Modelling hazard interactions and cascading impacts; development of the RiskChanges tool

Disaster events are often generated by a combination of factors, related to the occurrence of multiple hazards in space and time, leading to direct and indirect impacts in different sectors. Impact chains have proven to be a useful tool for understanding and visualising the sequence of impacts of such events. They are generally co-developed with stakeholders in workshops and may result in rather complex networks. Whereas these are very useful for understanding past events, their application to forward prediction, and the quantification of the various interactions and impacts, remains a major challenge.

The RiskChanges tool was developed to assess the impact of multi-hazards at a local level, especially for hazardous events that have a high spatial variation. The tool can be used to compare the current level of risk with those in future years, following climate change and urban growth scenarios. However, the impacts of individual hazards were still assessed individually and combined in the risk assessment phase.

Now we have further developed the tool, and have considered the possibility of multi-hazard exposure analysis, combining two or more hazardous events. This can be done using multi-hazard modelling (e.g. for landslides and flooding under extreme rainfall events), or by assessing the exposure to two hazards together.  After this, simple impact chains can be built to determine how physical vulnerability and exposure are linked to assess the losses of consecutive, concurrent, and cascading events, for different types of elements at risk.  

The tool offers a simple and useful tool to estimate the impacts of complex events and to improve preparedness planning and impact-based forecasting. An example of the application of the tool is presented for volcanic and hydrometeorological hazard interactions for the island of Saint Vincent in the Caribbean.