The human-induced activities and influences, plus the increasing climate change threats, are contributing to the risk and exposure of coastal deltaic populations to natural hazards.

Currently, approximately 85% of the world’s largest deltas are diminishing.  Hence, because of reducing sediment supplies caused by the catchment fluxes such as by the upstream and middle stream on hydropower and non-hydropower dams constructions.

Also, the channelisation and aggregate mining activities. These changes undermine the natural ability of the geomorphological dynamics of the nature of deltas. These effects may cause increasing in coastal flooding, river and pluvial (especially monsoonal) on compound flooding. These facts may also escalate riverbank and coastal erosion, causing further vulnerability to the exposed deltaic coastal populations.

For example, 90% of the world’s exposure to flooding is experienced in south and southeast Asia. The Yangtze, Pearl, Chao Phraya, Mekong and the Ganges–Brahmaputra–Meghna (GBM) deltas, as the five Asian mega-deltas (5AMDs), are the largest and most populous of these deltas, housing over 400 million populations (Fig. 1), which equates to approximately 80% of the global deltaic population.

Despite experiencing similar natural hazards, the 5AMDs adopted various deltaic and disaster-management approaches, owing to different paces of the development stage and steps, also because of the governance causes of the deltas.

For example, the Yangtze and Pearl deltas have densely populated urban centres, which relied heavily on engineered structures such as embankments, flood gates and channelized river networks to mitigate flood risk.

In opposite, agricultural-dominated GBM and Mekong deltas, engineered structures are being increasingly used for disaster risk management,  and traditional measures such as earthen embankments and bamboo riverbank protection structures continue to prevail. The Chao Phraya Delta in Thailand is roughly in the middle of this development niche. In short, all 5AMDs are developing and implementing long-term solutions to mitigate and adapt to climate change (see Figure 2). 

In this Review, we illustrate the common challenges and transferable lessons for adapting to natural hazards across the 5AMDs.

First, we highlight the key current hazards that prevail in the 5AMDs, as well as the main future risks. Then we investigate the distinct managerial practices to determine the efficacy of different resilience-building approaches to climate change adaptation, for example, the Sponge City Program (SCP) in China (see Figure 3).

Next, we identify transferable solutions, focusing on the national and municipal levels of current flood resilience and climate policies. Finally, we recommend practices to improve coastal climate resilience in these globally important mega-deltas.

This Review provides an initial exchange of knowledge and practices for delta management at a regional scale. The lessons and recommendations made are not only relevant to the 5AMDs but also to other deltas facing similar challenges, interventions, combined with the growing impacts of climate change, are exacerbating the exposure of coastal deltaic populations to natural hazards.

These changes undermine the natural ability of the deltas to persist above sea level and can lead to an increase in the compound (combined all these floods - coastal flooding, river and pluvial (especially monsoonal) ) flooding, and riverbank and coastal erosion, causing setbacks in development across exposed deltaic populations.

 All 5 AMDs are implementing long-term solutions to mitigate and adapt to the challenges of climate change and human-induced challenges. In this review, we embrace all 5AMDs should or might share their experiences. Therefore, they can all develop their long-term more climate-resilient plans to their "fit-for-purpose" decision- and policy-making practices.

For more information - please read and notice our forthcoming paper that will be published in the Nature Reviews of Earth and Environment (NREE) by 4 June 2024 .