Sea level rise: Up to 13 million US homes at risk of flooding by 2100

Millions of US residents are at risk of flooding from sea level rise, say researchers from the University of Georgia. They say that if the sea level rises six feet by the turn of the century, 13 million American homes will be inundated.

Research published in Nature Climate Change analysed the total risk of sea level rise, in line with population projections. The researchers calculated the number of people at risk of flooding in all 319 coastal counties in the continental US.

The researchers used data for population projections to model the number of people living in coastal counties in 2100. They also used projections for global sea level rise for the same year; a rise of between three and six feet. They combined these two data sets to calculate the number of US homes at risk of flooding.

Up to 13.1 million at risk

They found that if the sea level rises by three feet – the lowest estimation – 4.2 million people will be at risk. Should the water level rise to six feet, that number will become 13.1 million.

"The impact projections are up to three times larger than current estimates, which significantly underestimate the effect of sea level rise in the United States," said Mathew Hauer, scientist working on the study. "In fact, there are 31 counties where more than 100,000 residents could be affected by six feet of sea level rise."

The model also showed that 25% of people living in the fastest growing communities will be susceptible to flooding with a six foot rise in sea level – including New Orleans and Miami.

Likewise, 80% of people living in the three most exposed counties are at risk. These counties include Monroe County in the Florida Keys, and two North Carolina counties; Hyde and Tyrrell.

A total cost of $14 trn

The researchers say that the cost of relocating these people could cost the US $14trn (£9.7trn, €12.6trn), if nothing is done to prevent the flooding. This number could be reduced if adaptation strategies are implemented sooner rather than later.

"Adaptation strategies are costly, and these are areas of especially rapid population growth, so the longer we wait to implement adaptation measures the more expensive they become," said Hauer.

The model will help policymakers decide on these preventative measures. Deepak Mishra, researcher working on the study said: "This research merges population forecasts with sea level rise. It gives policymakers more detailed information to help them assess how sea level rise will affect people and infrastructure."