The increasing cost of coastal flooding

Infrastructure damage from coastal flooding will cost the world US$14.2 trillion over the next eight decades and affect more than 280 million people, scientists estimate.

Their analyses, published in the journal Science Advances, are based on a scenario of continued carbon dioxide emissions and no flood defences, projecting that the amount of land affected will surge by 48% to more than 800,000 square kilometres.

That’s an increase in area equivalent to the size of France.

Every continent will be affected, with hotspots on coastlines of north America, northwest Europe, northern Australia, New Zealand, southeast Africa, China, India and Southeast Asia, says co-author Ian Young, from Australia’s University of Melbourne.

Impacts of flooding would come from a combination of rising sea levels and more frequent intense storms.

“Climate change and sea level rise pose a substantial risk to coastal areas, exacerbating the adverse impacts of the extreme seas,” says lead author Ebru Kirezci, also from University of Melbourne.

She explains that sea levels have been rising by about three to four millimetres per year, and although this might not seem like much, elevated water levels become a greater threat when combined with major storms.

“What the data and our model [are] saying is that compared with now, what we see as a one-in-a-100-year extreme flood event will be 10 times more frequent because of climate change,” she says.

The team, which includes researchers from The Netherlands, the UK and Germany, applied a range of value analysis methods to develop a time series of global sea levels, combining data from tides, storm surges, waves and average sea level rise.

Using this, they determined the one in 100-year extreme sea levels and corresponding coastal flooding event and translated it into populations and assets at potential risk from episodic flooding, projected to the years 2050 and 2100.

Results showed that about a third of flooding will be caused by sea level rise and the remaining two thirds by tides and storms, costing the world an amount that equates to 20% of its GDP.

Kirezci says the calculations are important for informing policy and actions to increase the resilience of vulnerable coastal areas.

As well as mitigating climate change, she says adaptation and preparation will be critical. This will include building or strengthening flood defences such as dykes or sea walls, retreating from coastlines and installing coastal warning systems.

“Globally, we need to understand that changes of this nature will occur by 2100 and we need to plan how we are going to respond. In particular, significant parts of the third world will be impacted and the humanitarian issues will be significant.”