Introduction.


After 7,500 years of natural fast increasing land accretion (current size: 41,000 km 2 ) and steady propagation to the southeast, this trend has been reversed in the years 2005 to 2018. Climate change is leading to rising sea levels, and according to studies, 38% of the Mekong Delta could be underwater by the year 2100. More than 50% of the 720-kilometre coastline is eroding – of which more than 10% is eroding at between 20 and 50 metres per year. The loss of forest land along the coast is particularly sensitive since this green belt was once stabilising the dynamic silty coasts by attenuating wave surge and trapping fine sand and clay. Erosion of the entire tidal mudflats leave deep scours and steep embankments where natural mangrove resettling is impossible. The current sea-dyke system is hardly able to cope with storm surges and rising waters once exposed to the sea without dyke foreland and mangroves. The sea-dyke system shows many gaps and was never constructed to deal with the current harsh conditions in exposed areas. Dyke breaches and flooding threatens the densely populated hinterland.


In this context, the continuous degradation of ecosystems is only one problem. Another grave threat is the likelihood of an extreme weather event, especially major storm floods and droughts. In case of such a storm flood, large amounts of water could flow over the dykes at different places and form one large water expanse reaching 20-30 kilometres inland, with no way to drain off. Such an event would add significantly to the salinization of the soil, subjecting large areas of the coastal delta to a brackish environment and destroying vast parts of agricultural harvests, putting the livelihoods of tens of thousands of farmers at risk. Peak flows and river floods are set to increase in the wet season. Decreases in dry season flows lead to serious fresh water shortages. Apart from climate change, socio-economic development to a large extent determines the everincreasing pressure on land and water resources even more. In a region where one rice field and shrimp pond borders the next, the loss of land to the sea by erosion means that economic and social pressures multiply. Viet Nam, having transitioned to a lower middle-income country, needs to sustain its growth rates and ensure economic momentum. Developing an appropriate strategy to mitigate and adapt to these changes has become crucial.