One of the major determining flood-prone areas is the slope. The map classified the slope into five ranges, namely: Very Low, Low, Moderate, High, and Very High. Areas which have lower slopes have a higher probability of being flood-prone (Very Low and Low).

This rainfall map of the Alappuzha district depicts spatial variation in the intensity of rainfall across different taluks. Cherthala and Chengannur taluks are deep red in color, portraying regions with very high rainfall values (>8.109 mm). High rainfall (7.537– 8.108 mm) is also observed at some places in the Ambalappuzha and Kuttanad regions.

The geomorphic divisions of the study area include the alluvial plain, coastal plain, lower lateritic plateau, marshy lands, mud flat, flood plain, residual mount, swale, valley, and waterbody. Coastal plains and alluvial plains in the low-elevated regions (Cherthala, Ambalappuzha, and Kuttanad) are more prone to inundation as the topography is flat, favoring the flood.

Regions with very high and high drainage densities, such as Cherthala, Ambalappuzha, and Kuttanad, are highly prone to flooding because the dense drainage network gets saturated during heavy rainfall events thereby causing waterlogging and even submergence. Conversely, low and very low drainage density areas have less vulnerability due to the reduced capacity of the drainage network to hold surplus water.

Soil texture determines the rate of flooding. Impermeable soils with poorly drained, such as clay, enhance runoff rates, increasing the risk of flooding, especially in the lower elevated areas such as Ambalapuzha, Kuttanad, and northern parts of Chengannur.

The LULC of the district includes water bodies, wetlands, vegetation, built-up land, and agricultural land. The presence of wetlands and water bodies makes the northern and central parts highly vulnerable to floods. The majority of the built-up and agricultural lands can be found along these regions. Some of the vegetative areas is also seen in these low-lying areas whereas a major portion is predominant in the southern portion of the district which is at lower risk of flood.

NDVI value ranges from -1.0 to 1.0 and indicates the amount of vegetation within the land surface. NDVI values are between -0.285 and 0.705, which are categorized into five classes as -0.285 - 0.049 (very low), 0.05 - 0.212 (low), 0.213 - 0.348 (moderate), 0.349 - 0.457 (high), and 0.458 - 0.705 (very high). Dense vegetation indicated by high NDVI values can interrupt rainfall water and reduce the speed at which it reaches rivers or streams thus increasing infiltration into the soil.

The NDBI indices vary from -1 to 1 with a high value signifying built-up areas while the low value signifies other regions. The value of NDBI varies between -0.514 and 0.503 with five classes classification, that is, -0.514 - -0.223 (very low), -0.222 - -0.151 (low), -0.15 - -0.08 (moderate), - 0.079 - 0.016 (high), and 0.017 - 0.503 (very high). High NDBI-value built-up areas are dominated by impervious surfaces like roads and buildings, etc. cannot soak up rainwater; hence increased runoff and flooding are being experienced.

The WRI values range from 0.219 to 1.792 which are categorized into five classes as 0.219 - 0.491 (very low), 0.492 - 0.639 (low), 0.64 - 0.843 (moderate), 0.844 - 1.083 (high), and 1.084 - 1.793 (very high). WRI values greater than 1 usually represent the areas that contain waterbodies, which prove high in water-retention capacity.

MNDWI values of the study area are categorized into five classes such as -0.736 - -0.285 (very low), -0.284 - -0.205 (low), - 0.204 - -0.084 (moderate), -0.083 - 0.061 (high), and 0.062 - 0.542 (very high).

The socio-economic data of the study area were obtained from the Census of India. The parameters include total population, number of households, household size, literacy rate, building roof type, building condition, building wall type, child population, and access to information. The data obtained is then performed normalization which makes it easier for further processing.

The total population of the district ranges between the normalized values of -1.26 to 1.46 in which a value between -1.26 to -1.228 indicates a very low population that is experienced in the Kuttanad region due to its geographical factors. Moderate population (-1.227 - - 0.172) is found along the is observed along the elevated portion of Chengannur. High (-0.171 - 0.777) is observed along the southern portions (Karthikappally and Mavelikara) which is less prone to flooding. A very High population (0.778 - 1.46) belongs to the highly flood-vulnerable areas such as Cherthala and Ambalappuzha.

The child population ranges between the normalized values of -1.33 to 1.36 in which value between -1.33 to -1.119 indicates a very low population that is experienced in Chengannur. A moderate Population (-1.118 - -0.296) is found along the observed along Kuttanad and Mavelikkara. High (-0.295 - 0.432) is observed in Karthikappally which is less prone to flooding. Very High population (0.433 - 1.36) belongs to the highly flood-vulnerable areas such as Cherthala and Ambalappuzha.

Both maps show the highest number of households with larger household sizes (0.666 - 1.42) found in Cherthala taluk whereas Ambalappuzha, Karthikappally, and Mavelikara regions experience higher households with greater sizes (-0.023 - 0.665). Chengannur region observed moderate households (-1.194 - -0.024) as its an elevated portion of the district. Households and it is very low in the Kuttanad region (-1.37 to – 1.195).

