Factors contributing to saline intrusion in the Mekong Delta of Vietnam

The extremity of salinity occurred in the Mekong River Delta of Vietnam. Consequences of saline intrusion are not only increasing pressure to people’s livelihoods, but also leading to unstable food security. Less rainfall, comprising drought, persistent heat/high temperature and high tide significantly contributed to increased saline intrusion in mid- and downstream areas.

An Giang University Journal of Science – 2019, Vol 6, 18 – 25 FACTORS CONTRIBUTING TO SALINE INTRUSION IN THE MEKONG DELTA OF VIETNAM Nguyen Huu Tri1 An Giang University Information: Received: 23/05/2018 Accepted: 25/08/2018 Published: 02/2019 Keywords: Saline intrusion, Mekong DELTA, climate change ABSTRACT The extremity of salinity occurred in the Mekong River Delta of Vietnam Consequences of saline intrusion are not only increasing pressure to people’s livelihoods, but also leading to unstable food security Less rainfall, comprising drought, persistent heat/high temperature and high tide significantly contributed to increased saline intrusion in mid- and downstream areas The degree of saline intrusion would increase and would be more challenging in the future, when the saltwater infiltrate into the upstream of the Mekong Delta INTRODUCTION affect approximately % of Vietnam’s land area, 11 % of the population, % of agriculture, and reduce GDP by 10 % (Dasgupta, 2007) Climate change impacts in Vietnam are mainly manifested through the sea-level rise, which leads to increase of flood risk from the ocean, particularly during storm surges in recent years The data recorded from tidal gauges along the Vietnam coasts show that sea level rise was at the rate of three mm per year during the period from 1993 to 2008 (MONRE, 2012) It is projected that 74 % of the population of Vietnam and economic activities that concentrate in the coastal plains and river deltas would be most affected by sea level rise (Carew-Reid, 2008; Dasgupta, 2007) Ninety percent of the Vietnamese Mekong Delta’s surface area would be inundated by 2030 (MONRE, 2012), which would place heavy burdens on rural poor communities who are primarily dependent on natural resources for their livelihoods The number of poor people is projected to increase substantially from 21.2 % to 35 % by 2010 (Carew-Reid, 2008) It is worth noting that m rise in sea level would also The saline intrusion in the Mekong Delta of Vietnam occurs during the dry season, especially from January to April since there is no rainfall The lack of rainfall in the dry season coupled with the interactive impacts of the sea and river dynamics gives rise to the saline intrusion (Tri, 2012) At the same time, the weak flow discharge to the sea supplemented by high tide level even pushes the seawater from estuaries deep towards inland and pervades extensively with different salinity concentration (My & Vuong, 2006) According to Tri (2012), the average discharge of the Mekong River is about 6,000 m3/s in dry season From March to April, it is at its lowest, at approximately 2,000 m3/s; this leads to saline intrusion far inland The tide is the main factor affecting the ratio of flow distribution in the Mekong Delta of Vietnam The tide regime of the East Sea is of an unsteady semi-diurnal type with 18 An Giang University Journal of Science – 2019, Vol 6, 18 – 25 two peaks and two lows as well as two flood tides and two low tides in a month The amplitude of the tide is about 2.5 to 3.0 m in March and April (Tri, 2012) When the upstream flow decreases, the tide affects the Mekong River up to 60 – 70 km from its estuaries Additionally, the decrease of downstream flow of the Mekong River in the dry seasons would pose the potential threats for the water-based economy activities in the Mekong Delta, which exacerbates and speeds up the process of salinization in the area This effect will be more serious under the climate change scenario of Vietnam around 2030 The saltwater will cover about two-thirds of the Mekong Delta of Vietnam and infiltrate into the upstream of the Mekong Delta The research was carried out in the Mekong Delta of Vietnam in order to understand how household livelihood is impacted by saline intrusion This research targeted the households living in the vicinity of three Provinces of the Mekong