FLOOD RISK REDUCTION AND CLIMATE CHANGE REPONSES TO RICE PRODUCTION IN THE MEKONG RIVER DELTA OF VIETNAM Le Anh Tuan College of Environment and Natural Resources, CanTho University Research Institute for Climate Change – CanTho University Campus II, 3/2 street, CanTho City, Vietnam E-mail:
[email protected]
EXTENDED ABSTRACT The Mekong River Delta (MD) in Vietnam is the most downstream part of the Mekong River Basin. The Delta receives all the water amounts from the upstream countries before flowing to both the East Sea and the Gulf of Thailand. The Delta is very low and flat, with an average land elevation of about 1.00 – 1.50 meters above mean sea level. The MD is 4 million hectares in size and hosts 18 million inhabitants in 2009, in which 8 millions of labors are counted. Human life, agriculture and aquaculture production, and domestic water supplies in the Delta depend highly on the river water regime. Currently, more than 2.4 million ha are used for agriculture and aquaculture production. Each year, the delta supplies more than 50 percent of the nation’s staple rice and crop food, 80 percent of the total fish production, and 75 percent of tree fruits for domestic and export. Each the rainy season, the flood flow from the main river channels and overland from Cambodia across the MD border. Special in September - October, the extension of flood occupies a large areas of the Long Xuyen quadrangle, the Plain of Reeds, the lands between Tien River and the Hau River and the numerous stream and canal system that flood water flow laterally over to the low areas. The flooded area ranges from 1.2 to 1.4 million of ha in years of low and medium flooding, and around 1.9 million of ha in year of high flooding. Although high floods in the Mekong Delta caused significant loss of life and destruction, but many farmers and scientists do not consider floods in MD as a real disaster. Floods have positive effects and ecological functions. “Living Together with Floods” is a motto of the MD’s people as an integrated solution for adaptation and protection of human life and property, to maintain safe and sustainable housing for local people, and to maintain social security. Floods can be controlled by both structural and non-structural measures depending on the natural and social-economic conditions. In last two decades, the MD farmers have created a way for their flood adaptation with a seasonal temporary dyke, simple called as "Semi-dyke" or "August dyke". The semi-dyke is constructed at the height only keeping earliest flood out and protect crop until harvest finishing. After harvesting, some lengths of the dykes were cut to allow flood water entering the fields and inundate the field during flood season. Such a flood control enables farmers both to hinder polluted earlier flood water, to wash field and to utilize great sources of natural fertilizer brought together flood flow.
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More than the pass ten years, climatic change and sea level rise phenomena have become one of the most socio-economical and environmental problems not only for the MD but also for many places in the world. The change of world climate will threat crop failures, life damage and losses and other critical ecosystem vulnerabilities in Asia and Pacific Ocean region. If the sea level rises 1 meter, the Mekong Delta may be loss 15,000 – 20,000 km2 of land and about 3.5 to 5.0 million of people will be affected (IPCC, 2007), adding more pressure to the livelihoods of people in the delta area (TTK & SEA START RC, 2009). These adverse impacts could affect on water resources resulting a socio-economic and environment crisis chain in the Delta unless predictive and preventive measures are taken. It is a real need to estimate and evaluate the potential impacts of climate change on water use in agricultural ecosystems, special for rice production. The changes of maximum temperature, monthly precipitation distribution and flood duration are main factors affecting rice planting areas and the growth of rice. The change of average temperature in the future seems still available for rice growth but the developing harmful insects due to the increase of temperature may be a serious problem. Sea level rise will consequently make more significantly extended flooding and salt intrusion in the inland areas, which in turn causes damage on rice and crop production. It is projected that the boundary of future flood could expand to wider coverage in the downstream part of the MD. The prediction of vulnerabilities to the rice cropping patterns in the Delta should be done through testing many available weather scenarios. Key words: the Mekong River Delta; climate change; extended flood; rice production; adaptation.
