Coastal river deltas are threatened by more than just climate change Sciences

Worldwide, coastal river deltas are home to more than half a billion people, providing livelihoods such as fisheries and agriculture, on whose shores cities are built, and providing fertile ecosystems for biodiversity.

In a unique study covering 49 delta regions around the world, an international team of researchers identified the risks that most threaten delta regions in the future. The research shows that delta regions face multiple risks, and that population growth and environmental mismanagement may pose greater threats than climate change to the sustainability of Asian and African delta regions in particular.

Consequences of delta collapse

As a press release from Sweden’s Lund University, which led the study, notes, the collapse of delta environments could have dire consequences for global sustainable development. In the worst-case scenario, delta areas could be lost to the sea. Other consequences of losing delta areas include floods, water salinization affecting agriculture, coastal pressure, and loss of ecosystems.

The study, published in the journal Global Environmental Change, looked at five different IPCC scenarios for global development in 49 deltas around the world, including famous deltas such as the Nile, Mekong and Mississippi, as well as less well-studied deltas such as Deltas of the Volta and Zambezi rivers, and the Irrawaddy Delta.

The research identifies potential risks to the delta areas extending 80 years into the future. The researchers based their analysis on 13 known factors that affect risks in the delta regions, and relied on unique models to determine which of these risks are likely to expose the different delta regions to danger in the future.

Risk factors include increasing population density, urban development, irrigated agriculture, changes in river drainage, land subsidence and relative sea level rise, limited economic capacity, weak government effectiveness, and low readiness to adapt.

The most important risks

The analysis shows that there are some risks that are more important to delta regions than others in all five future scenarios. These factors include land subsidence, relative sea level rise, population density, ineffective governance, economic capacity, and agricultural land use.

For some areas of the delta, the physical risks are particularly evident. For example, land subsidence is the greatest risk factor in the Mekong Delta in Vietnam, while extreme sea levels are among the risk factors of greatest concern for delta areas in China, on the Korean Peninsula, and in the Colorado (Mexico) and Rhine (Netherlands) deltas ).

In the Nile Delta (Egypt), the Niger Delta (Nigeria) and the Ganges Delta (Bangladesh), increasing population density is most worrying under certain scenarios. As for other delta regions, such as in the Irrawaddy Delta (Myanmar) and the Congo (Angola and Democratic Republic of the Congo), the reason is the lack of economic capacity and government effectiveness to manage risks.

Murray Skone, senior associate lecturer at the Lund University Center for Sustainability Studies and lead author of the study, says: “From the analysis we can see that the major Asian delta regions are at greatest risk, with potentially devastating consequences for millions of people and the environment, as they are under pressure from population growth and intensive use.” of agricultural land, relative sea level rise, and delayed readiness for adaptation.

Mitigating risks locally and globally

As the researchers say in the press release, “Rather than sitting idly by, governments should think long-term and develop plans to reduce or mitigate risks. In the Mekong Delta, for example, the Vietnamese government is making strong efforts to restrict groundwater extraction in the delta.” In the future to reduce land subsidence and salinization.

The researchers highlight that a mix of adaptation approaches will be required to manage and mitigate delta risks, which include hard infrastructure such as seawalls to prevent the sea from inundating the delta, and approaches that use nature-based solutions.

An example of this is the Dutch experience in creating space for the river in the Rhine Delta, by reducing floodplains, moving dams, and using areas allowed to flood for grazing. Frances Dunne, an assistant professor at the Dutch University of Utrecht, points out that initiatives aimed at building delta surfaces by allowing rivers to flood and deposit sediment on the delta to maintain the elevation above sea level; It is also considered promising.

“By looking at delta areas together as we did in this study, we want to highlight what could happen on a global scale if we do not address delta risks at the local and global levels,” says Maria Santos, a professor at the University of Zurich. “The study can also complement studies on individual delta areas.