Sea Level Rise Scenarios Compared to 1890

Careful selection of station locations can eliminate the influence of major tectonic activities. Averaging all selected data can yield small errors in global sea level estimates. Sea level changes based on satellite data are measured relative to the center of mass of the earth, and are therefore not affected by geological movements.

Since 1992, global mean sea level has been calculated and updated every 10 days from the TOPEX/Poseidon (T/P) satellite and the JASON satellite from 660S to 660N (Nerem and Mitchum, 2001). Calculations by Cazenave and Nerem (2004) showed a sea level rise of 3.1 ± 0.7 mm/year during the period 1993 - 2003, a significant part of which was due to changes in the southern seas.

Table 1.1: Sea level rise scenarios compared to the period 1890 - 1999

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21st Century Milestones
2020	2030	2040	2050	2060	2070	2080	2090	2100
Low (B1)	11	17	23	28	35	42	50	57	65
Average (B2)	12	17	23	30	37	46	54	64	75
High (A1FI)	12	17	24	33	44	57	71	86	100

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Source: Ministry of Natural Resources and Environment, 2009

1.2.2. Climate change and sea level rise in Vietnam

In Vietnam over the past 50 years, the average annual temperature has increased by about 0.7 0 C, and sea levels have risen by about 20 cm. The El - Nino and La - Nina phenomena are increasingly affecting Vietnam. Climate change has really made natural disasters, especially storms, floods, and droughts, more and more severe. According to calculations, the average temperature in Vietnam could increase by 3 0 C and sea levels could rise by 1 m by 2100.

According to the World Bank, Vietnam is one of five countries that will be severely affected by climate change and rising sea levels, of which the Red River Delta and the Mekong River Delta will be the most severely flooded. If the sea level rises by 1 meter, about 10% of the population will be directly affected, with a loss of about 10% of GDP. If the sea level rises by 3 meters, about 25% of the population may be directly affected and the loss of

The loss to GDP is about 25% of the approximately 40 thousand km2 coastal plain of Vietnam.

The South will be flooded every year, of which 80% of the area in the Mekong Delta provinces will be almost completely flooded.

a. Current status of climate change in Vietnam

- Temperature: Over the past 50 years (1951 - 2000), the average annual temperature of Vietnam has increased by 0.7 0 C. The average annual temperature of the last 4 decades (1961-2000) was higher than the average annual temperature of the previous 3 decades (1931-1960). The average annual temperature of the decade 1991-2000 in Hanoi, Da Nang, and Ho Chi Minh City was higher than the average of the decade 1940 by 0.8; 0.4; 0.6 o C, respectively. In 2007, the average annual temperature of all 3 places was higher.

- Rainfall: in each location, the change trend of average annual rainfall in the past 9 decades (1911 - 2000) is not clear according to different periods and regions: there are periods of increase and periods of decrease. In Vietnam, the change trend of rainfall is also very different between regions.

- Sea level: According to observation data over the past 50 years at Cua Ong and Hon Dau stations, sea level has risen by 20 cm, consistent with the global trend in the last two decades (late 20th and early 21st). In 1994 and 2007, there were only 15-16 cold spells, equal to 56% of the average of many years. Some of the most recent abnormal manifestations of climate change were the severe cold spell that lasted 38 days in January and February 2008, causing great damage to agricultural production.

- Storms: In recent years, the number of storms with stronger intensity has increased, the storm trajectory has shifted towards southern latitudes and the storm season ends later, many storms have more unusual trajectory changes.

- Number of drizzle days: in Hanoi has gradually decreased over the past decade and has been reduced to nearly half (15 days/year) in recent years.

b. Sea level rise scenarios and impacts in Vietnam

* Sea level rise scenarios in Vietnam

According to the Ministry of Natural Resources and Environment, the greenhouse gas emission scenarios selected to calculate and develop sea level rise scenarios for Vietnam are the low emission scenario (B1 scenario), the medium emission scenario of the medium emission scenario group (B2 scenario) and the highest emission scenario of the high emission scenario group (A1FI scenario). The sea level rise scenarios are developed for seven

Coastal areas of Vietnam, including: (1) Coastal areas from Mong Cai to Hon Dau; (2) Coastal areas from Hon Dau to Deo Ngang; (3) Coastal areas from Deo Ngang to Hai Van Pass; (4) Coastal areas from Hai Van Pass to Dai Lanh Cape; (5) Coastal areas from Dai Lanh Cape to Ke Ga Cape; (6) Coastal areas from Ke Ga Cape to Ca Mau Cape; and (7) Coastal areas from Ca Mau Cape to Ha Tien.

