An indexing approach to assess flood vulnerability in the western coastal cities of Mazandaran, Iran

River flooding is a common natural disaster in the southern coastal strip of the Caspian Sea and is of great concern in cities in which the flood risk, mostly due to the high level of vulnerability, is significant. The principle aim of this study is to invent an indexing method for the assessment of vulnerability toward floods in the western coastal cities of Mazandaran Province, Iran. The developed indexing method assesses the vulnerability through identification and evaluation of effective criteria by scoring technique. These criteria are categorized into three indices (technical, socio-economic and population-environmental ones) and cover the factors of vulnerability toward floods, i.e. exposure, susceptibility and resilience. The method defines the flood vulnerability by a quantitative magnitude called relative vulnerability score and results in the vulnerability zoning of the area under assessment. The method was applied in Nowshahr (a city in Mazandaran) and the obtained results showed that: (1) the indexing method leads to a relative sense and an overall picture of the urban vulnerability toward floods, (2) the urban zones surrounded by two rivers, are in danger of a high level of the vulnerability, especially the first floors of the buildings, (3) it is necessary to review the location of the parking garage under construction, with regard to the flood vulnerability zoning. The flood vulnerability zoning was found to be in a good agreement with data obtained from field observation the flood that happened in Nowshahr in 2011 in terms of the damage.