Abstract
Rising temperatures, rapid urbanization and soaring demand for natural resources threaten deltas worldwide and make them vulnerable to rising seas, subsidence, droughts, floods, and salt intrusion. However, climate change projections in deltas often address climate-driven stressors in isolation and disregard parallel anthropogenic processes, leading to insufficient socio-political drive. Here, using a combination of process-based numerical models that integrate both climatic and anthropogenic environmental stressors, we project salt intrusion within the Mekong mega-Delta, in the next three decades. We assess the relative effects of various drivers and show that anthropogenic forces such as groundwater extraction-induced subsidence and riverbed level incisions due to sediment starvation can increase the salinity-affected areas by 10–27% compared to the present-day situation, while future sea level rise adds another 6–19% increase. These projections provide crucial input for adaptation policy development in the Mekong Delta and the methodology inspires future systemic studies of environmental changes in other deltas.
Highlights
Rising temperatures, rapid urbanization and soaring demand for natural resources threaten deltas worldwide and make them vulnerable to rising seas, subsidence, droughts, floods, and salt intrusion
During the dry season, the pristine Mekong River Basin (MRB) provided two sources of freshwater to the Vietnamese Mekong Delta (VMD): (1) the Mekong River and (2) the Tonle Sap Lake (TSL) that was filled in the wet season and acted as a flood retention area
For the first time, we distinguish the effects of main “drivers of exposure and vulnerability”[30] in a mega-delta and identify that while relative Sea-Level Rise (SLR) impacts salinity in parts of the delta, riverbed level changes are the greatest threat to other parts of the delta
Summary
Climate adaptation studies of a mega-delta require in-depth integration of knowledge from natural systemic response to upstream and downstream climatic and anthropogenic developments. The present work does not include (a) evaporation/ transpiration variations driven by climate change in the 3D deltawide model, (b) variations in monsoon winds in the decades, (c) tidal dynamic variations in response to SLR (more important beyond 2050), and (d) exact morphological response of the system to sediment starvation The latter is an extremely complicated affair as it must combine a sophisticated monitoring campaign (to collect bed composition in depth), derive an accurate account of sediment budget in the delta, including sand mining within and beyond the delta, to be able to carry out a reliable modeling exercise. Future work on exploring these morphological interactions and feedbacks of human water use and management of subsidence, sediment dynamics and SWI holds promise to deepen our system understanding and
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