Flood Risk Mapping - Methodological Guide

The ‘Flood Risk Mapping - Methodological Guide’ has been developed within the research project "Flood Risk and Vulnerability Mapping in Climate Change Scenarios" (CIRAC) in partnership with the Portuguese Association of Insurers and the research group Climate Change Impacts Adaptation and Modelling (CCIAM), Faculty of Sciences University of Lisbon, and is part of a PhD thesis in progress with the interim title "Climate change, flooding and the city. Contributions to the study of urban resilience in situations of torrential rain."

The results of the hydrological modeling presented in this paper were also obtained under CIRAC project, a partnership between the company Action Modulers S.A and CCIAM using an integrated version of MOHID Land and Storm Water Management Model software.

The purpose of methodological guide consists of presenting a methodology that allows quantifying the risk of flooding associated with the built environment embodied in buildings. There are, however, specificities that will determine the methods of analysis, namely the size of the basin and the type of flooding that occurs there. Not being able to treat all cases, the approach presented here focuses on flash floods in small basins. The proposed method can be used to assess the risk of flood in climate change scenarios. However and due to the complexity of the necessary procedures to obtain data from extreme rainfall resulting from models that perform these scenarios, it was decided not to include this process in this guide.

The first part of this paper is dedicated to the main concepts related to the evaluation of flood risk, whose domain is critical for understanding the remaining content of the paper. 

The second part presents the methodological procedures for the assessment of flood risk. This assessment starts with the necessary processes for defining probabilities of occurrence associated with the phenomena of flooding and then addressing strategies aimed at optimizing the hydrodynamic modeling to obtain flooded areas and other characteristics of the flood.

Finally we propose a method to quantify flood risk based on the annual average damage for different damage categories. In this last part it is also proposed to integrate the different damage categories in a single indicator with the purpose to conduct a comprehensive reading of the risk that a particular area is exposed to.