River Delta including An Giang–upstream, Can Tho– midstream and Soc Trang–downstream Specifically, An Giang Province lies deep in the Mekong Delta near the border of Cambodia on the northwest and locates astride the Mekong River as it enters Vietnam from Cambodia Can Tho is in the central and Soc Trang is in the coastal area at the upstream of the Mekong Delta They are the foremost provinces in the delta for the production of rice and aquaculture (Figure 1) Figure Map of the Mekong Delta of Vietnam and locations of the study areas (1: An Giang, 2: Can Tho, and 3: Soc Trang) METHODS AND MATERIALS discussion to recall important events that highlighted the causes of certain problems and how changes occurred a period of the historical impacts of saline intrusion, and the history of the local community Focus group discussion was used to gather general information giving an overview of saline intrusion and its effects on household production and livelihood Participants in a focus group discussion were head of households who are cultivating rice, freshwater aquaculture and integrated rice and fish farming Besides, the timeline was used along with focus group In-depth interviews with key informants aimed to characterize the impact of saline intrusion on household livelihood Different stakeholders are selected for in-depth interviews They are the 19 An Giang University Journal of Science – 2019, Vol 6, 18 – 25 representatives of the local governments and agencies, such as department and Sub-Department of Environment and Nature Resource, Department and Sub-Department of Agriculture and Rural Development, Center for Hydrometeorology After completing data collection, the researcher made content analysis by grouping main and subtitle issues Cross tabulation of all issues is made for better interpretation (Wellington & Szczerbinski, 2007) On-site measurement of water salinity and soil salinity to assess the content of soluble salts in water and soil that damage rice and fish farming They are measured as electrical conductivity (EC) in units of deciSiemens (dS.m-1) Water samples were directly collected from the irrigation channels, and soil samples from the fields of households RESULTS 3.1 Evolution of saline intrusion in the Mekong Delta of Vietnam According to the Southern Hydrometeorology Station (2014), the saline intrusion in the Mekong Delta was influenced by the mainstream reserve flow and tide The tide was the main factor affecting the flow distribution in the Mekong Delta of Vietnam During the dry season, when Mekong River flow decreased, seawater could flow up through the network of waterways and directly affected up to 70 km from the estuarine of the Mekong River Delta The saline intrusion progress that occurred during the dry season about five-month every year (> 4ppt) is indicated by the curves representing the variability of salinity level recorded at research sites along Mekong River Delta of Vietnam (Figure 2) Household survey was carried out to get information about the households using the structured questionnaires The survey encompassed the household background information; a profile of saline intrusion; household livelihood and saline intrusion; livelihood and production activities, occurrence, degree of impacts, kind of impacts facing household To determine saampled size, this research used the sample size of 390 households which calculated from Yamane (1973) formula to satisfy the requirement of household sampling survey Figure Average salinity in the Mekong Delta of Vietnam in 2014 (Measured on Hau River branch of Mekong River Delta of Vietnam) 20 An Giang University Journal of Science – 2019, Vol 6, 18 – 25 Figure 4.2 showed the variability of salinity levels recorded in 2014 at research sites in the Mekong Delta of Vietnam: An Giang, Can Tho and Soc Trang Most importantly, the salinity measured by Southern Hydrometeorology Station (2014) in the Mekong Delta of Vietnam revealed and confirmed the significantly high level at the downstream (Soc Trang) contaminated in midstream and downstream of the Mekong Delta Also, the results from the in-depth interviews in Soc Trang and Can Tho reflected the complexities of saline intrusion in these communes during the last few years There have been less rainfall and resulting drought conditions which resulted in