A Study on Flood Susceptibility Zones in Ernakulam District, Kerala, India Using the Frequency Ratio Model

Abstract

Flooding is one of the most frequent and destructive natural hazards affecting the low-lying coastal regions of Kerala, particularly Ernakulam District, which experiences recurrent flood events during the southwest monsoon. The present study aims to delineate flood susceptibility zones in Ernakulam District, Kerala, India, using the Frequency Ratio (FR) model integrated with Geographic Information System (GIS) techniques. A flood inventory was prepared using historical flood records and satellite-based data, while six flood-conditioning factors—geology, land use/land cover (LU/LC), soil, drainage density, rainfall, and slope—were selected based on their relevance to flood occurrence. Each factor was classified and weighted using the Frequency Ratio approach to evaluate its relative contribution to flooding. The results indicate that built-up areas exhibit the highest flood susceptibility (FR = 4.65), highlighting the impact of rapid urbanisation and increased impervious surfaces. In contrast, forest areas show minimal flood influence (FR = 0.17), emphasizing their role in runoff regulation. The factor ranking reveals that geology (FR = 7.73) is the most influential parameter, followed by LU/LC (FR = 6.90) and soil (FR = 6.58), while slope (FR = 1.60) has comparatively lower control over flood occurrence. Based on the weighted overlay of all factors, the study area was classified into different flood susceptibility zones ranging from low to very high. The findings demonstrate that the Frequency Ratio model is an effective and reliable tool for flood susceptibility assessment in data-scarce regions. The generated flood susceptibility map can support disaster risk reduction, urban planning, and sustainable flood management strategies, contributing to improved resilience against future flood events in Ernakulam District.