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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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4.3.4. Composite vulnerability index of vulnerability factors

4.3.4.1. Exposure factor

Exposure considers the indicators which explain how social entities such as households or economic activities like agriculture, etc., are exposed to flood events. Ten (10) indicators are used to explain the determinant of communities' vulnerability to flood disaster under exposure factor. Two main determinants are found: flood characteristics composed of flood frequency, magnitude, depth and duration as well as elements at risks composed of households and their farmland. Flood characteristics are quite the same for all the surveyed village but the difference is related to the elements at risk in each village. The composite vulnerability index of this factor is calculated for each village. By considering the composite index of exposure factor, the most exposed villages are Djrekpon and Kpodji with high indices ranging from 0.0451 to 0.0651 "Map 3". The most exposed villages have the highest scores for most of the considered indicators under the elements at risk compared to the other villages : high population and farmland in flooded area, high percentage of women and children and elderly in flooded area "annexe 6".

Map 3: Flood Exposure map of the study area

4.3.4.2 Susceptibility Factor

Susceptibility considers the indicators which evaluate the sensitivity of an element at risk before and during a flood event. Eleven (11) indicators are also equally used to explain the determinants of communities' vulnerability to flood disasters under susceptibility factors. The composite index of susceptibility factor for each village is computed. By considering the composite index of susceptibility factor, the most susceptible villages are Batoe and Atikpatafo with high indices ranging from 0.0058 to0.0065 "Map 4". The most susceptible villages have the highest scores for most of the considered indicators :high female headed household, low education level, limited livelihood strategies, high household size, low coping capability, low access to emergency service, low preparedness capability "annexe 6".

Map 4: Flood Susceptibility Map of the study area

4.3.4.3 Resilience Factor

Resilience factor considers indicators which clarify the ability of a Human-Environment system to persist if exposed to flood by recovering during and after the event. Eight (08) indicators have been used to explain the determinants of communities' vulnerability to flood disasters under resilience factor. The composite index of susceptibility factor for each village is computed. By considering the composite index of resilience factor, the least resilient villages are Djrekpon, Tchakponou and Kpodji with indices ranging from (0.0059- 0.0069 ) "Map 5". The least resilient villages have the lowest scores for most of the considered indicators :Low knowledge on warning system, low evacuation capability, low recovery capacity "annexe 6".

Map 5: Flood resilience map of the study area

4. Composite vulnerability index of components

The values of the indicators were used in the following general equation of vulnerability to determine the overall flood vulnerability index. Among the eight villages surveyed, Djrekpon and Kpodji are found to experience relatively high vulnerability with indices ranging from (0.0048-0.0225) , Batoe, Atikpatafo, Logokpo and Tchakponou are found to be moderately vulnerable with indices ranging from (0.0256-0.461) and Mawussou and Tofacope are estimated to suffer relatively low level of vulnerability to flood disaster with indices ranging from (0.462-0.668) "Map 6".

Map 6 Flood vulnerability map of the study area

This section compares the vulnerability of the selected villages by computing the composite vulnerability index of the three factors of vulnerability, using indicators identified under the different determinants of Human-Environment system and the overall flood vulnerability index. The overall FVI has shown two most vulnerable villages: Djrekpon and Kpodji. It is found that Djrekpon and Kpodji villages were highly exposed, Djrekpon was highly susceptible and Kpodji was moderately susceptible while the two villages were found to be least resilient. Some justification can be found in these results by looking at the number of households affected by floods during the last ten years, the high percentage of household heads with no education level, the lack of livelihood strategies option of those households, the highly susceptible building materials, the lack of adequate coping capacity and recovery capacity from floods. However, the low values found in the different results of the three factors of flood vulnerability as well as in the overall vulnerability index for some villages can be misinterpreted as not being vulnerable to floods. This may not be the case since all determinants of human-environment or socio-ecological system can be damaged under certain conditions.

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