The potential impacts of climate change, sea level rise on the Mekong Delta region in the period to 2050 and the response measures

Le Trinh^[1], Koos Neefjes^[2]

1. Introduction

The Mekong Delta, located at the lower end of the Mekong River Basin, has an area of ​​43,266 km², including 2,450 km² of water surface of rivers and canals, and a population of 17,273,630 people (2019), accounting for 13.06% in terms of area and 17.94% of the population of Vietnam.

The Mekong Delta is the most important agricultural region in the country, providing over 55% of rice production, 70% of fruit production, 56 % of caught fishery production and 70% of cultured fishery production in Vietnam. However, at present, this is an area with limited development, with low per capita income compared to the national average, and the highest rate of net outmigration in the country. The main reasons are the limited investment in development of transport, industry, urban and rural infrastructure, less developed science and technology as well as the adverse impacts of climate change and sea level rise (SLR), increasing drought and saltwater intrusion combining with the decrease in flow and sediments of the Mekong River due to the development of hydropower projects in the upstream countries.
In order to ensure the sustainable development of the Mekong Delta region, adapting to climate change and impacts from upstream in the three years 2019 - 2021, the Ministry of Planning and Investment (MPI) has formulated the Mekong Delta Integrated Regional Planning (MDIRP) for the Mekong Delta Region in the period of 2021 - 2030, with a vision to 2050 with the consultancy of the JV HaskoningDHV – GIZ ^[3].
Because this paper should not be more than 10 pages, it does not cover all of the climate change issues in the Region, e.g. it does not discuss changes in temperature but focuses mainly on the problems of mean sea level rise (SLR) and salinity intrusion in the Mekong Delta. The paper also proposes directions and solutions for response. Detailed impact analysis and proposed response measures are stated in the Strategic Environmental Assessment (SEA) report for the MDIRP[4].

2. Research methods
2.1. Document Collection and Analysis
Most of the documents and research reports on climate change and its consequences for the Mekong Delta, including scenarios on climate change and SLR for Vietnam of the Ministry of Natural Resources and Environment (MONRE), 2016[5] and updated in 2020[6], reports of the Intergovernmental Panel on Climate Change (IPCC)[7], the Mekong River Commission (MRC)[8] and various study papers of Vietnamese, foreign institutes and authors[9] have been collected and analysed.
2.2. Stakeholder Consultation
In order to ensure information and comments on the consequences of climate change and SLR, and propose appropriate response solutions for the Mekong Delta during the research process, 3 major workshops organized by MPI in various provinces with the participation of representatives of ministries, institutes, universities, environmental, water resource and social specialists. In addition, 3 workshops on SEA, including key environmental issues  and climate change with experts were also organized. The comments and suggestions in the workshops were received to correct the comments on climate change, SLR and mitigation solutions.

3. Summary of some findings
From the results of data collection, analysis and consultation, some issues about the trend of SLR and adaptation solutions in the Mekong Delta can be summarized as follows.
3.1. Climate Change and Sea Level Rise Scenarios for the Mekong Delta Region to 2030 with a Vision to 2050
Climate change and SLR scenarios for Vietnam (MONRE, 2020) include scenarios for temperature changes and precipitation patterns. However, in this paper, we focus on the scenarios for SLR and rainfall, and the consequences for the Mekong Delta.
Table 1. Sea level rise according to RCP scenarios for the East Sea Region (Unit: cm)

Scenario	Timelines of the 21st Century
	2030	2040	2050	2060	2070	2080	2090	2100
RCP2.6	14  (8 ÷ 19)	20 (11 ÷ 26)	25 (14 ÷ 33)	30 (17 ÷ 41)	34 (20 ÷ 48)	38 (23 ÷ 55)	42 (25 ÷ 62)	46 (28 ÷ 70)
RCP4.5	12  (8 ÷ 18)	18 (11 ÷ 25)	23 (14 ÷ 33)	29 (18 ÷ 42)	35 (22 ÷ 51)	42 (26 ÷ 61)	48 (30 ÷ 71)	55 (34 ÷ 81)
RCP8.5	14  (10 ÷ 19)	20 (14 ÷ 27)	28 (20 ÷ 37)	34 (23 ÷ 47)	43 (28 ÷ 59)	52 (35 ÷ 72)	64 (42 ÷ 88)	77 (51 ÷ 106)

Source: Bảng 5.2 trong Bộ TN&MT, Kịch bản Biến đổi khí hậu, 2021.

