Detecting Flood Susceptible Areas Using GIS-based Analytic Hierarchy Process

Speedy growth of the world’s population has escalated both the frequency and severity of
the natural catastrophes nowadays. Flood disaster has a very special place in natural catastrophes and its
effect area is not bounded. It is the unusual event of river basins due to a prolonged rainfall and related
humankind activities. Floods are the costliest types of natural catastrophes in the world and it accounts for
31% of the economic losses resulting from natural catastrophes. This paper is part of the ongoing project
aimed at identifying the areas that are likely to be inundated by significant flooding based on the reviewed
flood contributing factors of the study area. Multi-Criteria-based Evaluation (MCE) method is adopted in
detecting the flood susceptible areas around the river basin of the study area of Perlis, Malaysia. The MCE
method used is the pair-wise comparison methods of Analytical Hierarchy Process (AHP). Questionnaires
were distributed to experts on hydrology and hydraulics in order to score each flood contributing factor used
as criterion separately in their order of significance. Pair-wise comparison method was used in calculating the
weights of each criterion. Some of these flood causative factors considered herein are the annual rainfall,
capacity of the existing drainage, size of the watershed, land use, soil type and the slope. The weights derived
shows C1= annual rainfall and C2= capacity of the existing drainage to be the most flood contributing factors
based on the decision makers’ preferences. However, the results of this analysis will further be overlaid for
the flood susceptibility mapping for the presumptive flood areas around the river basin of Perlis into the GIS
environment. This will be carried out in the subsequent study as this paper is part of the ongoing project. The
flood vulnerable areas to be delineated will correspond to those areas that are likely to be inundated by significant flooding. Additionally, further risk analysis will be performed using Digital Elevation Model (DEM) data, distance from hazard zone, land cover map and potential damageable objects at risk. DEM will be used to delineate the catchments and serves as a mask to extract the highest hazard zones of the flood vulnerable area(s). The final results will be incorporated to Web-based GIS using Mash-up to serve as an interface.