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Flood vulnerability assessment of donstream area in Mono basin in Yoto district, south-eastern Togo

par Abravi Essenam KISSI
University of Lome - Master 2014

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2.4.1.Existing Flood Vulnerability Index

Connor and Hiroki (2005) presented a methodology to calculate a Flood Vulnerability Index (FVI) for river basins, using eleven indicators grouped into four components. The index uses two sub-indices for its computation: the human index, which corresponds to the social effects of floods; and the material one, which covers the economic effects of floods. The purpose of the FVI is to serve as a tool for assessing flood risks due to climate change in relation to underlying socio-economic conditions and management policies.

An elaborated methodology to calculate FVI was developed by Balica (2007), using indicators which aims at assessing the condition that favour flood damages at various levels: river basin, sub-catchments and urban area. The methodology focused on two concepts: factors of vulnerability based on three elements, including exposure, susceptibility and resilience on one hand, and components of vulnerability including actual flooding and establishing the elements of a system that suffer from this natural disaster on the other hand. The methodology has been applied at different scales and has resulted in interesting observations as to how quantifiable indicators can reflect backs. Balica defines vulnerability as a function of exposure, susceptibility, and resilience.

The Seventh Framework Programme (2011) defined the FVI in terms of the following factors: exposure, susceptibility, and lack of coping capacity. The methodology included a step of converting the indicators into non-dimensional units, by interpolating the maximum and minimum of the series of data obtained. The FVI values oscillate between 0 and 1, where 1 means the highest flood vulnerability and 0 represents the lowest vulnerability to floods. The methodology was tested in Japan river basins and in 18 river basins in Philippines.

Depending on the equation used, the indicators will have to have a different format, but the result of the FVI remains the same. The goal of the equation of the FVI is to compare different communes to one another in overall vulnerability, but also in its separate factors exposure, susceptibility and resilience. To make it possible to visualize these separated factors, a summation relationship is more useful. Also, it is preferred if the resilience is negatively formulated, and a higher score causes the vulnerability to be higher, conform other factors. With the chosen equation, the indicators have to be measured on a scale from 0-100% or 0-1, like Balica et al. (2012). Then, the indicators have to be normalised. The method of normalization has to take into account the functional relationship between the variable and vulnerability. If the functional relation is ignored and if the variables are normalized simply, the resulting index will be misleading. After computing the normalized scores the index is constructed by giving either equal weights to all indicators/components or unequal weights. These factors are then summed up according to the equation, and the result is a 0-100% or

0-1 number for vulnerability.

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