Sea Level Rise Scenarios Compared to the Period 1890 - 1999

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

Since 1992, global average sea level has been calculated and updated every 10 days from the TOPEX/Poseidon (T/P) satellite and the JASON satellite from 660 South to 660 North (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, of which a significant part was due to changes in coastal areas. southern.

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

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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 about 0.70 C , and sea level has risen about 20 cm. The El - Nino and La - Nina phenomena are increasingly having a strong impact on Vietnam. Climate change has actually made natural disasters, especially storms, floods, and droughts, more and more severe. According to calculations, the average temperature in Vietnam may increase by 3 0 C and sea level may rise up to 1 m by the year 2100.

According to the World Bank's assessment, Vietnam is one of five countries that will be seriously affected by climate change and sea level rise, of which the Red River Delta and Mekong River Delta will be flooded the most. If sea level rises by 1 m, about 10% of the population will be directly affected, with a loss to GDP of about 10%. If sea level rises by 3 m, about 25% of the population may be directly affected and harmed

The loss to GDP is up to about 25% about 40 thousand km 2 of Vietnam's coastal plain

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 situation of climate change in Vietnam

- Temperature: Over the past 50 years (1951 - 2000), Vietnam's average annual temperature has increased by 0.70 C. The average annual temperature of the last 4 decades (1961-2000) is 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 were all 0.8 higher than the average temperature of the 1940 decade; 0.4; 0.6 o C. In 2007, the annual average temperature in all three places was higher.

- Rainfall: in each location, the changing trend of average annual rainfall over the past 9 decades (1911 - 2000) is not obvious over different periods and in different regions: there are periods of increase and there are periods of time. decreasing phase. In Vietnam, the changing trend of rainfall is also very different between regions.

- Sea level: According to monitoring data over the past 50 years at Cua Ong and Hon Dau stations, sea level has increased by 20 cm, consistent with the general global trend in the last two decades ( late XX early XXI). In 1994 and 2007, there were only 15-16 cold air waves equal to 56% of the average for many years. Some of the most recent unusual manifestations of climate change are 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 greater intensity has increased, the storm trajectory has almost shifted towards the southern latitudes and the storm season ends later, many storms have more unusual orbits. .

- Number of drizzly days: in Hanoi has gradually decreased over the past decade and has only decreased by 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 build sea level rise scenarios for Vietnam are low emission scenario (B1 scenario), medium emission scenario average of the group of medium emission scenarios (scenario B2) and the highest emission scenario of the group of high emission scenarios (scenario A1FI). Sea level rise scenarios were developed for seven

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

Table 1.2: Sea level rise according to average emissions scenario (cm)

Area

Source: Ministry of Natural Resources and Environment, 2011

* Risk of flooding

Results of identifying areas at risk of flooding according to rising sea levels show that: If 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 is 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 rising sea levels (% area)

Water level rise (m)

Water level rise (m)

Source: Ministry of Natural Resources and Environment, 2011

Calculation results based on traffic data from the Map Publishing House in 2005 show that if the sea level rises by 1m, the whole country will have about over 4% of the 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 transportation system is most severely affected with about 28% of national highways and 27% of provincial roads. The Central Coastal region's transportation system has nearly 4% of national highways, nearly 5% of provincial roads and over 4% of railway systems affected. In the Red River Delta region alone, about 5% of national highways, over 6% of provincial roads and nearly 4% of railways are affected.

At the same time, according to population data from 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, especially the city of Quang Ninh. Ho Chi Minh City is about 7% and in the Central coastal provinces nearly 9% of the population is affected.

1.2.3. Some effects of climate change on mangrove ecosystems

1.2.3.1. Sea level rise

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 came up with 4 response scenarios of mangrove forests 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 properties of the substrate, salinity, frequency, duration of flooding and other factors will decide that the mangrove community can exist continuously and the lower edge of the mangrove forest will remain in the same location (Figure 1.4A).

b) Declining sea level : When sea level decreases relative to the mangrove forest surface, it causes the mangrove forest to move toward the sea (Figure 1.4B). Mangroves can also expand laterally, displacing other coastal habitats into areas adjacent to the mangroves, at lower elevations above the mangrove surface, and developing favorable conditions. Hydrology (duration, depth and frequency of flooding) is suitable for the establishment of mangrove forests.

c) Relative sea level rise : If sea level increases relative to mangrove surfaces, mangrove trees will tend to move towards the sea and away from the land; Species partitions (ecological succession in the region) tend to move inland to maintain their adaptation time, frequency and level of submergence; Seaward, mangrove trees degrade, tidal creeks expand (Figure 1.4C). For example, in Bermuda, mangroves advancing inland have not kept pace with sea level rise (Ellison, 1993). Mangroves can also grow (expand their distribution) to the forest edges of areas adjacent to the mangroves, which are now at a higher elevation than their current mangrove surface. , develop a suitable hydrological regime.

