Land subsidence in Houston correlated with flooding from Hurricane Harvey

Hurricane Harvey caused unprecedented flooding and socioeconomic devastation in Eastern Texas with high winds, elevated storm tide, and record rainfall. The flooded area is mapped using the radar backscattering difference between Sentinel-1A/B satellite acquisitions spanning the event, which provides a snapshot of standing water at the time of image acquisition. We find vast areas outside of designated flood hazard zones are overwhelmed. Furthermore, we map pre-cyclone land subsidence using multitemporal interferometric processing of large SAR datasets acquired by Advanced Land Observation Satellite (ALOS) and Sentinel-1A/B satellites. We find that subsidence of up to 49 mm/yr and 34 mm/yr during the ALOS (Jul-2007-Jan-2011) and Sentinel-1A/B (Dec-2015 to Aug-2017) acquisition periods affect various parts of Houston-Galveston area. We conclude that 85% of the flooded area subsided at a rate > 5 mm/yr. We suggest that subsidence affected flood severity by modifying base flood elevations and topographic gradients, supported by the Chi-square test of independence. This work highlights the importance of incorporating InSAR measurements of land subsidence in flood resilience strategies.