CHAPTER 9 I A QUESTION OF WATER I 429
tal pathways in the second half of the century. The effect of land subsidence is more local, and especially impacts the coastal provinces that are already experiencing salinity. Assuming a stable water-/coastline, its impact on the aggregate areas affected by salinity is
5. Main conclusions and policy implications This report integrates the effects of climatic and anthropogenic drivers of change within the Mekong Delta. It addresses in detail the past, present and future dynamics of two main trends: 1 ] elevation loss (land subsidence + sea level rise) and 2 ] increased salt intrusion in the surface water system. Under existing rates of sea level rise (~3 mm/ year) and climate scenarios, current rates of domestic anthropogenic groundwater extraction-induced land subsidence (~10–40 mm/ year, spatially varying) exceed the impact of global climate change. Depending on the policy development and enforcement, as well as the sea level rise acceleration rates towards second half of the century, a large part of the delta’s sub-aerial surface may descend permanently below mean sea level. Furthermore, the effect of current climate change impact on increased salt intrusion has been shown to be limited. In the first half of the century, the increased river discharge during the dry season can partially counterbalance salt intrusion, especially in the estuarine channels. However, in coastal pro-
expected to be limited. Note that the decelerated all-drivers increase in salinity between 2040–2050 is mainly due to the assumption that riverbed levels will stabilize beyond 2040 (see Eslami et al. 2021b for further detail).
vinces distant from the river, salinity will still increase (0.1 PPT/year). While land subsidence marginally impacts salt intrusion in the surface water, sediment starvation — driven by upstream hydropower development and sand mining (within and beyond the delta), resulting in riverbed level incisions — has been the biggest driver of increased salt intrusion over the past decade, and will perhaps continue in the first half of the century. By our best estimates, we conclude that in the next three decades, environmental change in the delta will be dominated by human-induced activities and the exploitation of natural resources (sand and water). However, depending on the state of human activities in the next two decades, from the mid-century on global climate change and [potentially] accelerated sea level rise may become the main agents of change. Therefore, adaptation and mitigation policies in the coming decade are fundamental to the fate of the delta’s livelihood and the cost of adaptation to climate change.
5.1 Main conclusions uThe VMD is subject to various drivers of change, of which the anthropogenic drivers — namely hydropower dams, sand mining, land-use change, and groundwater extraction — pose the greatest threats in the first half of the century, while climate change
