406 I PART 3 I THE MEKONG EMERGENCY
forces in a given morphological setting, influenced by a large number of drivers. Therefore, salinity intrusion is not only influenced by climate change — as reflected in discharge variation, global sea level rise, evaporation, and precipitation etc. — but also by anthropogenic drivers that modify river discharge and water levels, or the bathymetry and geometry of river and estuarine channels [ Eslami et al., 2019b ]. The most recent scientific findings on salt intrusion in the delta show that anthropogenic riverbed incision, driven by sediment starvation due to upstream impoundments and downstream sand mining, currently outpaces climate change effects by orders of magnitude [ Eslami et al., 2019b, 2021a, 2021b ]. Riverbed-level changes simplify salinity intrusion in the deeper estuarine channels and amplify the tidal range that increases ocean forces in salt intrusion. As well as impacting salinity, tidal amplification exacerbates city flooding in subsiding cities of the VMD and creates a feedback loop that contributes to riverbed/bank erosion. While the VMD is already impacted by climate change, it is the combined and cumulative impact of climate change and “local drivers of exposure
2. Delta Elevation 2.1 A key parameter for the delta’s future The elevation of the land surface relative to mean sea level is an important factor that determines the impact of climatic and environmental changes on life in a delta. Low elevation relative to sea level means increased
and vulnerability” [ Oppenheimer et al., 2019 ] that determine the environmental pathways of the delta over the next decades. This chapter aims to provide a holistic view of the past, present and future dynamics of change in the VMD regarding relative sealevel rise and saline water intrusions, by disentangling the effects of various environmental (sea level rise, natural subsidence, and river discharge anomalies) and anthropogenic (human-induced subsidence and sediment starvation) systems stressors. We exhibit the environmental pathways in the coming decades as they relate to elevation as well as saline water intrusion. For the latter, we show how climate change — through sea level rise and upstream discharge anomalies, extraction-induced land subsidence, and riverbed erosion — influences salinity in delta, developing a range of possibilities for the next 3 decades. Figure 9.2 demonstrates a range of salt intrusion scenarios until 2040. The outcome offers crucial input for effective climate adaptation and anthropogenic mitigation strategies in the VMD.
exposure of the delta, its inhabitants and its economic activities to flooding, salinization, and erosion. Lower elevation decreases resilience of the delta to changes in the environment and exponentially increases the costs of livelihood [ Nicholls et al., 2021 ].
2.2 Accurate elevation data crucial for risk assessment It is imperative to have good estimates of present elevation and the relevant processes
