An Information System for Risk-Vulnerability Assessment to Flood

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1. Introduction

Records of loss of life and damage caused by floods worldwide show that these have continued to rise steadily during recent years. Understandably, the response has been to call for increased efforts to protect life and property. The sustainable and effective management of floods demands a holistic approach--linking socio-economic development with the protection of natural ecosystems and appropriate management links between land and water uses. It is recognized that a watershed is a dynamic system in which there are many interactions between human population, land use and water bodies. Assessment and mapping of "flood risk" [1-7] and "vulnerability to flood", and dissemination of the appropriate information to different stakeholders is a very important part of the flood management process. The general public may use the information in purchasing a house, or in selecting a site to start a business. Knowledge of flood risk could aid decision-makers in: developing land development plans and land use zoning; planning emergency response strategies; waste disposal site selections; preparing infrastructure budgetary decisions; developing guidelines for operation of existing infrastructure; and general policy development at all levels. Water management professionals can utilize the flood risk information in planning, design, construction, and operation & maintenance of flood protection infrastructure (e.g., reservoirs, dikes, drainage pipes, etc). Flood risk mapping has been performed extensively for effective flood management, starting with the pioneering work of Garrett [8]. The risk of flooding to towns and villages along 200 km of the River Thames and its tributaries are assessed using a mathematical model developed for Thames Water Rivers Division, UK. The River Thames Strategic Flood Defence Initiative examines the vulnerability of floodplain development along the river. The achievements of the Flood Risk Mapping Program, New Brunswick, Canada, are summarized by Burrell and Keefe [9]. The procedures used to produce flood risk maps are outlined very clearly along with an assessment of the accuracy achieved. Floyd [1] performs a flood risk assessment on the city of Bombay (Mumbai), India. The results provide an initial indication of the cost-effectiveness of different remedial measures. Morris and Flavin [10] present maps of England and Wales showing the built-up areas that would be at flood risk. Shrubsole [11] mentions government responsibilities in flood management of the Saguenay and Red River valley and provides alternative flood management strategies considering ecosystem management, partnerships and the role of science. Hall et al. [12] represents the processes of fluvial and coastal flooding over linear flood defence systems in sufficient detail to test alternative policy options for investment in flood management. Potential economic and social impacts of flooding are assessed using national databases of floodplain properties and demography. A case study of the river Parrett catchment and adjoining sea defences in Bridgwater Bay in England demonstrates the application of the method and presentation of results using Geographic Information System (GIS). Barredo et al. [13] aims to illustrate a framework for flood risk mapping at pan-European scale produced by the Weather-Driven Natural Hazards (WDNH). The threatening natural event is represented as the hazard component, and furthermore, exposure and vulnerability are considered as anthropogenic factors that contribute also to flood risk. The flood risk is considered on the light of exposure, vulnerability and hazard, and mathematically considered as product of hazard, exposure and vulnerability.

Vulnerability assessments have been undertaken to understand the "potential for loss", traditionally they focused on the nature of the hazard and who and what are exposed [14]. More recently, vulnerability assessments have explored the social, economic, and political conditions that are likely to affect the capacity of individuals or communities to cope with or adapt to hazards [15]. Bender [16] discusses the development and use of natural hazard vulnerability assessment techniques in the Americas. He emphasizes how and why a thorough vulnerability analysis is required for physical, economic and social planning in a watershed. There are numerous studies that have addressed contemporary vulnerability of different communities worldwide to flooding from the natural hazards perspective of understanding exposure and the number of people and structures affected [17,18] but few that explore the socio-economic aspects of flooding vulnerability [19-22]. Recently, the conceptualization on social vulnerability has gained prominence in the literature. It is related to characteristics that influence an individual's or group's ability or inability to anticipate, cope with, resist, and recover from or adapt to any external stress such as the impact of flooding [23-25]. Cutter et al. [26] present a method for assessing vulnerability in spatial terms using both biophysical and social indicators. Their results suggest that the most biophysically vulnerable places do not always spatially interact with the most vulnerable populations. Flax et al. [27] develop a risk-vulnerability assessment methodology named as Community Vulnerability Assessment Tool (CVAT), which assists emergency managers in their efforts to reduce vulnerabilities through hazard mitigation, comprehensive land use and development planning. Cutter et al. [28] list factors that have gained consensus among social scientists as contributing to social vulnerability to environmental hazards. Blong [29] introduces a new damage index for estimating the replacement cost of damaged buildings in vulnerability analysis. Carter [30] analyzes flood risk as a combination of threat, consequence, and vulnerability. He discusses the federal role in investment decisions for flood control infrastructure. Chakraborty et al. [31] develop two new quantitative indicators, i.e., a geophysical risk index, based on National Hurricane Center and National Flood Insurance Program data, and a social vulnerability index, based on census information. Rygel et al. [32] focus on constructing a social vulnerability index and its application to a case study of hurricane storm hazard. They demonstrate a method of aggregating vulnerability indices for different indicators using Pareto ranking that results in a composite index of vulnerability, which avoids the problems associated with assigning weights. Werritty et al. [33] discuss the social impacts of flood events in Scotland including attitude and behavior toward flooding events, warnings, evacuations and consequences. The study suggests ways for enhancing social resilience for sustainable flood management in Scotland.