Environmental pressures affecting mangrove ecosystems due to rising sea levels include erosion, weakening tree root structures and gradually toppling trees, or increasing salinity or changing the duration and intensity of flooding (Ellison, 1993).

d) The process of moving mangroves to the mainland through natural regeneration of seedlings (Semeniuk, 1994). Depending on the capabilities of mangrove species and individual individuals, mangroves can invade new habitats at a rate equivalent to the relative rate of rise in sea level and the slope of the area. adjacent land and the presence of landward obstacles (Figure 1.4D).

A. Fixed sea level does not affect mangroves

B. Changes in mangrove area under the impact of climate change

RNM advances to the mainland

Mangrove forests encroach on the sea but the coast is eroded

C. Changes in mangrove area under the impact of climate change, in case there are no obstacles towards the mainland

Mangroves encroached on the sea but were eroded, encroaching on land and getting stuck between dykes. Eventually the RNM band narrows or disappears

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

There is no change in RNM position

Mangrove forests are advancing inland and aggressively encroaching on the sea

Figure 1. 4 : Four scenarios of mangrove forest response to the impact of sea level rise (Gilman et al., 2007)

1.2.3.2. Change in salinity

Mangrove trees live in the transition zone between marine and terrestrial environments. The impact of ecological factors affects their existence. However, up to now 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 adaptations

climate, soil, water, salinity. Therefore, when relying on a specific distribution area to judge the impact of the environment, it may not be applicable in other regions or cannot infer general properties for 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 where the salt concentration in the water is between 10 - 25 o / oo .

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

Some species of fish sauce are medicinal but grow very slowly. In places where the salinity is too low (<4 o / oo ), there are no longer mangrove trees growing naturally. Mangrove species have the ability to adapt to different salinity zones:

- Types with a wide salt range include:

+ The group that tolerates high salinity (10 - 35 o / oo ) includes some species of fish sauce, dong, dong, da quach, parrot...

+ The group that tolerates moderately high salinity (15 - 30 o / oo ) includes mangroves, parrots, parakeets, tigers... these types 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 page, parrot, acanthus, water crow, trumpet cup...

- Type with narrow salt range:

+ Group of succulent woody plants with high salt tolerance (20 - 33 o / oo ) including white cork and guava.

+ The group of succulent plants with high salt tolerance (25 - 35 o / oo ) includes sea salt, sea buckthorn, and Hainan rosemary.

+ Typical groups of brackish water plants (salinity 5 - 15 o / oo ) include nipa palms, sour cork,

beam roof, sea custard apple, water rattan... They are indicator plants for the brackish water environment.

+ Group of plants tolerant to brackish soil living on shallow land with low salinity (1 - 10 o / oo ) from inland to the moist soil along brackish rivers.

When the salt concentration in seawater changes due to seawater dilution due to melting ice, the saline environment of mangrove trees will change, some species will go beyond the salt tolerance limit and have difficulty growing. develop.

In addition, sea level rise gradually exceeds the area of ​​coastal flooded land, salt water has penetrated deeply into freshwater in rivers and underground water sources. These phenomena are enhanced under the influence of storms, especially

when storms combine with high tides. When sea levels rise, salt water will penetrate directly into rivers. This saltwater intrusion phenomenon is not only a consequence of sea level rise, but also a resonance from changes in river discharge. Changes in water flow in rivers are partly the result of climate change (for example, saltwater begins to infiltrate inland during the dry months when river flows decrease). Rising sea levels will also increase pressure on the aquifer, leading to salinity of the water in this aquifer (Islam, 2004).

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

1.3.1. Economics and biodiversity

Mangrove forests have rich resources in both plants and animals

Plant resources

Mangrove species provide many products with high economic value if exploited properly.

a. Wood and materials

Wood from mangrove trees, parrots, toadstools, and acorns is very hard, smooth, and durable, used to make house pillars, planks, beams, household utensils, bridges, fishing net poles... Wood from miscellaneous trees such as fish sauce, cork , price used to make plywood and pulp. Most houses in the Southern countryside are made of mangrove and parrot wood and roofed with nipa palm leaves. This leaf also makes boat hoods and some other household utensils.

b. Ta nin

Tannin extracted from the bark of mangrove trees, parrots, and eagles has good quality, high ratio, and is used to dye fabrics, nets, and tan leather.

c. Fuel

Mangrove trees were the main source of fuel for coastal people in the past. Mangrove and parrot charcoal has high heat (6,375 - 6,675 kcal/kg) and lasts a long time.

d. Product of industry

Many tree species such as bean sprouts, fish sauce, cork... have soft white wood that makes very good pulp. The respiratory roots of cork are used to make corks, caps, and electrical insulators. The wood is smooth , reddish brown in color, used to carve beautiful statues, and is popular with many people. Nipa palm leaves and skulls are also used as handicrafts.

D. Food, drinks