higher saline intrusion Due to the geographical features, the saline intrusion progress on Mekong estuarine is always more complicated than the mainland The extremity of salinity occurred in the Mekong River Delta of Vietnam often fall in April, which marks the end of dry season contributing to the most devastating saltwater intrusion into the mainland Most notably, the salinity measured at three research sites along Mekong River Delta of Vietnam has informed the significantly high level at the downstream In April, at Soc Trang, the average highest water salinity recorded was 18.2 ppt at the estuary zone, but nearby estuary zone was 2.6 ppt inside sluice gate Meanwhile, as compared to the other two research sites (50 km and 80 km far from the estuary), only Can Tho received the average of salinity level at 0.4 ppt Notably, soil and water samples were collected at the field of rice and fish farming where located inside the sluice gate, so the salinity test result was very low The study results showed that salinity of soil and water samples vary in Soc Trang, with the average salinity being 0.9 ppt (max = 7.1 ppt) in soil and 0.8 ppt (max = 2.6 ppt) in water While in Can Tho, the soil was affected by saline intrusion with average salinity as 0.3 ppt (max = 3.4 ppt) without water salinity, the reason was the interaction between the seawater and freshwater line exchange together during tidal flow up and accumulated inland Despite the average salinity was low; the maximum of water and soil salinity was very high In An Giang, the upstream province, no salinity was detected in all soil and water samples These results confirmed that water source for irrigation was salt- 3.2 Factors contributing to saline intrusion in the Mekong Delta of Vietnam The IPCC warned (2007), if sea level rose by m, the Mekong Delta may lose 15,000-20,000 km2 of land, affecting 3.5 to 5.0 million people However, these estimated damage data is are only based on the consideration of the natural Delta’s topography and current population distribution The impacts from sea levels rise will be aggravated by factors such as rainfall, drought, sea tide, air temperature and others that will change with the climate The household surveyed indicated that less rainfall, drought, persistent heat/high temperature and high tide largely contributed to increasing the degree of saline intrusion (Figure 3) These impact factors enhanced the saline intrusion on various levels, but the highest impacts were in the mid and downstream areas Lack of rainfall in the dry season coupled with the interactive impacts of the sea and river dynamics gave rise to the salinity and lead to saline intrusion far inland (Can Tho Climate Change Coordination Office, 2014) Decreased rainfall and less number of rainy days dramatically increased the degree of salinization in the Mekong Delta The annual average rainfall decreased during the past thirty-five years, from about 1,700 mm to 1450 mm per year Less rainfall combined with the freshwater shortage on upstream has contributed to the tendency of saline intrusion deeper into the mainland The statistics showed a decrease in the number of annual rainy day with the temperature higher than 350C and a remarkable increase in the average temperature 21 An Giang University Journal of Science – 2019, Vol 6, 18 – 25 Percentage (%) during the past thirty-six years While the highest daytime temperature remained, the highest temperature at night significantly increased in 1.50C, resulting in an increase in the average air temperature of 0.70C Additionally, most of the household surveyed (68.7%) noticed that the saltwater level has increased up to 20 – 30 cm 100.00 90.00 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 An Giang Can Tho Soc Trang Less Rainfall 68.85 82.84 88.06 during the height of the dry season Also, households involved in the group meetings at Can Tho and Soc Trang also informed that they could not use the freshwater resource on rivers or canals for household’s daily consumption because of the salinity and water quality Persistent Heat 28.69 66.42 59.70 Drought High Tide 62.30 61.94 81.34 8.20 20.15 69.40 Figure Household’s view on impacts contributing to saline intrusion These impacts would be more serious under the climate change scenario of Vietnam 2030 which two-thirds