Modeling saltwater intrusion risk in the presence of uncertainty

The Mekong Delta is one of the most productive rice-producing regions in the world, exporting approximately one-fifth of the global rice traded annually. Previous studies note that saltwater intrusion is a serious concern, and the intensity of saltwater intrusion is primarily driven by sea level rise, land subsidence, anthropogenic sediment starvation, and upstream hydro-infrastructure developments. However, these studies often rely on scenario-based approaches instead of an integrated approach to assess the possible impacts of saltwater intrusion. Using an integrated hydrodynamic-statistical-economic model, we investigate how and the extent to which these drivers may impact the saltwater intrusion. We also examine the costs and returns of two popular saltwater intrusion control policies, i.e., hard-engineering structural and soft-land use planning. When comparing the baseline scenarios, the findings indicate that anthropogenic forces lead to a four times greater saltwater intrusion intensity than the climate change-induced sea level rise. The results further reveal a 50 % or less chance that annual saltwater-affected areas would exceed 1.93 million ha for the baseline, but the likelihood is highly likely to be 100 % with a sea level rising of 22 cm. Under the combined effects of sea-level rise, land subsidence, and riverbed incision, our model shows that the probability of annual saltwater-affected areas staying above 2.30 million ha is almost equal to one. This finding implies that a large share of the current rice-planted areas of the Delta could be wiped out of production for at least one season a year. The findings show that a combination of hard and soft policies would be a more sustainable and cost-effective strategy to lower the intensity and risks of saltwater intrusion. Therefore, there is an urgent need for better coordination of governance and investments among regions within the Delta and counties in the whole Mekong River Basin.