Present vs. Future Losses from a 100-year Flood: A Case Study of Grand
Isle, Louisiana
Abstract
Louisiana is among the most vulnerable places on Earth to coastal
flooding, for many reasons. Tropical-cyclone-induced storm surge,
shoreline erosion accelerated by eustatic sea level rise, tidal
influences, minimization of river sediment nourishment due to the
presence of levees, and land subsidence caused by compaction of marsh
lands and underground resource extraction all contribute to the flood
hazard. In addition, increasing frequency and intensity of natural
hazards under climate change scenarios are expected to exacerbate the
coastal flood risk. Many studies focus on flood risk assessment and
mitigation strategies both for the present and future, and other
research has analyzed future flood risk considering climate change and
sea level rise. Yet few studies consider all of these factors in
concert. This research represents a comprehensive approach that
considers coastal subsidence, eustatic sea level rise, and tropical
cyclone storm surge variability under climate change scenarios, to
evaluate future flood risk at the individual building level in Grand
Isle, Louisiana. Results suggest that on average, the 100-year flood
depth will increase by 37 cm at the individual building level in Grand
Isle by 2050, with subsidence contributing over 80 percent of this
increase. Subsidence is projected to increase structure and content
losses by approximately 18 percent above modeled losses at present,
while eustatic sea level rise may contribute approximately one percent
of additional losses. A 100-year storm surge event amid a “low”
scenario of environmental change would increase the structure and
content losses at Grand Isle by 68–74 percent of today’s value in ten
years, 141–149 percent in 25 years, and 346–359 percent in 50 years.
Even more menacingly, “high” scenarios of environmental change are
expected to increase the 100-year storm surge losses by approximately
85–91 percent of today’s value in ten years, 199–218 percent in 25
years, and 407–415 percent in 50 years. Outcomes from this study will
fill the gap in the current literature by implementing a more realistic
risk assessment model and will direct flood risk managers, property
owners, and other stakeholders to build a comprehensive framework to
minimize future flood risk in one of the most vulnerable sites in the
USA to coastal flooding.