Long-term alterations of flow regimes of the Mekong River and adaptation strategies for the Vietnamese Mekong Delta

Binh, Doan Van; Kantoush, Sameh A.; Saber, Mohamed; Phương, Nguyễn Thu; Maskey, Shreedhar; Phong, Dang Tuan; Sumi, Tetsuya

doi:10.1016/j.ejrh.2020.100742

Cited by 46 publications

(50 citation statements)

References 44 publications

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“…Comparing records from the mega-dam era to the pre-dam era, amplitude dropped by 7.9% at Kratie; 5.6% at Kompong Cham; 10.6% at Neak Luong; and 8.9% at Chaktomuk. This observed increase in dry-season minima and decrease in wet-season maxima is consistent with studies in other parts of the Mekong Basin (Binh et al, 2020b;Li et al, 2017;Räsänen et al, 2017), demonstrating that the impacts of water infrastructure development are evident within the Cambodian floodplains.…”

Section: Changes To Annual Flood Extentsupporting

confidence: 89%

“…Downstream of the Cambodian floodplains, the VMD will also be affected by the decreased floodpulse. While hydropower dam operations can increase dry season water levels (Dang et al, 2016), the combined effects of local channel incision (Binh et al, 2020b) and irrigation operations will reduce dry season water. Since irrigation infrastructure in the VMD is even more developed than those in Cambodia (Tran and Weger, 2018), the impacts of dry-season extraction is likely to be even greater in the VMD.…”

Section: Wider Environmental Implicationsmentioning

confidence: 99%

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Drastic decline of floodpulse in the Cambodian floodplains (the Mekong River and the Tonle Sap system)

Chua

Oeurng

et al. 2021

Preprint

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Abstract. The Cambodian floodplains experience a yearly floodpulse that is essential to sustain fisheries and the agricultural calendar. Sixty years of data from 1960–2019 are used to track the changes to the floodpulse there. We find that minimum water levels in 2010–2019 have increased by up to 1.55 m at Kratie and maximum water levels have decreased by up to 0.79 m at Prek Kdam when compared to 1960–1991 levels, causing a reduction of the annual flood extent. Concurrently, the duration of the flooding season has decreased by about 26 days (Kompong Cham) – 40 days (Chaktomuk), with the season starting later and ending much earlier. Along the Tonle Sap River, the average annual reverse flow from the Mekong to the Tonle Sap Lake has decreased by 56.5 %, from 48.7 km3 in 1962–1972 to 31.7 km3 in 2010–2018. As a result, wet-season water levels at Tonle Sap Lake has dropped by 1.05 m in 2010–2019 since 1996–2009, corresponding to a 20.6 % shrinkage of the Lake area. In addition to known upstream contributors such as hydropower dams, two anthropogenic causes of the drastic alterations to the floodpulse are identified: irrigation and channel incision. We estimate that water withdrawal in the Cambodian floodplains is occurring at a rate of (2.1 ± 0.3) km3/yr and incision-induced water levels reduction is in the order of (0.43–1.02) m. As the floodpulse is essential for the ecological habitats, fisheries and livelihoods of the region, its reduction will pose major implications throughout the basin, from the Tonle Sap system to the Vietnamese Mekong Delta downstream.

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Section: Changes To Annual Flood Extentsupporting

confidence: 89%

Section: Wider Environmental Implicationsmentioning

confidence: 99%

Drastic decline of floodpulse in the Cambodian floodplains (the Mekong River and the Tonle Sap system)

Chua

Oeurng

et al. 2021

Preprint

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“…Recently, such studies have focused on the wetland systems in the Mekong River delta, Vietnam (Nguyen et al, 2016(Nguyen et al, , 2017Binh et al, 2020), on the low-lying Jiangsu coast, China (Bao et al, 2019a;2019b), and the Yangtze River delta (Ma et al, 2018). For the megacity of Shanghai, which is situated at the Yangtze River mouth, scholars have identified high flood risk in the near future as a key concern (Yin et al, 2020), and evaluated the functioning of the coastal wetlands in flood hazard mitigation (Du et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Wetland Utilization and Adaptation Practice of a Coastal Megacity: A Case Study of Chongming Island, Shanghai, China

Bao

Gao

2021

Front. Environ. Sci.

