Implementing an arsenal of adaptation measures could cut those costs to between $60 billion and $63 billion annually by 2050. In comparison, the study estimated annual average losses from coastal flooding to be $6 billion in 2005.
Of the projected losses in 2050, $52 billion is due to economic and population growth. The other $8 to $11 billion is due to sea level rise and land use change. The reason for the range is the study also factored in a slightly more optimistic sea level rise scenario of only 7.9 inches by 2050.
Adaptation would come at a financial cost. Hallegatte puts a price tag of $50 billion annually on helping the coastal port cities included in the study to maintain a “relative risk level.” That level assumes that as city economies grow, the ratio of flooding losses to gross domestic product stays constant with 2005 estimates.
On the ground, that means cities would need to invest in a number of protective measures. Levees offer the main form of defense. However, they also lock in rainwater meaning pumping infrastructure would be needed to make sure cities don’t flood from the inside out. Movable storm barriers that help ensure harbors remain operational similar to Rotterdam’s Maeslantkering and flood monitoring and early warning systems would also on the shopping list of cities looking to adapt to rising seas.
All these efforts don’t completely mitigate the risk, though. “You can make floods rarer and rarer,” Hallegatte said, but even the best adaptation measures can’t ensure they’ll never occur again. This creates a paradox where floods are less likely but when they do occur, they wreak more havoc. That paradox poses a particularly big challenge for countries such as Haiti, which have coastal cities that are big players in a relatively small economy.