of the Mekong Delta will be infiltrated by saltwater (MONRE, 2009 & 2012) The tide regime was another factor leading to increased salinity further upstream As the average water flow from upstream decreased from about 7,500 to 6,000 m3/s within fourteen years, the lowest flow from the ocean tides increased from about 13,000 to -17,000m3/s (Figure 4) Figure Diagram of yearly water flow changing the 21st century depended primarily on greenhouse gas (GHGs) emission levels Following the recommendations of the IPCC (2007), the GHGs emission levels were arranged from low to high namely: B1, A1T (low emission scenarios), B2, A1B (medium emission 3.3 Saline intrusion in the Mekong Delta of Vietnam in future MONRE (2012) published updated scenarios of climate change and sea level rise for Vietnam The development of climate change scenarios for 22 An Giang University Journal of Science – 2019, Vol 6, 18 – 25 about 0.4 to 1.3 0C if accounting for B1, about 0.4 to 0C if accounting for B2, and about 0.5 to 2.6 C if accounting for A1FI The scenario of climate change to temperature would surely complex in the scenarios of climate change because the persistent heat has the tendency to increase in the future scenarios), and A2, A1FI (high emission scenarios) Using available data on the change of climate and sea level rise during 1980 – 1999 projections were made under each scenario for various geographic areas Those for the Delta are summarized in Table The scenario of climate change to temperature: In the end of the 21st century, the average temperature will increase by Table Synthesized of climate change factors and sea level rise in the Mekong Delta of Vietnam (adapted from the climate change, sea level rise scenarios for Vietnam, 2009) No Scenario Baseline of the 21st century 2020 2030 2050 2100 I Average temperature change (0C) if compared with the period of 1980 – 1999 Low emission scenario (B1) Medium emission scenario (B2) High emission scenario (A1FI) 0.4 0.5 1.0 1.3 0.4 0.6 1.1 2.0 (1.0 - 1.4) (1.9 -2.5) 1.1 2.6 0.5 0.7 II Annual rainfall change (%)) if compared with the period of 1980 – 1999 Low emission scenario (B1) Medium emission scenario (B2) High emission scenario (A1FI) 1.0 1.6 2.8 3.8 1.1 1.7 3.0 5.8 (2.0 - 4.0) (5.0 - 6.0) 3.2 7.4 1.3 1.8 III Sea level rise (cm) if compared with the period of 1980 – 1999 Low emission scenario (B1) 8-9 11 - 13 22 - 26 51 – 66 Medium emission scenario (B2) 8-9 12 - 14 23 - 27 59 – 75 High emission scenario (A1FI) 8-9 13 - 14 26 - 30 79 – 99 The scenario of rainfall: by the end of the 21st century, the annual rainfall will increase about 3.8% if accounting for B1, about 5.8% if accounting for B2, and about 7.4% if accounting for A1FI However, annual rainfall will tend to decrease in the Mekong Delta of Vietnam The rainy season would start later weeks and total rainfall yearly would be decreased about 20% up to 2030 (MONRE, 2009 and 2012) Sea level rise increased completely under the scenario of climate change At the end of the 21st century, the sea level will rise from about 51 – 66 cm if accounting for B1, from about 59 – 75 cm if accounting for B2, and from about 79 – 99 cm if accounting for A1FI The result of judgments to experts concerned that the Mekong Delta of Vietnam could fall into the scenarios of B2 or A1FI because the tendency increase of weather extreme events, sea level and saline intrusion into various ecological zones in the Mekong Delta of Vietnam (Table 2) Also, when asked the ranking of extreme events affecting to production and livelihood of households in the Mekong Delta of Vietnam in 23 An Giang University Journal of Science – 2019, Vol 6, 18 – 25 the future, experts noticed that saline intrusion was highly ranked as compared with the other factors because of saline intrusion will increase and mainly threats in the future if compared the occurrence of saline intrusion in the past and the present Table Tendency effect of weather extreme events, sea level rise and saline intrusion in the Mekong Delta of Vietnam No Items Characteristics Tendency Rainfall Rainy day shorter, rainy season come later with less rainfall However, changeable heavy rain in dry season, occasionally happens at night Decrease Persistent heat High temperature with high solar radiation, long dry season Increase Ocean tide Freshwater