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I. BACKGROUND The Mekong River Delta (MD) is located in the centre of the Southeast Asian region. The Delta is the most downstream part of the Mekong River Basin and it is formed mostly by the alluvium deposition of the Mekong River. The whole Delta covers an area of 5.9 million hectares, including the Eastern part of Cambodia (2 million hectares) and the Southern part of Vietnam (3.9 million hectares). The MD has a very high density river and canal network (Figure 1). The Delta in Vietnam is bordered to the North by Cambodia, to the west by the Vam Co river, to the south by the Eastern Sea and to the west by the Gulf of Thailand. The Delta is very low and flat, with an average land elevation of about 1.00 – 1.50 meters above mean sea level except for some low mountains and hills in An Giang and Kien Giang provinces. Currently, more than 2.4 million ha of natural land are used for agriculture and aquaculture production in the MD of Vietnam.
Fig. 1: Location and hydrological map of the Mekong River Delta The MD is affected by tropical monsoon climate. The average monthly temperature of the MD varies from 25°C - 28°C. There are only two distinct seasons in the Delta: rainy season (from May to October) and dry season (the rest months of the year). The quantitative change of annual average rainfall in the MD is among 1,400 - 2,200 mm. More than 90% the rainfall amount occupies in the rainy season. The Delta receives all the water amounts from the upstream countries before flowing to both the East Sea and the Gulf of Thailand. The Upper parts of the Delta are flooded during the rainy season. Salt intrusion along the 600 km-coast has degraded soil and water quality, compromising the agricultural productivity and livelihoods of coastal communities. In the dry season, extends for 7 months, the amount of water from the Mekong 3
River rapidly decreases causing the saline intrusion deeply to the inland resulting in serious shortage of water supply in many coastal areas. In addition, an area of 2-million ha is covered by acid sulfate soils. These physical characteristics have made a diversified agro-ecological system for the Delta. The MD is a really biggest wetland area of Vietnam and is important for biodiversity conservation Mekong basin (Tuan and Guido, 2007). Due to high seasonal variation with over 90% of rainfall and surface water are concentrated during the flood season from May to November, the great potential for agriculture and aquaculture production in the MD is only exploited if flood is controlled and irrigation in the dry season is improved (Hoanh et al., 2010). The MD hosts 18 million inhabitants in 2009, in which 8 millions of labors are counted. More than 70% labors in the MD are farmers. Historically and practically, the people of the Delta have settled and cultivated the land along the river and canal banks began 300 years ago. Human life, agriculture and aquaculture production, and domestic water supplies in the Delta depend highly on the river water regime. The population of the MD has double over the past 30 years and is estimated to grow by another 30 to 50 per cent by the year 2025 (Mekong River Commission, 2004). Rice and fish are the major food not only for Vietnamese but also for many people in the world. The Vietnamese people call the MD as a biggest "rice bowl" and a full “fish basket” of the country. Each year, the delta supplies more than 50 percent of the nation’s staple rice and crop food, 80 percent of the total fish production, and 75 percent of tree fruits for domestic and export. In average, about 3 – 3.5 million tons of rice and 600,000 - 700,000 tons of fishes are yearly exported from Vietnam to the rest of the world. In 1999, 4.5 million tons of exported rice has recorded. It is planned that, total aquaculture production in the MD can reach the target of 1.5 million tons in 2010 and 2 million tons in 2020. Nevertheless in the current and in the future, the Mekong River Basin is considered as one of the basins of the world affected strongly by climate change and sea level rise. Climate change in the Southeast Asia will create a crisis of water resources in the wide-basin that negative leading the food security, affecting the livelihoods of many vulnerable groups, threatening the ecological particular wetland, depleting biodiversity and creating other fluctuations in socio-economic sectors.