Note:

• The SLR data compare to the sea levels in the base period 1986 - 2005)

The ranges indicate intervals between the 5% and 95% probability levelsSea level rise due to climate change is one of the biggest challenges for coastal provinces of Vietnam, especially for the Mekong Delta. According to the RCP 4.5 scenario, by the middle of the 21st century, sea level will rise by 23cm (14cm÷33cm); By the end of the 21st century, sea level will rise by 55cm (34cm÷81cm). Global emissions reduction pledges according to Parties to the UNFCCC suggest that this scenario is being followed, and a lower scenario is the aim, so as to achieve the targets of the Paris Agreement of no more than 2^oC global warming by 2100 and preferably no more than 1.5^oC. According to the RCP8.5 scenario, in the middle of the 21st century, the sea level could rise by 28cm (20cm÷37cm), and by the end of the 21st century it would rise by 77cm (51cm÷106cm). Vietnam generally takes 1m sea level rise by 2100 as a possibility that is used in planning, which follows the precautionary principle.
The Mekong Delta is at high risk of inundation and flooding. Table 2 shows that: If the mean sea level rises by 100 cm, 47.29% of the region will be below mean sea level and at high risk of being flooded, of which the provinces with the largest area at risk are: Can Tho (55.8 %), Hau Giang (60.85%), Bac Lieu (61.87%), Kien Giang (75.68%), Ca Mau (79.62%). However, sea level rise of 100 cm is only expected after 2100. In 2050 (the last year of the Mekong Delta Regional Plan), sea level rise is expected to be 23 cm (14cm÷33cm). 

Figure 1. Flood risk map for 100 cm sea level rise in the Mekong Delta Region.
Source: MONRE, Climate Change Scenarios, Updated 2020.

Table 2: Flood risk for the Mekong Delta with sea level rise of 50-100cm

Province	Inundation risk in percentage of land surface below mean sea level
	50cm	60cm	70cm	80cm	90cm	100cm
Long An	0,61	1,36	2,85	7,12	12,89	27,21
Tiền Giang	3,79	6,71	12,58	25,23	37,57	47,80
Bến Tre	6,74	10,19	15,11	21,46	27,83	35,11
Trà Vinh	2,29	4,95	11,51	22,22	32,79	43,88
Vĩnh Long	1,31	2,02	3,66	8,28	18,34	32,03
Đồng Tháp	0,36	0,69	0,96	1,28	1,94	4,64
An Giang	0,08	0,13	0,29	0,49	0,90	1,82
Kiên Giang	36,82	48,85	57,18*	66,16	71,69	75,68
Cần Thơ	0,99	2,88	9,97	26,69	44,89	55,82
Hậu Giang	18,83	29,37	38,50	45,88	53,21	60,85
Sóc Trăng	11,32	14,97	20,25	26,91	33,13	55,41
Bạc Liêu	20,08	27,78	36,84	46,31	54,38	61,87
Cà Mau	40,31	48,05	56,81	64,42	73,58	79,62
Average whole Region	14,86	19,69	27,94	31,94	38,80	47,29

Source: MONRE, Climate Change Scenarios, Updated 2020.

