Table 4 Rationality of selecting flood risk factors

Elevation

Elevation and flood occurrence have an inverse correlation. It plays an important role in directing flood waters flow with low-lying regions that tend to experience a higher flood risk as gravitational force drives floodwater to flow from high to low elevated regions ^{55,56,62,73,74}

Building density

Higher building density can amplify both the likelihood and severity of urban flooding. As higher building density reduced the amount of permeable surface and natural drainage system that hinder surface runoff

Slope

The flood water accumulation process, infiltration process, and sedimentation process depend on the topographic slope as it has a direct effect on the speed and direction of flood water^75,76

Distance to roads

Concrete roads are also impermeable that prevents water percolation process and increased surface runoff

Aspect

The amount of rainfall and surface runoff depends on the topographic aspect because it refers to the specific direction of a topographic slope or land surface⁷⁷

NDBI

NDBI is positively correlated to flooding, as excessive amount inefficiently planned urbanization makes people and property more susceptible to flooding^77,78

Curvature

The curvature of a land surface influences the water budget of floodplains. It also helps to differentiate the regions where surface runoff diverges and converges ⁷⁹

Precipitation

Precipitation led rivers to overflow and inundate surrounding regions. Higher precipitation is often responsible for infrastructural damage and life loss^41,75,80

Median income

Demographic and socioeconomic factors are highly responsible for total flood risk^81,82,83. For example, income is highly correlated with individuals housing and surrounding conditions which indirectly increase the high risk of flood damage. Higher income peoples have more resources to prevent flood damage

NDVI

NDVI is negatively correlated with flood risk because dense vegetation cover obstructs surface water flow and promotes infiltration and percolation processes. While sparse vegetation and bare land facilitate rapid and unrestricted surface water flow into human settlements⁶²

Percentage of Hispanic population

Through their socioeconomic status, language barriers, limited access to resources, and occupational exposure Hispanic population potentially increasing their flood risks

Distance from waterbodies

Flood risk of a human settlement is strongly negatively linked with its proximity to waterbodies as the regions close to river and waterbodies tend to experience more inundation by flood water^74,77

Percentage of Black (African American) population

Through their socioeconomic status, language barriers, limited access to resources, and occupational exposure Black population potentially increasing their flood risks

TWI

TWI is a conceptual hydrological model that provides an indication of topographic wetness characteristics. It helps to understand surface flow as wetter regions tend to have rapid water flow compared to dryer regions⁸⁰

Percentage of people with no school completion

People with no schooling experience have very low awareness, fewer chances of employment, lower income, and less access to resources, all of which lead to a higher risk of flooding

Drainage density

Drainage density, a ratio between total channel length and basin area, influences surface runoff direction and water discharge. Higher drainage density refers to the high probability of flood risk⁷⁸