II. FLOOD AND CLIMATE CHANGE THREATS TO THE MD Due to locate in the most downstream part of the Mekong river to the sea, the MD accepts yearly all the water flood volume of the basin. At Phnom Penh, the Mekong River joins with the Ton Le Sap of Cambodia and diverts into two main rivers: Tien and Hau rivers when entering into Vietnam territory. At the middle of the delta, Tien and Hau rivers again divert into 9 branches and flow into the East Sea via 9 river mouths: Tieu, Dai, Ba Lai, Ham Luong, Co Chien, Cung Hau, Dinh An, Bassac and Tran De. The flood season in the Delta starts from July, increases gradually in August-September, and peaks in October before falling in November. About 1.2 to 1.9 million ha of land, mainly in the Long Xuyen quadrangle and the Plain of Reeds, affected by annual flooding by overflow water from the river and overland flood water from Cambodia across the Vietnam border that the inundation may last as long as 3 to 4 months. Flooding flows in September – October are higher 10 times the low discharges of the river that occur between 4
March and April (Figure 2). Heavy floods in the Mekong Delta are happened when having 3 main factors coming at the same time: big flow water volume moving down from the Southern of Lao and the Great Lake in Cambodia, changeable long and heavy rainfall affects in the MD, and the high tidal period appearance from the East Sea. Heavy floods may cause many losses of human life and their properties but they are beneficial to deposit a lot of nutrients for cultivated soil, to wash out the field pollutants and toxics as aluminum and iron dissolve from acid surface soil, to push saline water to sea, to kill pestilent insects, and to supply plentiful fish. An Giang and Dong Thap provinces are suffering complexity provinces of heaviest flood inundated areas in the Delta. In the 20th century, the Delta had 14 high floods recorded as equal to or higher than 4.50 m above Mean Sea Level of Ha Tien Datum, in the years 1904, 1923, 1937, 1961, 1966, 1978, 1984, 1991, 1994, 1996, 2000, 2001, 2002, 2005. Based on Water Warning Level III (i.e. more than 4.20 m at Tan Chau), the MD has exceeded emergency flood conditions 22 times since 1926 – 2006 (Tuan et al., 2008).
Fig. 2: Monthly mean discharge of the Mekong River to Vietnam The Mekong River Delta is a “hot spot” for climate change, which is one of the three most vulnerable deltas on the world (IPCC, 2001, 2007; ADB, 1994; MONRE, 2003; Hanh và Furukawa, 2007; Peter và Greet, 2008; Tuan and Supparkorn, 2009. IPPC (2007) has warned that if the sea level rises 1 meter, the Mekong Delta may lose 15,000 – 20,000 km2 of land, and about 3.5 to 5.0 million of people will be affected. However, above damage estimated data is simple based on the consideration of the natural Delta’s topography and current population distribution only. Other effecting factors as rainfall, upstream floods, storm surges, sea tide,… are not been calculated yet. Future climate projection from regional climate model indicates that the Mekong River Delta region tends to be warmer in the future with longer and drier summertime. Seasonal pattern 5
could be altered under influence of global warming. Moreover, changing in the climate pattern in the upstream region of the Mekong River also affect the flood regime of the Mekong Delta, where the boundary of future flood could expand to wider coverage. In 2009, Southeast Asia START Regional Center (Chulalongkorn University, Thailand) and Research Institute for Climate Change – Can Tho University have collaborated in simulating a regional climate model namely PRECIS for downscaling coarse scale Global circulation models (GCM) to derive climate change scenarios for MD. The scenarios of A2 and B2 are applied on the weather data of period 1980 – 2000 to project the climate images for the period 2030s (TTK & SEA START RC, 2009). The results show that there are many areas of the MD will be impacted as follows (Tuan, 2009): • The highest temperature in the dry season will increase from 33 – 35 °C to 35 – 37 °C (Figure 3). • The precipitation at the beginning of the Summer – Autumn (from 15th of April to 15th of May) will decrease about 10 – 20% in main rice production areas of the Delta (Figure 4). The starting time for the rainy season will be 2 weeks delayed in An Giang, Can Tho and Soc Trang (Figure 5). • However, at the end of the rainy season, the precipitation will increase that threat the rice crop harvest period (Figure 6). The rainfall increasing in August combined with the possible risk of early flood from the upstream may make more the rice production losses.
Fig. 3: Average maximum temperature in MD in 1980s and 2030s (simulated)
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Fig. 4: The decrease in the total precipitation in 1980s and 2030s (simulated) Accumulated rainfall: Median year (10.4 - 105.0 - An Giang) 2000.00
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Fig. 5: Changes in starting time for rainy season, accumulated precipitation in 1980s and 2030s (simulated) in An Giang, Can Tho and Soc Trang.