However, SLR is compounded by land subsidence, which is a serious problem in the Mekong Delta. A study on land subsidence conducted by INDRA-GISAT (2019) based on inSAR satellite data shows that areas in the Mekong Delta have different rates of land subsidence: During the period 2014-2019 in some locations, the land subsidence rate was over 3 cm/year, in some places, the land subsidence rate was 5 cm/year. This rate is higher than previously measured and modelled rates of subsidence due to groundwater extraction and is more than 10 times higher than the current annual average sea level rise rate[10]. Detailed data and maps on land subsidence in the Mekong Delta by MONRE[11] and other authors[12] are mentioned in the SEA report.
Therefore, the Regional Plan must consider the possibility of a large area at risk of inundation and flooding by 2050. Depending on successful reduction of the rate of land subsidence, there is a possibility that by 2050 there will be 50-80 cm relative sea level rise, compounding actual sea level rise with land subsidence. Sea level rise will enhance the phenomenon of saline water intrusion into the main river branches and canal systems, causing salinization of water and subsoil, changing the nature of natural ecosystems, and adversely affect fresh water supply for daily life, agriculture and services.

3.2. The Potential Impacts of Climate Change, Sea Level Rise and Dam Construction and Operation on the Environment and Socio-Economic Development in the Mekong Delta
Due to the low, flat terrain and high tide influence in the dry season months with low river flow, saline intrusion penetrates deep into the estuary and into the inland canals of the region. This is the largest and most severe saline intrusion area in the country. Saltwater intrusion is increasing due to increasing impacts of climate change and sea level rise. The salinity boundary is 4%0 (g/L) inland to 50 - 55km along the Tien (Mekong) River and 40 - 45km along the Hau (Bassac) River; Most rivers and canals in Ca Mau peninsula have year-round salinity above 10%. Figure 2 below shows the trend of salinity intrusion in the dry season in the Mekong Delta from 1998 to 2016 and 2020 (salinity isoline of 4%o: Maximum salinity for rice cultivation).

       

Figure 2: Diagram of saline intrusion in the dry season in the Mekong Delta 1998 - 2016 and 2020
Source: JV HaskoningDHV Nederland B.V – GIZ, Baseline Report, Feb. 2020.

In recent years, salinity intrusion in the dry season 2015-2016 was the highest. But in 2020 saltwater intrusion increased further: The total flow to the Mekong Delta through two hydrological stations Tan Chau and Chau Doc reduced by 13% compared to the long term average and lower than the total flow in February.. Specifically, with a salinity margin of 4g/L at the Vam Co Dong and Vam Co Tay rivers with a depth of influence of 95-100 km, 15-20 km deeper than the average for many years. 4 - 6 km deeper than the same period in 2016 (the year with the highest level of drought and salinity ever). The Co Chien River has a depth of influence of about 68 km, 24 km deeper than the largest average of many years, about 3 km deeper than the same period in 2016. The Hau River has a depth of influence of about 66 km, about 6 km deeper than the same period in 2016[13].
Soil and water salinization will lead to:
- Lack of fresh water for daily life: increasing the cost of water supply, increasing the exploitation of underground water leading to the depletion of this water source and accelerating the process of land subsidence.
- Lack of fresh water for agricultural production, animal husbandry, freshwater fishery, industry, service.... causing decline in these industries, adversely affecting income, culture and society; increasing poverty, leading to an increase in outmigration and making the Mekong Delta lag behind in all aspects compared to many regions in the country.
- Increased saltwater intrusion affects almost the entire brackish water shrimp planning area. Aquaculture areas in the coastal areas of Ben Tre, Soc Trang, Tra Vinh, Bac Lieu, Ca Mau and Kien Giang are most affected, possibly leading to the risk of disrupting coastal aquaculture development plans. In 2015, the shrimp farming area was damaged about 3,771ha, Ca Mau alone accounted for about 2,700ha. In some localities, there are many models that are assessed as sustainable such as shrimp-rice, extensive shrimp, improved farming is also severely damaged by increased salinity[14]).
-  Soil salinization: reduces crop yield and increases production costs.
- Increasing costs, investment for "salinity control" works have now been a huge investment in the Mekong Delta and will increase the cost of these works for many decades to come.
- Damage to works and equipment due to salty environment.

4. Solutions for response to the impacts of sea level rise and salinity intrusion for the Mekong Delta region
Detailed directions and solutions on climate change mitigation and adaptation have been proposed in the SEA report on the Mekong Delta Integrated Regional  Plan for the period of 2021 - 2030, with a vision to 2050[15]. Below is a summary of some of the main directions and solutions.

