Earth Observation Data-Driven Assessment of Local to Regional, Contemporary, and Emerging Coastal Environmental Security Challenges

Coastal zones are hotspots of global environmental changes. Worldwide, coastal environments face multiple, interactive stressors caused by both natural and anthropogenic impacts on climatic, oceanographic, ecological, and socio-economic processes such as sea level rise, storm surges, hurricanes, land subsidence, and population growth. The coastal U.S. is highly vulnerable to many of these climate and human-induced stressors. Over the past three decades, sea levels have risen by about 0.1 m along the U.S. coasts, with an additional projected increase of 0.2 to 0.3 m by 2050, and up to 2.0 m by the end of the century. The rise in sea levels will cause tides and storm surges to reach further inland, significantly altering flood regimes in coastal cities. By 2050, potentially damaging coastal flooding is expected to occur ten times as often compared to a baseline for the start of the 21st century. Moreover, these changes along the U.S. coastlines vary regionally and locally due to either positive or negative changes in land elevation over time (i.e., vertical land motion (VLM)). Lowering of land elevation (i.e., land subsidence) exacerbates sea level rise and the risk of inundation along coastal zones, presenting significant security challenges to coastal ecosystems, infrastructure, and populations. These dynamic and interacting stressors necessitate continuous monitoring to inform effective mitigation and adaptation strategies. Earth observation data allows for accurate, high-resolution, and continuous measurements of changing coastline. Despite the increasing availability of Earth observation data, current methods for monitoring VLM along coastlines lack the necessary spatial resolution and continuous coverage to accurately assess localized surface elevation changes. In this dissertation, I introduce a framework to jointly invert interferometric synthetic aperture radar (InSAR) and global navigation satellite systems (GNSS) data to provide semi-continuous measurement (50 m spatial resolution) of VLM for the contiguous U.S. coasts from 2007 – 2020. Combining the VLM dataset with projected sea level rise using different scenarios, I estimate flood hazards exposure for 32 major U.S. coastal cities by 2050, demonstrating that current measurements and frameworks underestimate flood vulnerability in several cities by not accounting for local and regional high-resolution VLM data. Next, I evaluate the possible drivers of land subsidence, exploring the relationship between spatio-temporal dynamic VLM and groundwater withdrawal from aquifers in major U.S. cities. Additionally, I assess the hazards and risks of land subsidence to infrastructure and wetlands along U.S. coasts. Finally, I extend this analysis beyond the U.S. coastline, investigating how land subsidence is linked to the incessant occurrence of building collapses in Lagos, Africa's most populous coastal city.