A study published in the journal Science suggests that even rich nations will not be able to spend enough to keep the seas at bay indefinitely and that delta cities will ultimately face major flooding risks.
Population growth, urbanization, and rising sea levels are placing populations living in delta regions under increased risk. The future resiliency and potential for adaptation by these populations depend on a number of socioeconomic and geophysical factors. The authors examined 48 deltas from around the globe to assess changes in regional vulnerability. Some deltas in countries with a high gross domestic product will be initially more resilient to these changes, because they can perform expensive maintenance on infrastructure. However, short-term policies will become unsustainable if unaccompanied by long-term investments in all delta regions.
The research suggests that the Mississippi and the Rhine may become up to eight times more at hazard from rising tides, storm surges or catastrophic downstream floods. The study calculates the challenges ahead for 48 major coastal deltas in the Americas, Europe and Asia, right now home to populations of more than 340 million people.
Deltas are natural sites for cities: they offer direct access to the sea and upriver to the hinterland; their wetlands provided good hunting and, when drained, became fertile farmland, ever renewed by fresh deposits of silt from frequent flooding. So civilization got a head start in the Nile delta, the Indus, the Ganges and the Brahmaputra, the Yangtze, and elsewhere.
But dams upriver to conserve water or generate electricity stopped the downstream flow of silt. The draining of the wetlands allowed the soils to compact. The abstraction of water for industry and for huge numbers of new citizens meant that soils compacted even more. The reclamation of wetlands meant that the highest tides had nowhere to go but on to the streets and into city basements. And the sea began to encroach, which meant more investment in
The researchers found that while 340 million were directly at risk in their 48 major coastal deltas, there were also an estimated 140 million people living within a 25km radius of the vulnerable regions.