4.1. Adaptive Directions and Solutions
The best direction of adaptation to climate change, sea level rise and impacts from the upstream development of the Mekong River, as well as the impact of development within the Mekong Delta, suggested by the MDIRP is “Respect the laws of nature, avoid violent interference in nature; choose a model of adaptation according to nature, being environmentally friendly, biodiversity conservation and sustainable development with the motto of proactively living with floods, inundation, brackish water and salt water; develop scenarios and have solutions to effectively respond to natural disasters such as storms, floods, droughts and saltwater intrusion, with the most unfavorable situations due to climate change and upstream development of the Mekong River". Below is a summary of the current and future adaptation approaches to climate change impacts that have been proposed by the SEA study and the MDIRP.
a. People's Committees of provinces and cities need to develop and implement a Climate Change Response Action Plan (with emphasis on adapting to sea level rise and saltwater intrusion) at the provincial level until 2030 after the National Response Plan is approved.
b. The authorities need to develop and replicate models of agricultural production, aquaculture and technologies to help adapt to saline intrusion and other impacts of climate change.
c. Restructuring the agricultural sector to better adapt to climate change:
- In the freshwater - brackish transition zone: Switching from a situation where access to fresh water is mainly used for rice cultivation to a system of supplying clean brackish water for aquaculture and fresh water for daily life, production and business;
- In year-round brackish-salt water areas (coastal areas): Switch to aquaculture, taking advantage of the benefits of access to the sea and estuaries;
- In year-round freshwater zone: Shifting towards increased flood-holding capacity and operation management allows crop structure to cope with late arrival of floods and water shortages in the dry season.
d. Agricultural production and aquaculture in the sub-regions of the Mekong Delta Region must adapt to the inevitable changes of climate and increased saltwater intrusion;
e. It is necessary to store river flood water, collect and store rain water and surface water throughout the Mekong Delta, store it where possible, to meet the fresh water demand for domestic, industrial and agricultural use at all times.
f. Developing a water management system with irrigation works such as river dykes, sea dykes, culverts, sluice gates, bridges and ship locks in each area, adapt to climate change and impacts of upstream dam construction and economic activities in the Mekong Delta.
g. Irrigation infrastructure must be managed and coordinated throughout the Mekong Delta region, especially in extreme cases. Regional operational management of the entire irrigation system and facility requires the development of rules for dealing with extreme drought and saltwater intrusion, river flooding, storms, and storm surge. Operational management rules that are coordinated across the Region must be established.
h. Research on construction planning and urban infrastructure construction to adapt to the impacts of climate change and SLR.
i. Enhance awareness and knowledge of leaders at all levels of communities about risks and adaptation measures to extreme climate phenomena and SLR.
k. Strengthen cooperation with programs on basin development: hydropower development, fisheries, forests, water use, water quality management, flood control and monitoring, etc. in the Greater Mekong Sub - Region (GMR).

