Natural hazard mitigation in a rapidly changing world: Louisiana as a ‘canary in the coal mine’ for coastal flooding

Natural disasters related to weather and climate, including heat waves, droughts, wildfires, and flooding, are increasingly costly. A variety of natural and human-caused factors are involved. For mitigation purposes, it is important to consider which factors are important, how they will change, and how fast. Coastal Louisiana is a good example. Like many coastal areas around the world, the state is suffering from the increased cost of coastal flooding. Unlike many of these areas, Louisiana has also experienced significant long-term land loss from the combined effects of coastal subsidence and eustatic sea level rise. The state is wrestling now with issues that other coastal communities will face in coming decades. Current planning and flood mitigation policies in Louisiana and many coastal communities assume the present-day coastline is a relatively static feature. This view reflects a temporally biased focus on short-term or past causes of land loss and an assumed low rate of sea level rise. Accelerating sea level rise, a consequence of accelerating concentrations of atmospheric CO2 and corresponding increases in ocean and atmospheric temperature, will soon be the major cause of land loss and flooding in Louisiana and other coastal areas around the world. It is not easily mitigated and requires new, forward-looking approaches. While levee and seawall enhancement, sediment diversion, and raising of vulnerable structures are useful short-term approaches, some retreat from current coastlines will also be required.