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Fig. 6: Changes in monthly precipitation in present (1980s) and future (2030s) The result is relatively similar to that by IPCC (2007) that show the tendencies: (i) the global temperature will increase 1 °C during 2010 – 2040 and 3 - 4 °C during 2070 – 2100; (ii) the global precipitation will decrease during 2010 – 2040 while increase during 2070 – 2100 (Figure 7). The model also show the changes in the flooding patterns in the delta during 2030 – 2040 compared to the current status: the flooded area will be extended towards areas of Bac Lieu – Ca Mau (Figure 7). However, the number of flood days in upstream provinces will lessen (Figure 9).
Fig. 7: Changes in temperature and precipitation (IPCC, 2007)
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Fig. 8: Changes in flood maximum depth in present (1980s) and future (2030s)
Fig. 9: Changes in flood duration in present (1980s) and future (2030s) Concerning rice production in the MD, it can be foreseen, in the future: • The changes of maximum temperature, monthly precipitation distribution and flood duration are main factors affecting rice planting areas and the growth of rice. The change of average temperature in the future seems still available for rice growth but the developing harmful insects due to the increase of temperature may be a serious problem. Rice productivity can be damaged by the serious droughts and floods in the future. •
The rice farmers in the Delta will pay more money for water pumping when the precipitation reducing in early of rainy season and increasing in the beginning of the flooding season. That means their income from rice production will be reduced.
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Rice production area, as well as other secondary food crop area, will be narrowed down and affected by climate change and sea level rise that leading the yields and total production will decrease. This will cause the threats to the food security for the nation.
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Rice farmers, shrimp farmers, salt farmers and small agricultural businessmen will be significantly impacted due to the lack of essential nutrient sources, land ownership, financial sources and information assessment for adaptation the climate and flood regime change. As a consequence, resources areas of forest, land, water, wildlife, natural minerals… will be encroached, over exploited and damaged.
As another consequence, there may be migrations of farmers in coastal areas that are seriously impacted by climate change and sea level rise to the urban areas in the North and the West of the Mekong River Delta (such as Chau Doc, Long Xuyen, Dong Thap, Can Tho, Vinh Long, My Tho, Tan An …).This will make damages to the urban planning and society orders. Urban environment will be degraded due to the mechanical increase in the population.
III. FLOOD RISK REDUCTION AND CLIMATE CHANGE REPONSES Recent years, flood is one of priority considered issues in many countries. Losses caused by flood are more and more serious and complex. This increasing complexity is directly proportional to interference of human being to nature by deforestation, improper land-use, and pollution. The complex flood problems of the Mekong Delta require a holistic and integrated management because flood is not only the disaster but also the benefit resources of Mekong people. ‘Living with flood’ have been practiced by Mekong people for long time with many traditional measures according to inundated areas. Understanding both affects caused by and benefits generated from flood is vital for designing an appropriate coping strategy by local people towards ‘living with flood’. Flood risks can be controlled and reduced by both structural and non-structural measures depending on the natural and social-economic conditions. Figure 10 provides some available ways for flood mitigation in the Mekong River Delta. •
Structural measures for flood control include technical works such as constructing flood protection dykes, tidal dams, widening/deepening drainage channels to the sea, raising evacuation of foundations, roads, bridges and flood-prone areas, etc… Since 1996, high dykes have been raised further, especially in many districts in An Giang and Dong Thap provinces. As a result, most farmers have steady year-round rice, fruit and fish crops and landless people have paid employment as well. In many villages, farmers built temporary embankment systems for protecting Summer-Autumn crops out of early floods. Strict full closed dykes were set up in many low and medium inundated areas for actively control floods. Pumping stations were built for irrigation, drainage and water supply.
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Non-structural measures mainly include strengthening the capability of flood reduction: upgrading the hydro-meteorological monitoring network, data processing and modeling, providing mass public communication and education, diversifying the rice-other cropping production calendars, establishing Daytime Childcare Centers or “flood kindergartens”, 10
“health-care boats” to take care of children and sick people during the flood time, raising awareness of risks, swimming lessons, and promotion of the use of life jackets and various types of life buoys.