The map depicts the building conditions of settlements in the district. A number of households with the condition of Census House are classified as good, livable, and dilapidated. Building condition is categorised into categorized into five classes such as < -0.96 (very low), -0.959 - -0.841 (low), -0.84 - -0.75 (moderate), - 0.749 - -0.192 (high), and -0.191 - 1.37 (very high). Only around 50-60% of settlements in the highly and very highly vulnerable regions are in good condition, 25-30% as livable, and the rest as dilapidated which is highly prone to flooding. These are evident in Cherthala, Ambalappuzha, and Kuttanad.

The map depicts the building conditions of settlements in the district. A number of households with the condition of Census House are classified as good, livable, and dilapidated. Building condition is categorised into categorized into five classes such as < -0.96 (very low), -0.959 - -0.841 (low), -0.84 - -0.75 (moderate), - 0.749 - -0.192 (high), and -0.191 - 1.37 (very high). Only around 50-60% of settlements in the highly and very highly vulnerable regions are in good condition, 25-30% as livable, and the rest as dilapidated which is highly prone to flooding. These are evident in Cherthala Ambalappuzha and Kuttanad.

Wall condition is categorized into five classes such as < -2.18 (very low), - 2.17 - 0.0186 (low), -2.17 - 0.0186 (moderate), 0.329 - 0.603 (high), and 0.604 - 0.74 (very high). According to census type, wall condition is divided into several types such as Grass/ Thatch/ Bamboo. Plastic/ Polythene, Mud/Unburnt brick, Wood Stone not packed with mortar, Stone packed with mortar, G.I./ Metal/ Asbestos sheets, Burnt brick, Concrete, and any other material. The majority of the houses in the study area have walls made of burnt bricks and concrete type.

Roof condition is categorized into three classes such as < -1.22 (low), -1.219 - 0.005 (moderate), and 0.006 - 1.22 (high). Roof condition is divided into several types such as Grass/ Thatch/ Bamboo. Plastic/ Polythene, Mud/Unburnt brick, Wood Stone not packed with mortar, Stone packed with mortar, G.I./ Metal/ Asbestos sheets, Burnt brick, Concrete, and any other material. Houses with tiles and concrete are less prone to flooding. Other roof types are less resistant to flooding.

Literacy plays an indirect role in mitigating the rate of the flood as it enables one to gain knowledge about the pre and post-flood events. Chengannur, Kuttanad, and Mavelikkara taluk have higher literacy rates with 88.87%, 88.21%, and 87.47% respectively. Cherthala has a moderate literacy rate with 86.95%. Ambalappuzha accounts for about 86.57% with low literacy. A very low literacy rate is found in Karthikappally with 86.08%.

Information assets per census type include radio/transistor, television, computer /laptop, and telephone/mobile phone. High flood-prone areas such as Ambalappuzha and Kuttanad have lower access to these assets, making them more vulnerable to population. Cherthala and Mavelikara have moderate access to information. Chengannur has accounted for the highest information assets.

The flood risk map of Alappuzha district in Kerala highlights major taluks such as Cherthala, Ambalapuzha, Kuttanad, Karthikappally, Chengannur, and Mavelikkara, showing varying levels of flood susceptibility. Low-lying coastal and riverine areas are especially prone to flooding, as indicated by the Weighted Overlay Method. The district is predominantly agricultural, with 80% of it in coastal areas and a long 82 km coastline. Taluks like Cherthala, Ambalapuzha, and Kuttanad, located in lowland regions, are categorized under very high to high flood-risk zones. These areas experience heavy precipitation and are close to major rivers, backwaters, and Vembanad Lake, exacerbating flood risks. The alluvial plains of Kuttanad, known as the "Rice Bowl of Kerala," are particularly vulnerable as they lie below sea level, with sloping topography contributing to flooding during the monsoon season.

The proximity to rivers like Pamba, Manimala, and Achankovil further increases flood susceptibility. This has a significant impact on local agriculture with farmers losing crops annually. Ambalapuzha, on the periphery of Kuttanad, faces moderate to high flood risks, affecting the agricultural livelihoods of farm households. Cherthala, a coastal plain near the lake is highly prone to flooding, especially during the monsoons when water from lakes and rivers swells the area.

While the southern regions of Karthikappally, Chengannur, and Mavelikkara are at higher altitudes, they still face moderate flooding due to nearby rivers. In highly vulnerable areas, 50-60% of settlements are in good condition, with the rest in poor or dilapidated states. Literacy rates are low and the area faces challenges in reducing disaster vulnerability.

The authors would like to thank Dr. T K Prasad, Associate Professor and Head of the Department of Geography at Kannur University, for his support throughout this Case Study.

We would like to thank Observation and Science (EROS) for their free access to the images Orbview-3 and Sentinel-2 via the website https://earthexplorer.usgs.gov/. The authors are also thankful to the reviewers for their useful remarks and recommendations.