Multivariate Flood Risk Assessment of the Unplanned Semi- Urban Region by Incorporating Flood Hazard, Vulnerability, and Exposure

Abstract

The mapping of flood risk is important to identify areas at risk and to improve flood disaster management and preparedness. Flood risk is often expressed as the product of the hazard and the probable consequences which is determined in terms of direct damages by assessing flood vulnerability and exposure. This study aims to develop the flood risk assessment (FRA) framework for the dense semi-urban region by incorporating flood hazard, topographic and socio-economic vulnerability, along with exposure, which is calculated by considering housing conditions and classification of the damages by different land use and land cover classes. The FRA at the municipal level is challenging due to the spatial resolution of social, economic, and medical indicators therefore this study attempts to map the flood risk of the semi-urban region where the different zones and housing communities are intertwined due to a lack of town planning. This FRA framework is applied to the Kulgoan-Badlapur Municipal Council (KBMC) located at the Ulhas Riverbank, a west-flowing river in Maharashtra, India. The city is located at the riverbank, which receives more than 2000 mm rainfall annually, and as most growing industries and businesses depend on the river itself, the risk associated with flood increases exponentially. The study shows that the spatial distribution of the flood risk is higher in the wards which are densely populated and near the river stream. Despite low population and assets, some neighborhoods are highly susceptible to flood due to their topographical conditions. Over the years, the population has been increasing in the neighborhoods due to the new real estate projects, which will make them more vulnerable to floods, and the overall risk is increasing. Study shows that the 82% of the area of Valavli and Manjarli ward comes under high flood risk due to high topographic vulnerability and exposure. Similarly the few parts of Industrial zone also comes under the high risk because of its location near river bank. The wards like Kulgaon comes under medium flood risk despite its high socio-economic vulnerability and high exposure which proves that the flood risk is majorly depends on the flood inundation. The exposure-based flood risk assessment will help to frame a more practical and reasonable evaluation of risk for growing urban and industrial zones.

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Tables

Table 1. The pairwise comparison matrix of the topographic parameters.

Table 2.  Normalized weightage calculated based on the pairwise comparision. 

 Table 3. Sub-criteria pairwise comparison matrix and weightage 

Table 4. Degree of importance for different land use and zones