TOI reported that Mumbai would lose $6.4 billion and Kolkata $3.4 billion annually, the study published in Nature Climate Change estimated. In the worst case scenario, the world's 136 largest coastal cities could risk combined annual losses of $1 trillion (750 billion euros) from floods by 2050 unless they drastically raise their defenses, the study said.
Growing populations and assets, the changing climate, and subsidence has resulted into increase of flood exposure in coastal cities, the study found.
Average global flood losses in 2005 are estimated to be approximately USD 6 billion per year. Assuming cities improve their protection to contain the flood risk to current levels, and based purely on the projected growth of city populations and the assets accumulated there, the team warned of a nine-fold increase in losses to $52 billion per year by 2050, AFP reported.
However, this figure changes dramatically once climate change induced sea level rise and subsidence is factored in. It increases to between $60 and $63 billion per year.
"With no adaptation (of flood protection), the projected increase in average losses by 2050 is huge, with aggregate losses increasing to more than $1 trillion per year," said the study-a worst-case-scenario.
But even the best protection in the world won't eliminate the risk, said the study. While higher dykes can reduce flooding, the magnitude of losses when they do occur will continue to rise.
"We have more and more people depending on these protections. That means that if we have a dyke rupture, as there are more people behind the dykes, we will have ever bigger catastrophes," Hallegatte told AFP.
Rich cities, many of them in areas more at risk from flooding, can generally afford better defences than poor cities which are over-represented among those that risk the biggest losses, said the study.
According to Hallegatte, the team has calculated that about $50 billion per year would be required to boost flood protection for the 136 cities in the report-"far below" the estimated losses.