A Map That Does Not Predict: Flood Hazard Area and Realised Events Across Indonesian Provinces
Keywords:
flood hazard mapping, disaster risk assessment, hazard and risk, exposure, indicator validationAbstract
A national hazard map is used to allocate protection, so whether it corresponds to where events occur is worth testing. This article compares the flood hazard areas published in Indonesia's national risk information system against the flood events recorded by province in 2025. Across the 34 provinces for which hazard data is returned, the correlation between hazard area in hectares and the number of recorded flood events is minus 0.079, and rises only to 0.106 when two mislabelled entries are removed. The number of people the same system records as exposed correlates with events at 0.802, but that quantity is close to a measure of population and does not validate the map. The ratio of events to hazard area spans four orders of magnitude, from 701 events per million hectares in the Special Capital Region of Jakarta to 0.097 in one Papua-region entry. The article argues that the divergence is expected rather than anomalous, because a hazard map records where inundation is physically possible while an event record counts where inundation reached people and was reported, and that the two are used interchangeably in ways the data does not support. It also documents that the hazard system carries no version date, returns nothing for four provinces, and labels two entries inconsistently with their underlying values.References
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