4.2. Mitigation Methods and Solutions
4.2.1. General Directions and Solutions
General solutions on mitigating impacts due to climate change, SLR and saline intrusion were outlined in the Mekong Delta Integrated Regional Planning Report for the period of 2021 - 2030, with a vision to 2050 are summarized below.
a. Develop and implement programs/projects to respond to natural disasters and climate change and green growth, including building saline control infrastructure/works.
b. Focusing on strengthening the dyke system, dredging canals, increasing the ability to actively control floods, combining research on solutions to store flood water in deep flooded areas to serve water supply in the dry season and other purposes.
c. Construction of infrastructure for tidal inundation and saltwater control (not preventing salinity) in estuaries and coastal areas, including river/sea dyke systems connected to roads and tidal control sluices.
d. Building distributed reservoirs to store fresh water and meet the water demand of economic sectors.
e. Building water supply systems for domestic, livestock and industrial purposes in the context of climate change, including the system of transporting raw water from upstream areas to coastal areas and building storage tanks and desalination systems in the coastal areas. non-centralized small-scale water supply plants.
f. Planning and construction of dike and drainage systems in cities, towns and townships to ensure control of flooding caused by floods and high tides, taking into account the impacts of climate change and sea level rise.
g. Prevent deforestation and forest degradation; new planting and protection of forests, especially coastal mangroves.
h. Building an early warning and forecasting system for natural disaster risks including storms, floods, droughts and saline intrusion.
4.2.2. Some Specialized Directions and Solutions
a. Developing infrastructure systems to mitigate the consequences of SLR and saline intrusion
- For fresh water zone:
This area is less affected by SLR and saline intrusion, so it only proposes directions and solutions for proactive flood control, riverbank erosion prevention and water storage and drainage solutions...
- For buffering fresh – brackish water zone:
Completing the system of irrigation works to actively supply water, control salinity and ensure water exchange and pollution control; invest in works to prevent and prevent erosion of riverbanks and canals, works for regulating and dredging canals to actively store water to meet the requirements of socio-economic development; invest in works to transfer fresh water for transitional and coastal areas to serve industrial and domestic water supply;
- For brackish water all year round:
Completing the system of irrigation works to actively supply water, control salinity and ensure water circulation for aquaculture production and aquaculture; ban on exploitation of underground water for aquaculture; invest in building, strengthening and upgrading sea dykes, river dykes, estuary dykes, embankments, embankment systems to reduce waves causing accretion in combination with planting forests to protect sea dykes and coasts; boat anchorages and infrastructure works in combination with evacuation of people to avoid storms and floods; invest in works to transfer fresh water to transitional and coastal areas to serve industrial and domestic water supply; upgrade and build dike systems and drainage systems to protect urban centers, towns and townships affected by tidal flooding; control land subsidence.
b. Managing tides, sea level rise and coastal erosion
(i) Design and implement regional-level operational management and irrigation infrastructure facilities to support production, especially brackish and saltwater aquaculture, and ensure the safety of people and communities; the field before the tide flooded and the sea level rose.
(ii) Completing, upgrading and maintaining sea dykes and sluice gates in accordance with environmental conditions.
(iii) Construction of canals, sluice gates and suitable operation for brackish water and salt water aquaculture in areas inside sea dykes; separating clean water channels and wastewater drainage channels from aquaculture areas.
(iv) Building a system of sluices to control salt and fresh water appropriately on the system of trunk canals, tributaries, dead-end rivers, etc., turning their conduits into a reservoir system that works "moving over time" and rhythm of each tide” to trap the tide, control salinity, and store fresh water.
(v) Rehabilitation, afforestation and protection of the mangrove belt outside the sea dyke, with suitable density and height to reduce tidal waves and storms. Conservation and expansion of mangroves in Mui Ca Mau National Park; in the coastal provinces from Tien Giang to Bac Lieu: to ensure the restoration of the coastal mangrove strip with a width of over 500m in areas that used to be mangroves.
(vi) Establish breakwaters to prevent coastal erosion of the East and West Seas; strengthen measures to deposit sediment and protect sea dykes.
(vii) In high-risk areas: an early relocation and realignment program should be implemented to prevent the consequences of extreme tidal flooding, water surge and the risk of riverbank erosion, seaside.
5. Conclusions
1. It is forecasted that in 2050 about 6 - 7% of the Mekong Delta area will be below mean sea level if the sea level will rise by 23 - 26 cm. In the 22nd century SLR may reach over 0.7 - 1.0m. Although from now to 2050, the increase in sea level will be compounded by land subsidence and continue to enhance saline intrusion into main streams and canals, causing salinization of water and soil, changing the nature of ecosystems in the region and adversely affect the supply of fresh water for daily life, agriculture and services, greatly affecting the environment and socio-economic development.
2. The impacts of climate change are inevitable and increasingly serious, so adaptation to climate change, sea level rise and impacts from development upstream of the Mekong River basin, as well as impacts of development within the Mekong Delta, are required compulsorily for the Mekong Delta. The motto of adaptation with the highest scientific and practical significance is: "favorable development", "actively adapting to floods and droughts", "living with brackish water and salt water".
3. Therefore, authorities at all levels need to study the transformation of production systems in the Mekong Delta; building and replicating models of agriculture, aquaculture and technologies to help adapt to saline intrusion and other impacts of climate change.
4. To mitigate the effects of climate change and sea level rise, authorities need to develop and implement programs/projects to respond to natural disasters caused by climate change, especially building infrastructure systems/works for salinity control, fresh water storage, inundation control, coastal, urban and residential area protection suitable to each environmental sub-zone and each area.
5. Protecting and strengthening afforestation, rapidly increasing forest area, especially coastal mangrove forests, is a particularly important solution that not only improves environmental quality, pollution control and conserves biodiversity, but also to mitigate storm surges and resulting coastal flooding that are enhanced by sea level rise, coastal erosion and land subsidence.

