Global coastal communities face increasing risk of annual floods, even under a moderate emissions pathway that peaks by 2040. A landmark study projects that by the end of the century, many regions will experience major floods far more often than once per century. In some scenarios, regions could see such events every nine to fifteen years as soon as 2050.
The term flood of the century describes an extreme water level with a 1% annual exceedance probability, based on historical patterns. But new research suggests that relying on historical averages will no longer capture future risk. These megafloods, while severe, can recur in consecutive years or not occur at all within a single century, depending on shifting climate dynamics.
Coastal flooding results from water pushed inland by storms, tides, and waves. The study, however, concentrates on a longer-term contributor: rising sea levels. As seas rise, coastal infrastructure sits closer to the water, magnifying the impact of storms, tides, and waves on population centers.
Waves striking the shoreline near city centers have become a visual reminder of these risks. Researchers analyzed data from more than 300 tide gauges worldwide to track trends and forecast future extreme sea levels under two emissions scenarios. One scenario assumes continued growth in carbon dioxide emissions through the century, while the other envisions peaks around 2040 followed by a decline. In both cases, the analysis shows rising sea levels will drive more frequent and severe floods in many study locations.
Hamed Moftakhari notes that better spatial planning, urban development, and coastal protection measures can reduce flood impacts and help communities avert disasters.
Building a safer future
Engineers who design defenses such as seawalls and breakwaters use a concept called stationarity to project future water levels. In stationarity, past patterns are assumed to persist into the future. Yet climate change is altering those patterns, making it clear that coastal floods may not behave as they did before.
Earlier studies relied on fixed estimates of extreme sea levels to predict 100-year floods. The latest work uses nonstationary methods and finds that changes in extreme sea levels will not be uniform across locations.
As the climate continues to warm, ocean temperatures rise and glaciers melt, driving higher sea levels and more frequent coastal flooding. This reality underscores the need for accurate risk estimates that acknowledge shifting baselines rather than assuming past patterns will hold.
The situation is no longer stable
The uncertainty arises because many tools, design guidelines, and application guides have been built on stationary assumptions. Those expectations must now be revised to reflect the pace of change, according to Moftakhari. A recent study estimates that more than 600 million people live in low-lying coastal zones, with that number climbing as risk grows. Well-designed coastal defenses play a crucial role in strengthening community resilience to major floods.
Coastal impact will not be uniform worldwide. In higher latitudes, some regions may see relative drops in sea level as ice sheets melt and land rebonds, while areas like the Gulf of Mexico may experience faster rises due to land subsidence. Moftakhari emphasizes that each region requires tailored solutions based on local conditions.
As he puts it, the question is not whether sea levels will continue to rise, but how communities will respond. With permanent land loss and frequent flooding affecting many coastal areas, it is essential to learn how to manage nonstationary flood risks now.
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Note: Safeguards and planning strategies discussed here emphasize the need for adaptive design, flexible engineering, and proactive community action to withstand evolving flood hazards.