Managing Assumptions in Climate Risk Assessments Using Assumption-Based Planning

Making assumptions is inevitable when performing any risk assessment, especially when it comes to climate risk. Assumptions can be conceptualised as assertions that are taken for granted, and in climate risk assessments, these may relate to models, data, scenarios and risk follow-up. The assumptions need to remain valid for the duration of the activity that the risk assessment concerns. In general, there is uncertainty about whether an assumption will remain valid in the future, and if it is not valid, this may have consequences. Making assumptions thus introduces a type of risk that has been labelled as assumption deviation risk. An option to avoid this type of risk is to conduct an uncertainty assessment with respect to the future state or condition that the assumption concerns. In practice, this quickly becomes infeasible for the large number of assumptions that are typically made in climate risk assessments and, in fact, in any risk assessment. We apply an alternative approach to manage the assumption deviation risk by monitoring the assumptions as time proceeds and implementing various strategies to control existing and emergent uncertainties. The approach is based on the assumption-based planning framework. In the present paper, we apply this previously proposed framework for establishing such strategies to climate risk with a focus on just one instance: flooding risks resulting from a changing climate. Our preliminary findings indicate that assumptions are not adequately treated in flood risk assessments, making it difficult to know how assessments are affected when changes happen or new knowledge becomes available.

Keywords: Assumptions, Assumption-based planning, Climate risk.