An integrated statistical-geospatial approach for the delineation of flood-vulnerable sub-basins and identification of suitable areas for flood shelters in a tropical river basin, Kerala

Flood vulnerability assessment is crucial for developing effective flood management and mitigation strategies. The present study aims to understand the flood vulnerability of the Kallada River Basin (KRB) and identify suitable locations for safe flood sheltering facilities in the basin. As part of this, morphometric analysis of KRB was carried out by dividing the basin into fifty-eight 4^th-order sub-basins to understand the sub-basin-wise terrain characteristics and the degree of vulnerability to flooding. GIS tools were used to assess various morphometrical parameters, such as drainage frequency, texture ratio, ruggedness number, basin relief, bifurcation ratio, length of overland flow, drainage density, circularity ratio and area, and geo-environmental factors such as sand percent, rainfall, and mean slope of these basins. The morphometric parameters exhibited distinct spatial trends, with higher values primarily concentrated in the east and northeast parts for certain parameters and in the western parts for others. Using hierarchical cluster analysis, the sub-basins were categorized into six clusters, revealing that 51% were vulnerable to floods, 26% moderately vulnerable, and 22% not vulnerable. Sub-basins in the central and western KRB were found to be highly vulnerable to flooding, while those in the eastern parts showed moderate vulnerability or were not vulnerable. Flood vulnerability mapping was validated using flood data of 2018 and 2019. Additionally, the weighted overlay method identified suitable areas for flood shelters in moderately vulnerable and vulnerable sub-basins and the areas were categorized into highly suitable, suitable, moderately suitable, and not suitable areas. Most areas of SB53 and SB55 were found highly suitable, emphasizing their potential for flood shelter locations. The findings of this study can be used by competent authorities to initiate flood mitigation and to develop targeted flood preparedness measures in similar river basins, particularly in the context of increasing flood events.