Flood hazards are expected to occur more severely and frequently because of the effects of climate change. As a result, many areas in the world are facing the serious threat of flood hazards. Unplanned or poorly planned urbanization, rapid conversion in land use, and fragile flood management are some of the factors contributing to adverse flood effects which would lead to escalating risks for the inhabitants (Nasiri et al. 2016). This paper argues flood vulnerability assessment as the vital part of urban flood management. During the International Decade of Natural Disaster Reduction (IDNDR) from 1990 to 1999, it was recognized that the earlier concept of “flood protection” was inappropriate (UNISDR 2009). There cannot be complete protection, which is inaccessible and cannot be sustained, due to very high costs and inherent unpredictability. Flood management has been suggested as a realistic alternative, because it is more applicable and this concept is now being increasingly accepted and practiced in environmental studies. Flood risk management encompasses a wide group of subjects and tasks extending from the forecasting the risk, their social implications to methods and tools to minimize risks and economic costs and loss of human lives to adequate and acceptable levels. Avoiding, decreasing or shifting the effects of flood for mitigation and adaptation is the primary objective of flood risk management (UNISDR 2009). Two approaches exist in facing flood: structural (flood protection) and non-structural measures. Structural measures involve expanding the infrastructure like levees, dams or river dikes that alter the river flow (Faisal et al. 1999). The basic principle requires storage, diversion and confinement of floods. Non-structural measures involve numerous mitigation actions but do not include altering the river flow. They cover training, flood insurance, assessment methods, emergency services, land-use planning, construction codes, warning and forecasting, etc. (Ballesteros-Cánovas et al. 2013). The goal is to reduce loss of life and property, but it is inevitable, even structural measures could have useful consequences for a specific period; they also lead to potential threats as well because they rebuild natural processes but do not follow natural rules (Gao et al. 2007).
In flood risk management, flood risk is generally based on three factors: hazard, exposure and vulnerability (Roberts et al. 2009). Hazard is the extreme natural event including its frequency; exposure refers to the people, their environment and properties affected by flood; and vulnerability refers to the susceptibility of people and properties and the coping capacity to deal with flood impact (Kron 2009). In this regard, to decrease the impact of flood through flood management, the evaluation of flood risk constituents is unavoidable. Hence, evaluation of vulnerability is an important element of flood management and decreasing vulnerability is becoming more significant aspect of this kind of management, with population increasing in urban areas (Ahmad and Simonovic 2013). To achieve this aim, vulnerability assessment methods development is very appropriate (De Moel et al. 2012). There are diverse distinctions in the current methodologies for hazard vulnerability around the world. As regards to previous works with emphasizes on flood hazard, vulnerability assessment primary methods can be clustered into three groups (Huang et al. 2012).
Table 1 mentions these methods which are used by other researchers and describes the brief weaknesses and strengths of each group.
In the context of cities, urban planners have expanded urban management measures to tackling hazard impacts by simplifying the decision-making process and helping city authorities (Kang 2009).One of these measures is presenting new indexes for assessing vulnerability and recognizing more vulnerable regions.
Current paper presents attempts to decrease the scale of flood vulnerability index from large city to district scale of inner city, because different scales have dissimilar indicators which make them vulnerable to floods. This is desired for orienting future urban growth away from risk areas and promotes a resilient-district concept for which there is a need to recognize the most vulnerable areas of each city. The previous flood vulnerability indexes focus on large scale neglecting some of the factors which change the vulnerability of smaller spatial scales, such as urban districts. Accordingly, this study aims to develop flood vulnerability index with significant local factors and provides more comprehensive interpretation of these factors being suitable for district scale.
Urban systems can be vulnerable to floods because of three main aspects: exposure, susceptibility and resilience. As such, vulnerability of urban area reflects the exposure and susceptibility of the city to flooding and the resilience of that region to cope and recover from the impact of the flood. (Smit and Wandel 2006).
As mentioned, for assessing vulnerability of human systems, one of the simple methods is index construction. The index is a quantitative variable that would allow comparison of the disaster risk and its impacts between varied areas exposed to flood. (Birkmann 2007) Every index is conducted first by identifying the most suitable type of data to counting vulnerability and second recognizing available data at the spatial scale of study (Mclaughlin and Cooper 2010). The indexes let us to identify aims and provide strategies guidance to reduce vulnerability and to set more precise and quantitative targets for vulnerability decrease. (Balica 2007).
The flood vulnerability index is a method to assess flood vulnerability based on: river basin, sub-catchment, and urban area scales by categorizing different components that affect the susceptibility of the people who live in flood prone areas. The previous indexes identified four main social, economic, environmental and physical components which are specified by some indicators in (Balica 2007) research and Meteorological, Hydrogeological, Socioeconomic and Countermeasure Components in (Connor and Hiroki 2005) study.
Connor and Hiroki (2005) calculated this index for river basin system and stated that there are a lot of factors except precipitation and runoff, which influence a basin’s flood vulnerability such as preparedness and resilience capacity. They suggested four key components in a river basin, which affect flood vulnerability; Meteorological Component (MC), Hydrogeological Component (HC), Socioeconomic Component (SC), and Countermeasure Component (CC). Balica (2007) extended this definition to sub-catchment and urban systems. She recognized another four components for these two scales: economic, environmental, social and physical components, which can be assessed by various indicators. Interaction between these components and the mentioned factors of the system (exposure, resilience and susceptibility) is the basis of flood vulnerability index methodology (Fig. 1). The social component ensures the vulnerability of an area to a flood in terms of social development. Physical components include physical condition, both natural and artificial, which affects flood vulnerability of a specific area. Environmental component consists of indicators which mention the environmental damages caused by flood hazard or artificial interventions, which can raise the vulnerability of a particular area and finally economic components include economic issues such as income, economic activities, industries, agriculture and power production, which are affected by flooding (Balica 2007).
As regards to this theoretical framework, for introducing flood vulnerability index for Kuala Lumpur context, it is essential to identify the flood vulnerability components (physical, economic, environmental and social) and their indicators for Kuala Lumpur city and determine the most significant indicators which are appropriate for the district scale through expert opinions and regulate weights of selected indicators to define the index then at the end construct the district flood vulnerability index (DFVI) for Kuala Lumpur districts.
Malaysia case study
Malaysian cities are fortunate as they do not face hazards like earthquakes, but intensive floods happen regularly. Flash floods and monsoon floods are two kinds of floods that occur rather frequently in Malaysia. Table 2 displays the most serious flood events in Malaysia between 1950 and 2015 which are arranged by number of people affected and extent of economic losses. But few studies have been done on introducing indexes on this area.
In fact, DFVI approach is one of the initial index methods for flood vulnerability assessment in urban district scale and the first structured effort to assess flood vulnerability with indexes in Malaysia. This will be more imperative when vulnerability assessment is a requirement of the European flood directive 2007/60/EC (Parliament and Committee 2007) for reducing natural hazard risk. In such a way, Kyoto 2005 manifesto (governments across the world obligate to proceed for reduce disaster risk and approved a guideline to decrease vulnerabilities to natural hazards, called the Hyogo Framework for Action (HFA)) has mentioned indicators-based approaches to different scales for observing disaster risk and vulnerability, and rise the capability of countries to manage risks (United Nations 2005; Balica et al. 2013). As a result, the indicators through the index can be a director to understanding the current and future state of an area in facing with natural hazards.