Table 1.2: Sea level rise under medium emissions scenario (cm)

Area

Year
2020	2030	2040	2050	2060	2070	2080	2090	2100
Mong Cai - Hon Dau	7-8	11-12	15-17	20-24	25-31	31-38	36-47	42-55	49-64
Hon Dau - Deo Ngang	7-8	11-13	15-18	20-24	25-32	31-39	37-48	43-56	49-65
Ngang Pass - Hai Van Pass	8-9	12-13	17-19	23-25	30-33	37-42	45-51	52-61	60-71
Hai Van Pass - Dai Lanh Cape	8-9	12-13	18-19	24-26	31-35	38-44	45-53	53-63	61-74
Dai Lanh Cape - Ke Ga Cape	8-9	12-13	17-20	24-27	31-36	38-45	46-55	54-66	62-77
Ke Ga Cape - Ca Mau Cape	8-9	12-14	17-20	23-27	30-35	37-44	44-54	51-64	59-75
Ca Mau Cape - Kien Giang Cape	9-10	13-15	19-22	25-30	32-39	39-49	47-59	55-70	62-82

Source: Ministry of Natural Resources and Environment, 2011

* Risk of flooding

The results of determining areas at risk of flooding according to sea level rise show that: If the sea level rises by 1 m, about 39% of the Mekong Delta area, over 10% of the Red River Delta area and over 2.5% of the area in the central coastal provinces are at risk of flooding. The area of Ho Chi Minh City at risk of flooding is over 20% of the area:

Table 1.3: Area at risk of flooding according to sea level rise (% area)

Water level rise (m)

River Delta Hong and Quang Ninh	Central Coast	Ho Chi Minh City	Mekong Delta
0.5	4.1	0.7	13.3	5.4
0.6	5.3	0.9	14.6	9.8
0.7	6.3	1.2	15.8	15.8
0.8	8	1.6	17.2	22.4

River Delta Hong and Quang Ninh	Central Coast	Ho Chi Minh City	Mekong Delta
0.9	9.2	2.1	18.6	29.8
1	10.5	2.5	20.1	39
1.2	13.9	3.6	23.2	58.8
1.5	19.7	5.3	28.1	78.5
2	29.8	7.9	36.2	92.1

Water level rise (m)

Source: Ministry of Natural Resources and Environment, 2011

Calculation results based on traffic data from the 2005 Map Publishing House show that if the sea level rises by 1 meter, about 4% of the country's railway system, over 9% of the national highway system and about 12% of the provincial road system will be affected. For the Mekong Delta region, the traffic system is most severely affected with about 28% of national highways and 27% of provincial roads. The traffic system in the Central coastal region has nearly 4% of national highways, nearly 5% of provincial roads and over 4% of the railway system affected. In the Red River Delta region alone, about 5% of national highways, over 6% of provincial roads and nearly 4% of railways will be affected.

At the same time, according to the population data of the General Statistics Office in 2010, nearly 35% of the population in the Mekong Delta provinces, over 9% of the population in the Red River Delta and Quang Ninh were directly affected, about 7% in Ho Chi Minh City alone and nearly 9% of the population in the central coastal provinces were affected.

1.2.3. Some impacts of climate change on mangrove ecosystems

1.2.3.1. Rising sea levels

In their study, Gilman et al. (2007) studied and evaluated the response of the mangrove ecosystem in American Samoa to sea level rise scenarios and simulated the position of the coastline in the recent period. As a result, they presented four scenarios of mangrove response to the impact of sea level rise (Figure 1.4).

a) No relative change in sea level : When sea level does not affect the surface of the mangrove forest, the nature of the bottom, salinity, frequency, duration of flooding and other factors will determine whether the mangrove community can exist continuously and the lower edge of the mangrove forest will remain in the same position (Figure 1.4A).

b) Falling sea level : When sea level falls relative to the mangrove surface, it causes the mangrove forest to move seaward (Figure 1.4B). Mangrove forests can also expand laterally, displacing other coastal habitats to areas adjacent to the mangrove forest, at lower elevations than the mangrove surface, and developing hydrological conditions (duration, depth, and frequency of flooding) suitable for mangrove establishment.

c) Relative sea level rise : If sea level rises relative to the mangrove surface, mangroves will tend to advance seaward and away from the land; species subdivisions (ecological succession in the area) tend to move inland to maintain their adaptation time, frequency and extent of inundation; seaward, mangroves decline, tidal channels widen (Figure 1.4C). For example, in Bermuda, mangroves advancing inland do not keep up with the rate of sea level rise (Ellison, 1993). Mangroves can also grow (expand their distribution area) to the forest edges of areas adjacent to the mangroves, which are currently at higher elevations than their current mangrove surface, developing a suitable hydrological regime.

Environmental stresses affecting mangrove ecosystems from sea level rise include erosion, weakening of tree root structures and gradual toppling of trees, or increased salinity or changes in the timing and intensity of flooding (Ellison, 1993).

d) The movement of mangroves inland through natural regeneration of seedlings (Semeniuk, 1994). Depending on the capacity of the mangrove species and individual trees, mangroves can colonize new habitats at a rate equivalent to the relative rate of sea level rise, the slope of the adjacent land, and the presence of land-side obstacles (Figure 1.4D).

