Droughts in the Anthropocene

Vietnam – The impact of drought in the Lower Mekong

The Mekong River system supports unique landscapes, rare wildlife and diverse cultures. It journeys from the heights of the Tibetan plateau, through China and Myanmar, before entering the Lower Mekong Basin (LMB) comprising Cambodia, Lao People’s Democratic Republic (Lao PDR), Thailand and Vietnam’s vast delta region. The Mekong Basin is home to around 70 million people, with 60 million located in the LMB [1]. Considered the ‘rice bowl’ of Asia, the basin is of vital importance to food production in the region and the millions of livelihoods it supports. The Mekong River is a nutrient rich system: its flows support sediment transportation vital for ecological health and the flood plain process that supports productivity, particularly in agriculture and fisheries. However, rapid development and a changing climate are altering the Mekong River. The changes imposed by nature, as well as human interventions of land-use change, urban development, dams, deforestation, overextraction of groundwater and riverbed mining, along with climate change-driven extremes such as droughts, are increasing livelihood vulnerability and the pressure on resources in the LMB. Drought is the most significant constraint on the socioeconomic status of the Mekong Basin due to its impact on ecosystem services, with implications for well-being and livelihoods. The drought in 2016 damaged crop production and resulted in losses equal to US$300 million [2]. The current 2019 drought in Vietnam is the worst in one hundred years and consistent with future predictions showing increased probability and risk of drought in the LMB [3]. Increases in the frequency and severity of droughts are compounded by variations in the water cycle caused by changes in the timing and intensity of monsoonal rain and the influence of dams and water extraction. Variations in water availability,

less predictable seasons and higher temperatures have implications for the productivity, food security and health of those living in the LMB. Both natural and anthropocentric climatic changes, combined with water interventions, continue to influence the quantity and timing of water within the LMB. The 2016 drought in the Mekong Delta resulted in the worst recorded salinity intrusion, heavily damaging agricultural land [2]. The reduced flow at the delta mouth, allowed seawater to advance inland, damaging productivity and even rendered areas infertile. Droughts also impact the transportation of sediment, which is further amplified by dams and dykes that inhibit and alter its distribution within the LMB. If all proposed dams are constructed, it is estimated that the sediment load within the Mekong system could be reduced by 96 per cent [1]. The loss of sediment alters the relationship between the sediment deposition and the rate of erosion, leading to a potential increase in the loss of land. Overextraction of groundwater in the Mekong Delta has also resulted in land subsidence that increases the risk of salinization of land and the groundwater. The delta is also extremely low-lying and exposed to erosion from rising sea levels [4]. As a result of the anthropogenic and natural climatic changes, the Mekong Delta’s river flows are becoming increasingly irregular, increasing the challenges faced and holding social, environmental and economic implications. Through multiple initiatives, IHP is assisting in finding solutions to water management challenges within its programmes on groundwater, sediment flows and climate change vulnerability mapping. In 2013, the collaborative project Solution for Groundwater Problems was launched in South Asia. IHP supported the project through its

analysis and defining of the transboundary aquifer systems [5]. IHP also supported cooperation between countries to improve aquifer protection and sustainable use to address the information on shared aquifers and pollution and over extraction issues. Through the Climate change vulnerability mapping for Greater Mekong subregion case study, IHP identified countries within the Mekong basin as being highly exposed to natural hazards such as floods, droughts, and tropical cyclones and associated adverse impacts [6]. Adaptive capacity and vulnerability to the detrimental effects of climate change were mapped, producing a valuable tool for determining mitigation and adaptation measures at the provincial level for disasters such as drought. Lastly, the recent study by the Stockholm Environment Institute and UNESCO looks to support the implementation of the IHP International Sediment Initiative [1]. The study analyses the reduction in sediment within the Mekong River that has occurred at a rate exceeding previous estimations. The study provides a knowledge base in which the implications of reduced sediment on the vital process of nutrient flow, stabilization and formation of deltas and ecosystems and production systems they support can be considered. The reduction has the potential to threaten livelihoods and is a crucial consideration within the broader context of climate change vulnerability and adaptation.

ASIA AND THE PACIFIC

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