Analysing Flood Vulnerable Areas with Multicriteria Evaluation

Cell-based Multicriteria Evaluation (MCE) methods are used to analyse the flood vulnerable areas. Flood disaster has a very special place in natural hazards. Its effect area is not bounded; it is an unusual event of a river basin. The aim in integrating Multicriteria Decision Analysis (MCDA) with Geographical Information Systems (GIS) is to provide more flexible and more accurate decisions to the decision makers in order to evaluate the effective factors. Some of the causative factors for flooding in watershed are taken into account as annual rainfall, size of watershed, basin slope, gradient of main drainage channel, drainage density, land use and the type of soil. In this study two main MCE approaches employed in GIS are used, namely Boolean and Weighted Linear Combination (WLC), and the issues and problems associated with both are discussed. In MCE, two methods, namely Ranking Method and Pairwise Comparison Method, are used to calculate the weights of each factor. Pairwise Comparison Method is integrated in GIS. An interface for pairwise comparison is created in Visual Basic Application embedded in ArcView 8.1 which is a GIS software program. The different results obtained from these two methods indicate the importance of the decision maker in determining the weights and the proper method, and making the decision. Furthermore, the concept of uncertainty in standardized criteria with MCE is evaluated. The standardized values of the factors are considered as a fuzzy measure concept expressed as fuzzy set membership. Some regular weights that are determined using Ordered Weighted Averaging are combined with the standardized values using WLC to recast the vulnerable areas. Thus the distribution of the weights of the criteria and compensating for each criterion by another one are seen in the solution set. A case study of flood vulnerable areas determination in Bartın Basin in the West of Black Sea Region is employed to illustrate the different approaches. To store the existing flood vulnerable areas in decision support system of General Directorate of Land Registry and Cadastre will provide some advantages to able to get answer for the questions of “How much area is vulnerable to flood?, What amount of the total area belongs to the government, or the real or judicial person?, Is there any area to be able to exchange by the treasury goods? How much?, what are the needs and cost to move through the non-vulnerable areas?”.