by A coastal river delta with about half a billion inhabitants is precariously situated between rising sea levels and pressure from upstream. These regions have played an important role in the development of society since the last ice age, offering flat fertile lands with an abundance of fresh water suitable for agriculture.
In recent years, coastal river deltas have become hubs of global shipping trade, giving rise to fast-growing megacities such as Dhaka, Cairo and Shanghai. But these areas are now under threat. And not all of the blame can be placed on climate change.
Our recent research shows that 49 deltas worldwide, including the Nile, Mekong, and Mississippi face increasing risks under each of the IPCC’s future scenarios for climate change and development.
Our analysis shows that certain risks are more critical for some deltas than others. These risks include land subsidence, increased population density, intensive agriculture, ineffective governance and lack of capacity to adapt.
Depreciated land
Sea level rise and related impacts, such as salinization, are a major threat to the deltas. But it’s not just the rising sea that creates such risks – the deltas themselves are sinking. Our results show that land subsidence occurs three times faster than sea level rise in deltas such as the Mekong in Vietnam and the Krishna and Godavari in India.
All the land rises and falls as the Earth’s crust slowly changes shape. But, when the land consists of piles of sediment hundreds of meters deep, as in some deltas, the process can happen much faster. The sediment particles compact together under the weight of everything on top (including cities), and when the water, or sometimes oil and gas, that naturally fills the spaces between particles out, the grains fall on top of each other.
Land subsidence (the combination of sea level rise and land subsidence) results in a relative rise in sea level. This process can render cropland solely saline, cause widespread flooding and, in extreme cases, the loss of entire coastal areas. Research suggests that around 25% of Indonesia’s capital Jakarta, which is built on low-lying land near the sea, will be under water in 2050.
Population density and crop land use
The Nile, Ganges and Pearl deltas are also the most densely populated places in the world. China’s Pearl delta, in particular, is encompassed by the major cities of Guangzhou, Dongguan and Foshan, which together are home to over 30 million people. Many deltas will become more densely populated and urbanized in the coming years.
Urban development prevents the natural processes of river flooding from delivering sediment to the delta and maintaining the height of the land above the river channel and the sea. This can submerge delta land relative to sea level at an even faster rate.
Deltas are also very important for food production. Almost all of the red deltas in Vietnam, the Po in Italy and the Yangtze in China have irrigated agriculture. If groundwater is pumped from aquifers to irrigate crops, then these deltas will disappear much faster.
Disturbed food production in these places could have dire consequences in the future – and not just for delta residents. Vietnam is the second largest exporter of rice in the world and almost all of that rice comes from the Mekong delta.
Ability to adapt
Delta countries have options for managing many of the risks they face – not just at the mercy of major global emitters of greenhouse gases. However, the readiness, capacity and effectiveness of governments to adapt to risks is low in many deltas.
This is particularly true of the Irrawaddy delta in Myanmar and the African delta including the Congo, Limpopo and Zambezi. The GDP per capita of the countries in these deltas is one of the lowest in the world, along with indicators of government effectiveness and readiness for adaptation.
International support and cooperation can and should play a supportive role here. But this is not a simple task. Developing countries require a significant amount of funding to implement necessary adaptation measures. In fact, the adaptation finance needs of developing countries are now ten to 18 times the size of international public finance flows (funds that are typically transferred between countries with the aim of supporting development).
And that’s just to adapt to climate change. The range of delta risks revealed by our analysis extends far beyond climate and requires coordination from local to global scales.
What is the solution?
Solutions must be developed that consider all these risks. Efforts to limit climate change, such as controlling groundwater and fossil fuel extraction from deltas, remain urgent.
Cities can be designed to be more resilient to flooding, and agricultural practices can be adapted to deal with risks. This may involve adopting methods such as aquaculture, cultivating salt-tolerant crops, or investigating alternative farming methods that can accommodate floods and delta sedimentation processes.
Read more: Climate change is making soils saltier, forcing many farmers to find new livelihoods
Engineering solutions, such as sea walls, will be required where other strategies are impossible. But these should not be the default approach. Above all, the development of solutions must be inclusive, involving not only experts but local people, fueled by much-needed government action and finance.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Murray Scown receives funding from the Swedish Research Council for Sustainable Development (Forms).
Frances Eleanor Dunn does not work for, consult with, share in, or be funded by any company or organization that would benefit from this article, and discloses no affiliations relevant beyond her academic appointment.