shortage and reducing water flow in upstream, infiltrating seawater flow into the rivers Increase Sea level Seawater occur into the rivers and lead to far inland, replacing freshwater Increase Saline intrusion Reduction of flow from upstream, seawater lead to far inland and shift in water and soil characteristics Increase River and coastal erosion Change the physical of soil, water and ecological characters Increase resources and environment It would more challenge if the climate change, sea level rise scenarios for Vietnam in 2100 really took place Through this research, the paper recommends that preparedness and adaptation to the present and future saline intrusion should be considered by all stakeholders at all levels – from the households to communes, provinces, and the government, focusing policies long-term response to saline intrusion in the harmony of provincial and regional levels To sum up, the research results confirmed that the degree of saline intrusion would increase and more challenging in the future due to the contribution of less rainfall, drought, air temperature and upstream freshwater shortage which has speeded up the process of saline intrusion in the Mekong Delta of Vietnam Saline intrusion was a tendency and contained a negative change in the future CONCLUSION RECOMMENDATION AND REFERENCES The increase of less rainfall, drought, air temperature , and upstream water shortage combined human intervention has speeded up the process of saline intrusion in the Mekong Delta of Vietnam This phenomenon has not only the exacerbation in the present but also complexity under the climate change scenario of Vietnam Can Tho Climate Change Coordination Office (2014) Can Tho climate change activities strategy in the period 2015 – 2030 Can Tho City, Vietnam Retrieved November 2015 from website: http://biendoikhihau.cantho.gov.vn/wpcontent/ uploads/2015/05/150526CanThoResilienceactivitiesStratergy-15-30F.pdf Saline intrusion is threatening livelihoods and agriculture production of households in the Mekong Delta of Vietnam as well as natural 24 An Giang University Journal of Science – 2019, Vol 6, 18 – 25 level rise scenarios for Vietnam Updated edition Hanoi, Vietnam My, T & Vuong, N (2006) Saline intrusion trend in river and canal systems and some prevention methods in Ben Tre Province Vietnam and Japan Estuary Workshop 30, Vietnam Southern Hydrometeorology Station (2014) Report on hydrometeorology in the period 2010 – 2014 Ho Chi Minh City, Vietnam Tri, V.K (2012) Hydrology and hydraulic infrastructure systems in the Mekong Delta, Vietnam In chapter III of the Mekong Delta system: Interdisciplinary analyses of a river delta Springer Publishing House Wellington J., & Szczerbinski M (2007) Research methods for social sciences Continuum International Publishing Group, London, UK Yamane, T (1973) Statistics: An introductory analysis, 3rd edition Happer Publishing House, International edition, Tokyo, Japan Carew-Reid, J (2008) Rapid assessment of the extent and impact of sea level rise in Vietnam International Center for Environmental Management (ICEM) Dasgupta S et al (2007) The impact of sea level rise on developing countries: A comparative analysis World Bank Policy Research Working Paper (WPS4136), World Bank, Washington D.C., USA IPCC–Intergovernmental Panel on Climate Change (2007) Climate change: Synthesis report Contribution of working groups I, II and III to the Fourth Assessment report of the Intergovernmental Panel on Climate Change, Geneva, Switzerland MONRE–Ministry of Natural Resources and Environment (2009) Climate change, sea level rise scenarios for Vietnam Hanoi, Vietnam MONRE–Ministry of Natural Resources and Environment (2012) Climate change, sea 25 ... (2014), the saline intrusion in the Mekong Delta was influenced by the mainstream reserve flow and tide The tide was the main factor affecting the flow distribution in the Mekong Delta of Vietnam. .. occurred in the Mekong River Delta of Vietnam often fall in April, which marks the end of dry season contributing to the most devastating saltwater intrusion into the mainland Most notably, the salinity... 3.2 Factors contributing to saline intrusion in the Mekong Delta of Vietnam The IPCC warned (2007), if sea level rose by m, the Mekong Delta may lose 15,000-20,000 km2 of land, affecting 3.5 to