Doug Edmonds

Climate change is intensifying tropical cyclones, accelerating sea-level rise, and increasing coastal flooding. Coastal flooding will not affect all environments equally, and river deltas are especially vulnerable because of their low elevations, densely populated cities, and river channels that propagate coastal floods inland. Yet, we do not know how many people live on deltas and their exposure to flooding. Using a new global dataset of 2,174 river delta locations and areas, we show that in 2017 there were 339 million people living on river deltas with 329 million (or 97%) living in developing and least-developed economies. We show that geographically, 88% of people on river deltas live in the same zone as most tropical cyclone activity. Of all the people exposed to tropical cyclone flooding, our analysis suggests 41% (or 31 million) live on deltas. Of these, 92% (or 28 million) live in developing or least developed economies, where lacking infrastructure for hazard mitigation increases their vulnerability. Furthermore, 80% (or 25 million) live on sediment-starved deltas that are unable to naturally mitigate flooding through sediment deposition. The 2019 IPCC special report makes it clear that coastal flooding will increase, and it is essential that we reframe the concept of coastal flooding as a problem that will disproportionately impact people on river deltas, particularly in developing and least-developed countries.