A. Fixed seawater level does not affect RNM

B. Fluctuations in RNM area under the impact of climate change

RNM enters the mainland

RNM encroaches on the sea but the coast is eroded

C. Changes in RNM area under the impact of climate change, in the case of no land-based obstacles

Mangrove forests encroach on the sea but are eroded, encroaching on land and being stuck between dike works. Finally, the mangrove strip is narrowed or disappears.

D. Fluctuations in RNM area under the impact of rising sea levels and being trapped between irrigation works

No change in RNM position

RNM moves inland and encroaches on the sea strongly

Figure 1.4 : Four scenarios of mangrove response to the impact of sea level rise (Gilman et al., 2007)

1.2.3.2. Salinity changes

Mangroves live in the transition zone between the marine and terrestrial environments. The impact of ecological factors affects their existence. However, to date there is no consensus on the role and level of impact of each factor. A common major difficulty is that mangrove species have a very wide range of adaptation to

climate, soil, water, salinity. Therefore, when relying on a specific distribution area to assess the impact of the environment, it may not be applicable to other areas or it is impossible to infer the general properties of this vegetation.

According to Phan Nguyen Hong (1999), salinity is one of the most important factors affecting the growth, survival rate of species and distribution of mangrove forests. This type of forest grows well in places with salt concentrations in water from 10 - 25 o / oo .

Tree size and number of species decreased at high salinity (40 - 80 o / oo ), at salinity of 90 o / oo only

Some mangrove species survive but grow very slowly. In places with very low salinity (<4 o / oo ) there are no natural mangroves. Mangrove species are able to adapt to different salinity ranges:

- Types with wide salt range include:

+ The group that can tolerate high salinity (10 - 35 o / oo ) includes some species of mam, dang, dung, da quanh, parrot column...

+ The group that can tolerate medium high salinity (15 - 30 o / oo ) includes mangroves, cycads, parasitic cycads, and cycads... These species also live in places where salinity changes a lot during the rainy season.

+ The group that tolerates relatively low salinity (7 - 20 o / oo ) has the following species: parrotfish, water fern, water fern, trumpet fern...

- Type with narrow salt range:

+ The group of succulent woody plants that can tolerate high salinity (20 - 33 o / oo ) includes white cork and guava cork.

+ Group of succulent herbs, tolerant to high salinity (25 - 35 o / oo ) includes sea salt, sea cucumber, Hainan hep.

+ Typical brackish water plants (salinity 5 - 15 o / oo ) include water coconut, mangrove,

Roof beams, sea na, water clouds... They are indicator plants for brackish water environments.

+ The group of plants that tolerate brackish soil live on dry land with low salinity (1 - 10 o / oo ) spreading from the inland to moist land along brackish rivers.

When the salt concentration in seawater changes due to the dilution of seawater due to melting ice, the saline environment of mangrove plants will change, some species will exceed the limit of salinity tolerance and have difficulty growing and developing.

In addition, sea level rise gradually exceeds coastal floodplain areas, saltwater has penetrated deep into freshwater areas in rivers and groundwater sources. These phenomena are enhanced by the impact of storms, especially

when storms combine with high tides. As sea levels rise, saltwater will directly intrude into rivers. This saltwater intrusion is not only a consequence of sea level rise, but also a consequence of changes in river discharge. Changes in river discharge are partly a result of climate change (for example, saltwater begins to intrude inland during the dry months when river flows are reduced). Rising sea levels will also increase pressure on aquifers, leading to saltwater intrusion (Islam, 2004).

1.3. The role of RNM in the context of climate change

1.3.1. Economy and biodiversity

Mangrove forests have rich resources of both plants and animals.

Plant resources

Mangrove species give us many products of high economic value if exploited properly.

a. Wood and materials

The wood of mangrove, cypress, cork, and cypress trees is very hard, smooth, and durable, and is used to make house pillars, planks, beams, household items, bridges, and fishing net poles. Wood of miscellaneous trees such as mangrove, cork, and cypress is used to make plywood and paper pulp. Most houses in the rural areas of the South are made of mangrove and cypress wood and roofed with water coconut leaves. These leaves are also used to make boat roofs and other household items.

b. Tanin

Tannin extracted from the bark of mangrove, cypress, and acacia trees has good quality and high ratio, used to dye fabrics, nets, and tanning leather.

c. Fuel

Mangrove trees were the main source of fuel for coastal people in the past. Mangrove charcoal has high calorific value (6,375 - 6,675 kcal/kg) and is slow to burn out.

d. Industrial products

Many tree species such as price, mangrove, and mulberry... have soft white wood that is very good for making paper pulp. The respiratory roots of mulberry are porous and used to make bottle stoppers, caps, and insulators. The wood of mulberry is smooth, reddish brown, and is used to carve beautiful statues and is popular with many people. The leaves and shells of water coconuts are also used to make handicrafts.

d. Food and drink

Sea Level Rise Scenarios Compared to 1890 - 1999

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