7 Coastal Flooding

Climate Impact Lab

According to new data on the Human Climate Horizons platform, a collaboration between the Climate Impact Lab and UNDP, increased coastal flooding this century will put over 70 million people in the path of expanding floodplains. Latin America, the Caribbean, the Pacific, and Small Island Developing States (SIDS) are at the forefront, projected to lose significant land and critical infrastructure to permanent inundation.

The extent of coastal flooding has increased over the past 20 years as a result of sea level rise, meaning 14 million more people worldwide now live in coastal communities with a 1-in-20 annual chance of flooding, new data reveals. Continuing our current course of global greenhouse gas emissions (SSP2-4.5) is projected by the end of the century to expand this 1-in-20 floodplain to areas today populated by nearly 73 million people.

New hyperlocal data released today by Human Climate Horizons, a collaboration between the United Nations Development Programme (UNDP) and the Climate Impact Lab (CIL), maps in detail this fivefold increase in susceptibility to flood damage along the world’s densely populated coastlines. The data platform makes it possible to see where sea-level rise impacts may most threaten homes and infrastructure. 

Hundreds of highly populated cities will face increased flood risk by midcentury, relative to a future without climate change. This includes land home to roughly 5 percent of the population of coastal cities such as Santos, Brazil, Cotonou, Benin, and Kolkata, India. Flood risk exposure is anticipated to double to 10 percent of the population by the end of the century.

Many low-lying regions along the coasts of Latin America, Africa, and Southeast Asia may face a severe threat of permanent inundation, part of an alarming trend with the potential to trigger a reversal in human development in coastal communities worldwide. By 2100, climate change is expected to cause the submergence of a significant share of land (>5 percent) in the following Small Island Developing States (SIDS) and Associate Members of United Nations Regional Commissions: Bahamas, British Virgin Islands, Cayman Islands, Maldives, Marshall Islands, Turks and Caicos, Tuvalu, and Seychelles.

At the highest levels of global warming (SSP5-8.5), approximately 160,000 square kilometers of coastal land (an area larger than the territory of Greece or Bangladesh) would be inundated by 2100, compared to a future with no climate change. This includes vast stretches of coastal cities in Ecuador, India, Saudi Arabia, Vietnam, and the United Arab Emirates—host of COP28. With concerted action to reduce global emissions and put the world on track to limit warming below 2 degrees Celsius (SSP1-2.6), 70,000 square kilometers of that at-risk land is projected to remain above sea level.

Climate Impcat Lab (2023) Climate change’s impact on coastal flooding