Development of Flood-Hazard-Mapping Model Using Random Forest and Frequency Ratio in Sumedang Regency, West Java, Indonesia

Flooding, often triggered by heavy rainfall, is a common natural disaster in
Indonesia, and is the third most common type of disaster in Sumedang Regen
cy. Hence, flood-susceptibility mapping is essential for flood management. The
primary challenge in this lies in the complex, non-linear relationships between
indices and risk levels. To address this, the application of random forest (RF)
and frequency ratio (FR) methods has been explored. Ten flood-conditioning
factors were determined from the references: the distance from a river, eleva
tion, geology, geomorphology, lithology, land use/land cover, rainfall, slope,
soil type, and topographic wetness index (TWI). The 35 flood locations from
the flood-inventory map were selected, and the remaining 18 flood locations
were used for justifying the outcomes. The flooded areas from the RF model
were 28.39%; the rest (71.61%) were non-flooded areas. Also, the flooded ar
eas from the FR method were 8.02%, and the non-flooded areas were 91.98%.
The AUC for both methods was a similar value – 83.0%. This result is quite ac
curate and can be used by policymakers to prevent and manage future flooding
in the Sumedang area. These results can also be used as materials for updating
existing flood-susceptibility maps.