References
1. Báo Điện tử Đảng Cộng sản Việt Nam,12/02/2020.
2. Ministry of Planning and Investment, MDIRP Report, Consultant: JV HaskoningDHV Nederland B.V – GIZ, Nov.2021.
3. Ministry of Planning and Investment, SEA report for MDIRP, Consultant: JV HaskoningDHV Nederland B.V – GIZ, Nov.2021.
4. MONRE, Climate Change for Vietnam, Updated 2020.
5. IPCC, AR5, 2013.
6. JV HaskoningDHV Nederland B.V – GIZ, MDIRP, Baseline Report, Feb. 2020.
7. Mekong River Commision, Website, Climate Change.
 

January 2022.

 

---

[1] Le Trinh, Leader of the SEA Team for the MDIRP.

[2] Koos Neefjes, Climate Change Specialist, International Expert of the Planning Team of the Mekong Delta Integrated Regional Planning for the Period of 2021 - 2030, with a Vision to 2050 (MDIRP).

[3]Ministry of Planning and Investment, MDIRP Report, Consultant: JV HaskoningDHV Nederland B.V – GIZ, Nov.2021.

[4] Ministry of Planning and Investment, SEA Report for MDIRP, Consultant: JV HaskoningDHV Nederland B.V – GIZ, Final Version, Dec.2021.

[5] MONRE, Climate Change and Sea Level Rise for Vietnam, 2016.

[6] MONRE, Climate Change for Vietnam, Updated 2020.

[7] IPCC, AR5, 2013.

^[8] MRC Website, Climate Change.

[9] Viện KH Thủy lợi miền Nam, báo cáo “ĐBSCL trước các thách thức BĐKH, phát triển thượng lưu, lún sụt đất và định hướng các giải pháp thích ứng”, Hội thảo Cần Thơ, 19/11/2020; JV HaskoningDHV Nederland B.V – GIZ, Baseline Report, Climate Change, Feb. 2020.

[10] INDRA-GISAT, 2019 (JV HaskoningDHV Nederland B.V – GIZ, Baseline Report, Feb. 2020).

[11] Cục Quản lý Tài nguyên nước - Bộ TN&MT, Báo cáo về quản lý tài nguyên nước và giải pháp ứng phó với sụt lún khu vực TP. Hồ Chí Minh và vùng ĐBSCL tại diễn dàn "Quản lý tài nguyên nước, lũ lụt, xâm nhập mặn, ứng phó với sụt lún, sạt lở ở vùng ĐBSCL", 18/06/2019

[12] Minderhoud và nnk, 2017 (JV HaskoningDHV Nederland B.V – GIZ, Baseline Report, Feb. 2020).

^[13] Báo Điện tử  ĐCS Việt Nam,12/02/2020

[14] Cục BĐKH - Bộ TN&MT, BĐKH ảnh hưởng xấu đến nuôi trồng thủy sản, 14/12/2017.

[15] Ministry of Planning and Investment, MDIRP Report, Consultant: JV HaskoningDHV Nederland B.V – GIZ, Nov.2021.

Author: Assoc. Prof. Dr. Le Trinh

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