. The climate thresholds identified in the previous step (Fact Sheet 10) can be used to assess the risks associated with exceeding these thresholds. Several thresholds may also be considered in order to assess the risks of hazards of different magnitudes.
Risk evaluation
The values obtained during the risk analysis make it possible to establish a risk level and to identify and prioritize the components or systems most at risk from a given hazard. The hazard-system combinations involving major and extreme risks must be prioritized (see Fact Sheet 13). Once this analysis has been carried out for each hazard-system combination, that provides a risk evaluation based on two future horizons and at least two SSPs. Generally, the risks will be greater the further away the future horizon is and the greater the . Table 11.1 presents an example summary of the results of the risk assessment step for different hazard-system-impact combinations. This table shows that floods caused by extreme rainfall pose the greatest risks for the time horizon 2071–2100.
| Hazard-system-impact | Reference period | 2041–2070 | 2071–2100 | ||
|---|---|---|---|---|---|
| SSP2-4.5 | SSP3-7.0 | SSP2-4.5 | SSP3-7.0 | ||
| Damage to buildings from sewer backups caused by extreme rainfall | Moderate | Moderate | Major | Major | Extreme |
| Mortality and morbidity in the elderly population following heat waves | Negligible | Minor | Minor | Minor | Major |
| Road surface degradation caused by freeze-thaw cycles | Minor | Minor | Major | Major | Major |