The longitudinal assessment of flood hazard in cities: Unlocking the floodplain record of Houston, TX, USA

Study Region: Houston, TX, USA Study Focus: The data-driven quantification of evolving urban flood hazard is challenging. Historical flooding data is readily available from the US National Flood Insurance Program, which has mapped Flood Hazard Areas (FHAs) since the 1970s. However, estimated FHAs are generally not used in modern flood studies due to the lack of georeferencing information. This poses a key impediment for fine-scale floodplain analysis, with critical implications for the study of urban flood change. This research develops a framework to automatically georeference historical Flood Insurance Rate Maps, and extract their floodplain data using photogrammetry, geomatics, and artificial intelligence. The registration framework is systematically validated to ensure the accurate extraction of longitudinal flood data. A median georeferencing residual of 23.1 m was obtained, which was smaller than the validation dataset accuracy. The framework provides an avenue towards the widespread assessment of longitudinal flood hazard, with significant implications for the study of urban flood resilience. Three flood-prone case studies are presented to exemplify the usefulness of the framework; Brays Bayou, Hunting Bayou, and Cypress Creek in Greater Houston. New hydrological insights for the region: The case studies quantify the change of flood hazard within these watersheds. Floodplain expansion had significant flood resilience consequences. Population exposure was estimated to have risen by up to 635%, with a concurrent increase in the vulnerability of critical infrastructure. • Develops framework to extract flood hazard data from historical flood insurance maps. • Framework is systematically validated, with good data extraction for GIS analysis. • Applies framework to three case studies in Greater Houston, TX, USA. • Flood hazard in case studies significantly expanded over time. • Critical flood resilience consequences for expanding hazard were discovered.