Living with floods
Structural measures
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Upgrading the hydro-meteorological monitoring network and data processing Building flood protection dykes
Diversifying the crop production calendars
Widening/deepening drainage channels
Finding the solution for children security
Raising evacuation of public infrastructure and housing foundations
Providing mass public communication and awareness education
Fig. 10: Some ways for “Living with floods” in the MD (Tuan, 2007) In last two decades, in the Mekong River Delta of Vietnam, the farmers have created a way to "living with flood" with a seasonal dyke, or temporary dyke, simple called as "Semi-dyke" or "August dyke". It ensures that the flood could not enter the early Summer-Autumn rice fields before harvesting. After harvesting, some lengths of the dykes were cut for flood water entering the fields. A survey done in An Giang and Dong Thap provinces has proved that "Semi-dyke" seem more closed with environment conservation than "Full dyke" solution and they give more benefits than "No-dyke" case (Trung et al., 2008). The survey was carried out at 5 levels including province and district governments, mass organization, commune authority and local farmers. The method based on Participatory Rapid Appraisal (PRA) and Rural Rapid Appraisal (RRA). Full dyke height is designed based on the measured and calculated flood peaks; it ensures the safety for the people's daily activities and cultivation in the whole flood duration. Full dykes have advantages for crop insensitive but it needs a high cost investment and it also brings many troubles manly in the alluvium losses and the water pollution inside the dykes. "Semi-dyke" was built by local labors; it did not need a high cost investment. "Semi-dyke" are simple earth dykes. The top height of the dyke is above 20 cm higher the water level in the field. So, this solution has many advantages: farmers may have 2 rice crops per year; flooding water supply more sediment 11
to soil, kill the insects and improve the water quality inside the fields. Otherwise, semi-dyke is a low investment construction and simple maintain. Farmers can catch the fishes and collect the aqua-vegetable for their food during the flood season. For response the climate change to rice production, some solutions have been suggested by the MD farmers for minimize the negative impacts parallel with maximize the positive impacts of climate change. The adaptation solution can be applied for both short term and long term. For the short term, farmers are adjusting the suitable cropping calendars to cope with the weather variation in each sub-region. The rice – fish, rice – shrimp models or integrated agriculture – aquaculture systems should be applied to regular local micro-climate for reducing the high temperature and the low humility in the air. Fish/shrimp ponds nearby the rice fields are places for water storages. In rice cultivation, improved nutrient and pest control should be wellmanaged. Otherwise, agricultural insurance and rural credit policies should be introduced. Capacity building for climate change awareness and adaptation is necessary to be carried out frequently. For the long term, farmers suggest the agricultural scientists should develop more new farming techniques and agricultural modernization. Agro-Sciences institutes and universities should continue to breed the new rice varieties for heat tolerance, for drought tolerance, for salinity tolerance, and for submergence tolerance. Land use planning for climate change adaptation has to considered and adjusted. Furthermore, other agricultural and rural development policies as profession diversification and employment opportunities for farmers should be promoted. Otherwise, natural disaster warning systems have to build in the flooding and coastal areas.
IV. DISCUSSION AND RECOMMENDATION The poor people and farmers in the MD have contributed really a huge food volume for the country but they are the most vulnerability group in the variation of flooding regimes and the change of climate. It is strongly affirmative that the socio-economical development in the Delta is so closely constrained by its water resources regime. Additional challenge, climate change and sea level rise in the Mekong Region will threat the sustainability development of the agriculture and aquaculture production. The “Living with floods” motto, theoretical and practical perspectives, will be enlarged into “Living with climate change”. It is recommendation to consider the activity effectiveness of structural and non-structural measures in the new situations of climate change. The human behaviors on flood risk reduction and climate change response in the Mekong River Delta are needed to analysis in each case of the local socio-economical development plans. There is an urgent need for research on climate change and trans-boundary water cooperation and environmental problems, rather than only technical problems. This is a critical issue that regional and national planners, policy makers, academic scientists, businessmen, local officers and people in the Mekong River Basin have to be aware of.
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