GIS is considered as a key tool by many researchers [34-38] to map the spatial distribution of flood risk and vulnerability to flood. A GIS facilitates the input, storage, management, analysis, integration, and output of spatial data which can aid with real time decision making and strategic planning for effective risk management and hazard preparedness [39]. GIS can improve warning, evacuation, and emergency response systems by helping route emergency response vehicles and locating emergency response facilities [39-40]. Exposures of soil and geology to flood, urban infrastructure, and socioeconomic data, can be input and stored in a GIS and then analyzed to identify areas prone to flood, identify vulnerable populations, and forecast flood events, and aid in land use zoning decisions to improve flood mitigation and management [17,39].

The flood risk mapping and analysis on various flood prone watersheds have been performed by many researchers throughout the world. In a recent study on Romanian national strategy, Varga et al. [41] provide basic information for preliminary flood risk assessments and flood hazard mapping in all areas with a significant flood risk, according to the Flood Directive. The technical and scientific approach and the main steps in setting up the plan for flood prevention, protection and mitigation at the river basin level are presented. Apel et al. [7] perform flood risk analyses in Eilenburg, Germany, especially in urban areas and tested a number of combinations of models of different complexity both on the hazard (probability of occurrence) and on the vulnerability. Chang et al. [42] examine the anthropogenic and natural causes of flood risks in six representative cities in the Gangwon Province of Korea. Tran et al. [43] explore the impacts of floods on the economy, environment and society; and tries to clarify the rural community's coping mechanism to flood disasters in Central Viet Nam. They reveal that flooding is an essential element for a coastal population, whose livelihood depends on productive functions of cyclical floods. Forster et al. [44] assess flood risk for a rural detention area, alongside the Elbe River in Germany. They find that the losses in agricultural areas exhibit a strong seasonal pattern, and the flooding probability also has a seasonal variation. The flood risk is assessed for a planned detention area based on loss and probability estimation approaches of different time frames, namely a monthly and an annual approach.

The present research study is motivated by the Hotspots project [45,46] completed by the Center for Hazards and Risk Research (CHRR) at Columbia University and the World Bank's Disaster Management Facility [DMF), now the Hazard Management Unit (HMU). In the Hotspots project, the risk levels are estimated by combining hazard or probability of occurrence with historical vulnerability for two indicators of risk--population and Gross Domestic Product (GDP) per unit area--for six major natural hazards: earthquakes, volcanoes, landslides, floods, droughts, and cyclones. The relative risks for each grid cell, rather than country as a whole, is calculated at sub-national scales. Such information can inform a range of disaster prevention and preparedness measures, and development of long-term land-use plans and multihazard risk management strategies. Hotspots global analysis and case studies stimulate additional research, particularly at national and local levels. The present study develops an information system for risk-vulnerability analyses to flood and facilitates vulnerability mitigation by providing various flood information to different users. The information system is designed to provide selective access to information on the bases of user needs. This reduces the misuse of data and promotes data security. A set of suitable vulnerability indicators and the procedure for their integration into an overall vulnerability index with high spatial density represent the major analysis tool within the information system. The additional innovations of the information system include: 1) the computation of selected flood risk-vulnerability indicators organized into themes from four components of vulnerability to flood, i.e., physical, economic, infrastructure, and social vulnerability [15], 2) the spatial infrastructure vulnerability analysis to flood due to inundation of main communication routes and road bridges, 3) the spatial flood impacts due to inundation of critical facilities (schools, hospitals, and fire stations) and 4) quantification of exposures of land use/land cover and soil permeability to flood. The postal codes or Forward Sortation Areas (FSA) are considered for spatial discretization of the region and flood risk evaluation. An interactive analysis tool is also developed for calculation of flood risk as a function of change in land use. The proposed information system is implemented …