GIS-Based Flood Risk Assessment in the Johor River Basin Using AHP and Weighted Overlay

Abstract

Flood-risk studies in Malaysia have often concentrated on hydrological hazard, although the consequences of flooding also depend on where people and assets are located and how well communities can cope. This study develops a basin-wide flood-risk index for the Johor River Basin by integrating hazard, exposure and vulnerability within a geographic information system-based multi-criteria decision analysis. Nine hazard indicators, four exposure indicators and four vulnerability indicators were assembled from open geospatial datasets. The indicators were standardised into five ordinal classes, weighted using the Analytic Hierarchy Process, and combined through weighted overlay. The three component indices were then assigned equal weights to produce a composite flood-risk surface. High and very high risk covered 9.29% and 1.43% of the basin, respectively. These areas were concentrated around Kota Tinggi in the lower basin and, in smaller clusters, around Bandar Tenggara in the middle basin. A spatial consistency check used 24 locations listed in a Department of Irrigation and Drainage flood warning for 14-17 December 2025. Nineteen locations (79.17%) fell within high or very high risk classes, while 23 (95.83%) fell within moderate to very high classes. The resulting map is best interpreted as a relative screening tool for prioritising detailed investigation, land-use control and preparedness. Its main limitations are the use of mixed-date datasets, subjective weighting, a climatological rainfall surface, and the absence of hydrodynamic simulation and observed inundation footprints.