The role of susceptibility, exposure and vulnerability as drivers of flood disaster risk at the parish level

Fluvial flooding continues to be a process that has a major impact on society, the environment and the economy. Although its natural triggering factors, the spatial configuration of exposure and vulnerability is expected to play a relevant role in explaining the damage records. The starting point of this research is the use of existing flood susceptibility, exposure and social vulnerability mapping, produced at the parish level, as input data in a Classification and Regression Trees' (CART) model. Two models were ran, autonomously, that use two databases of flood damage as dependent variables: one including the human damages (fatalities, missing, injured, displaced and evacuated people) from flood events-the DISASTER database; another one that sums the DISASTER cases and the lower impact damages (damages to roads, railroads and buildings). The results show a quite distinct classification of parishes, whether one database is used or the other. The DISASTER database reveals susceptibility as the most relevant flood risk driver in explaining the damage patterns, while the database with all the flood cases identifies exposure as the more relevant driver. In the end, the degree of damages as documented in databases is conditioned by the geographical distribution and overlay configuration of the three flood risk drivers. Finally, the CART classification groups are analyzed at the light of the European Union's Floods Directive areas of significant potential flood risk. This analysis showed that the Directive's parishes are interpreted differently-in terms of their positioning in face of the risk drivers-which is explained by the use of distinct impacting-criteria in the construction of the flood damage databases.

Automated summary

This research used flood susceptibility, exposure, and social vulnerability mapping data as input for a CART model analysis. The results showed that susceptibility is the main flood risk driver according to the disaster database, while exposure is considered more important based on the database with all flood cases included.