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Coastal urban areas are faced with risks induced by global warming and sea level rise, which puts pressure on regional sustainable development. In particular, land use adjustment is closely related to climate change for a coastal megacity. Coastal wetlands on the edge of the megacity represent a vulnerable ecosystem and a key area in terms of the resilient adaptation strategy. However, the interrelationship between the development of these wetlands and the megacity’s adaptation practice has not been sufficiently analyzed. From a historical perspective, based on document synthesis and field investigation, we attempt in this study to reveal long-term land use stages and driving factors in association with urban marginal wetlands, with a special reference to eastern Chongming Island, Shanghai. On such a basis, the future adaptation strategy of the megacity is evaluated. The analytical results show that this island has witnessed three periods of time for wetland utilization: traditional land use for salt production, fishery and agriculture before 1950, industrialization with rapid reclamation during 1950–2001, and the land use pattern orientated toward wetland ecosystem protection after 2002. The driving forces include sediment budget on the coast, wetland morphodynamic processes, sea level rise, population growth, and resource management policy changes. Transformation occurred between the wetland utilization stages in response to the changes of these forces. Furthermore, facing future climate change, there are different options of adaptation, e.g., retreatment and adherence. It may not be suitable for coastal cities with a large population to take the first option. It will be suitable for coastal communities to adhere to the location, if solutions to the problems of flooding risk, coastal erosion, and the maintenance of coastal facilities can be found. For eastern Chongming wetlands, as a key experimental area for ecosystem-oriented development in Shanghai, the transformation from the reclamation-oriented utilization toward the protection of wetland ecosystems represents the first step toward the latter option. We suggest that the next steps would be to maintain the ecological niche of the wetlands, to create new approaches to coastal engineering with contributions from the ecosystem, and to provide better ecosystem services.

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“…The increase in water discharge during the dry months (+46%) and subsequent decrease during the wet months (À33%) is acknowledged to be significant at Chiang Saen but less so downstream at Stung Treng (Li et al, 2017). However, other scholars have argued that this phenomenon is observable to as far as Kratie, Cambodia (Räsänen et al, 2017) or even until the Vietnamese Delta (Binh et al, 2020). Therefore, while these studies have indicated that the increase in the dry season flows is arguably clear, the changes during the wet season flow have not been clearly quantified and demand further investigations.…”

mentioning

confidence: 99%

“…Our study provides novel insights in three ways. First, previous scholars (Binh et al, 2020;Li et al, 2017;Yun et al, 2020) have only used measured data until 2016 at the latest so the cumulative impacts of the mega-dams were not as evident. Furthermore, the period from 2016 to 2020 witnessed the operationalisation of the first of the series of LMB mainstream dam commissioned.…”

mentioning

confidence: 99%

River Discharge and Water Level Changes in the Mekong River: Droughts in an Era of Mega‐Dams

Chua

2021

Hydrological Processes

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While 1992 marked the first major dam -Manwanon the main stem of the Mekong River, the post-2010 era has seen the construction and operationalisation of mega dams such as Xiaowan (started operations in 2010) and Nuozhadu (started operations in 2014) that were much larger than any dams built before. The scale of these projects implies that their operations will likely have significant ecological and hydrological impacts from the Upper Mekong Basin to the Vietnamese Delta and beyond. Historical water level and water discharge data from 1960 to 2020 were analysed to examine the changes to streamflow conditions across three time periods: 1960-1991 (pre-dam), 1992-2009 (growth) and 2010-2020 (mega-dam). At Chiang Saen, the nearest station to the China border, monthly water discharge in the megadam period has increased by up to 98% during the dry season and decreased up as much as À35% during the wet season when compared to pre-dam records. Similarly, monthly water levels also rose by up to +1.16 m during the dry season and dropped by up to À1.55 m during the wet season. This pattern of hydrological alterations is observed further downstream to at least Stung Treng (Cambodia) in our study, showing that Mekong streamflow characteristics have shifted substantially in the post-2010 era. In light of such changes, the 2019-2020 droughtthe most severe one in the recent history in the Lower Mekong Basinwas a consequent of constructed dams reducing the amount of water during the wet season. This reduction of water was exacerbated by the decreased monsoon precipitation in 2019. Concurrently, the untimely operationalisation of the newly opened Xayaburi dam in Laos coincided with the peak of the 2019-2020 drought and could have aggravated the dry conditions downstream. Thus, the mega-dam era (post-2010) may signal the start of a new normal of wet-season droughts.

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Long-term alterations of flow regimes of the Mekong River and adaptation strategies for the Vietnamese Mekong Delta

Cited by 46 publications

References 44 publications

Drastic decline of floodpulse in the Cambodian floodplains (the Mekong River and the Tonle Sap system)

Drastic decline of floodpulse in the Cambodian floodplains (the Mekong River and the Tonle Sap system)

Wetland Utilization and Adaptation Practice of a Coastal Megacity: A Case Study of Chongming Island, Shanghai, China

River Discharge and Water Level Changes in the Mekong River: Droughts in an Era of Mega‐Dams

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