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Study: Coastal communities to face 100-year floods annually

Coastal communities could face 100-year flooding annually until the end of the century.

Posted on September 18, 2023

Due to climate change, glaciers are melting rapidly due to the warming global temperature, which is causing the sea levels to rise further, leading to the severity and frequency of coastal flooding.

Irrespective of the moderate carbon emission scenario, 100-year floods will occur globally in coastal regions. These types of floods can hit the same areas numerous years in a row or possibly not strike at all within the century.

Unpredictable events

Formerly, scientists predicted, based on historical empirical data, that a 100-year flood – high water level has a one percent probability of happening in any given year.

However, a new study finds that these historical trends will no longer help predict the possibilities of future floods accurately.

Hamed Moftakhari, a civil engineer and professor at the University of Alabama and supervisor of the study, stated:

“The threshold that we expect to be exceeded once every hundred years on average is going to be exceeded much more frequently in a warmer climate until they are no longer considered 100-year events.”

Usually, floods can be triggered by water being pushed inwards toward the land from the sea due to storms or tides and waves in coastal areas. The recent study aimed to identify a long-term triggering element leading to flooding over a long period and the role of rising sea levels.

As the ocean’s water level rises, the water is bound to reach ashore. As a result, the coastal infrastructure, which is positioned closer to the water, could face the direct force of storms and rising tides and waves. This would severely impact the communities in the regions, particularly their livelihoods.

Non-uniform extreme sea levels

To conduct empirical research, the researchers employed non-stationary methods and found that extreme sea-level shifts will not be uniform for many tide-gauge locations, Science Daily reported.

Information gathered from 300 tide gauges worldwide was analyzed to establish the global flooding pattern. Researchers made further projections regarding future extreme sea levels using two carbon emission scenarios highlighted by the International Panel on Climate Change.

The scenarios involve a situation when carbon dioxide emissions continue to rise until the end of the century. Secondly, when emissions peak by 2040 and then decline upon climate action.

Considering both scenarios, the study concluded that rising sea levels will result in a more significant occurrence of 100-year flood events in most of the areas they examined.

Moftakhari told Science Daily that a proactive approach to land planning, urban development, and coastal protective measures could help communities reduce flooding and avoid disaster, and that starts with realistic forecasts of future coastal conditions.

Tackling floods

Additionally, Moftakhari alludes to some standard practices that civil engineers deploy – a stationarity concept to project future water levels while designing structures such as sea dykes, seawalls, and breakwaters to protect communities from extreme floods.

“In stationarity, we assume that the patterns we have observed in the past are going to remain unchanged in the future, but there are a lot of factors under climate change that are modulating these patterns,” added Moftakhari. “We can’t assume stationarity in coastal flooding anymore.”

The civil engineer also noted challenges in calculating future flood risks, stating that most tools, design guidelines, manuals of practice, and more are all based on the assumption of stationarity. The current structures need to be updated to keep pace with the rate of change.

The study emphasized that more than 600 million people could be affected as they are situated in mostly low-lying coastal areas. The residents could be protected by well-designed structures in these regions that can resist significant flooding.

The impact is already observable in regions like the Gulf of Mexico, where the sea level rises faster than the global average due to land sinking. Such localities will require custom solutions to meet their protection needs.

Moftakhari stated: “We know that mean sea level is rising; the question is: how are we going to deal with it? We’ve already seen that many portions of the coast are permanently inundated and losing land. Many coastal cities and islands are experiencing flooding much more frequently than in the past — it’s time to learn how to deal with non-stationarity.”

“Don’t forget that this is all about the level of water that we expect to experience without mitigation measures,” he noted. “There will be technological advancements that could enhance the resilience of communities.”

The study was published in Earth’s Future on July 5.


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