Factors contributing to saline intrusion in the Mekong Delta of Vietnam

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

1

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.

1. INTRODUCTION

affect approximately 5 % of Vietnam’s land area,

11 % of the population, 7 % 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 1 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

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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).

1
2
3

Figure 1. Map of the Mekong Delta of Vietnam and locations of the study areas
(1: An Giang, 2: Can Tho, and 3: Soc Trang)

2. 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
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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.

3. 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 2. Average salinity in the Mekong Delta of Vietnam in 2014

(Measured on Hau River branch of Mekong River Delta of Vietnam)

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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 1 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
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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 3. 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 4. 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
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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 2 0C if accounting for B2, and about 0.5 to 2.6
0
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 1. The scenario of climate
change to temperature: In the end of the 21st
century, the average temperature will increase by

Table 1. 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
1
2
3

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
1
2
3

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
1

Low emission scenario (B1)

8-9

11 - 13

22 - 26

51 – 66

2

Medium emission scenario (B2)

8-9

12 - 14

23 - 27

59 – 75

3

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 2 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
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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 2. Tendency effect of weather extreme events, sea level rise and saline intrusion in the Mekong Delta of
Vietnam

No.

Items

Characteristics

Tendency

1.

Rainfall

Rainy day shorter, rainy season come later with less
rainfall. However, changeable heavy rain in dry season,
occasionally happens at night

Decrease

2.

Persistent heat

High temperature with high solar radiation, long dry
season

Increase

3.

Ocean tide

Freshwater shortage and reducing water flow in
upstream, infiltrating seawater flow into the rivers

Increase

4.

Sea level

Seawater occur into the rivers and lead to far inland,
replacing freshwater

Increase

5.

Saline intrusion

Reduction of flow from upstream, seawater lead to far
inland and shift in water and soil characteristics

Increase

6.

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.
4. 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.

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Saline intrusion is threatening livelihoods and
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An Giang University Journal of Science – 2019, Vol. 6, 18 – 25

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