Water, Climate, Food, and Environment in the Mekong basin in southeast Asia Contribution to the project ADAPT Adaptation strategies to changing environments

Final Report June, 2003

Chu Thai Hoanh, Hans Guttman, Peter Droogers and Jeroen Aerts International Water Management Institute (IWMI) Mekong River Commission Secretariat (MRCS) Institute of Environmental Studies (IVM)

Contents 1.

INTRODUCTION.......................................................................................................................................... 2

2.

NATURAL RESOURCES ............................................................................................................................ 4 2.1. 2.2. 2.3. 2.4. 2.5. 2.6. 2.7. 2.8.

CLIMATE ..................................................................................................................................... 4 TOPOGRAPHY ............................................................................................................................. 6 LAND USE .................................................................................................................................... 8 SURFACE WATER RESOURCES .................................................................................................. 10 GROUND WATER RESOURCES ................................................................................................... 13 SOILS ......................................................................................................................................... 13 ENVIRONMENTAL ISSUES.......................................................................................................... 14 SOCIO-ECONOMIC CHARACTERISTICS ..................................................................................... 15

3.

INSTITUTIONAL ARRANGEMENTS .................................................................................................... 19

4.

PROJECTIONS FOR THE FUTURE ....................................................................................................... 20 4.1. POPULATION, WATER AND FOOD ............................................................................................. 21 4.2 CLIMATE CHANGE SCENARIOS FOR THE MRB.............................................................................. 23

5.

MODELING ACTIVITIES ........................................................................................................................ 33 5.1. 5.2.

6.

IMPACTS AND ADAPTATIONS ............................................................................................................. 35 6.1. 6.2. 6.3

7.

SWAP MODEL FOR FIELD SCALE FOOD PRODUCTION ............................................................ 33 SLURP MODEL FOR BASIN SCALE ........................................................................................... 33 ISSUES AND INDICATORS ........................................................................................................... 36 ADAPTATION STRATEGIES ....................................................................................................... 38 EVALUATION AND PERFORMANCE OF ADAPTATION STRATEGIES ........................................... 39

CONCLUSIONS .......................................................................................................................................... 45

REFERENCES ...................................................................................................................................................... 47 APPENDIX A ........................................................................................................................................................ 50 APPENDIX B......................................................................................................................................................... 51 APPENDIX C ........................................................................................................................................................ 52

Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

1

1. INTRODUCTION The Mekong is one of the world’s largest river basins1 (IMC, 1988a) with an area just under 800,000 km2 and is shared by six countries; China (Yunnan Province), Union of Myanmar, Lao PDR, Kingdom of Thailand, Kingdom of Cambodia and Viet Nam (Figure 1). The basin is the home for over 65 million inhabitants (MRC and UNEP, 1997). During the last 10 years, several studies and projects have been carried out for achieving cooperation among the six riparian countries in planning and promoting regional economic development in the Greater Mekong Sub-region (GMS) (ADB, 1999; Nilsson M. and L. Segnestam, 2001). However, the Lower Mekong River Basin (LMB), covering 77% of the Mekong River Basin (MRB), is regarded as the most important part of the Mekong basin, both environmentally and economically. It is, therefore, the focused area of the Mekong River Commission since 1957 (Mekong Committee, 1970; IMC, 1988a; Hori, 2000). The population in LMB is largely rural and most people are employed in agricultural or related activities, with rice as major crop. All countries in the LMB have ambitious plans to maintain or increase national food production in the basin area, with particular emphasis on increased dry-season Figure 1: Location of Mekong River Basin. food production, agricultural diversification and expansion of fish production (aquaculture and capture fisheries). As such agricultural production is one of the five key areas of natural resources and development in the region (Nilsson and Segnestam, 2001), the other areas being hydropower generation, fisheries, forest resource management, and the use of biological resources for conservation, tourism, trade and local livelihoods. In the LMB, the livelihoods of people are dependent on its waters and the services provided by surrounding environment. However, this is changing due to rapidly growing and potentially conflicting demands, on the water and land resources. Although the Mekong riparian countries enjoy abundant water resources, availability varies widely by region and by season, due to the monsoon rainfall pattern. Competition for scarce water resources is particularly evident during the dry season, when water flows into the Mekong Delta can be as low as 2,000 m3/s (December-March), compared to an average flow of 25,000 m3/s during the rainy season (July-November). In general, water resources in the MRB as a whole are not highly developed. However, there are several emerging issues regarding water usage in the MRB: (i) irrigation development in Northeast Thailand has resulted in a lack of water during the dry season and restricts the amount of dry season cropping At some 4800 km in length and an annual flow of 475,000 million m3 it is the world’s twelfth longest and tenth greatest respectively (IMC, 1988a).

1

Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

2

possible; (ii) intrusion of saline water to the Mekong Delta in Vietnam depends on the magnitude of the dry-season flows from upstream and the level of abstractions for irrigation in the delta; (iii) the floods2; (iv) hydropower development, built or proposed, with distribution of benefits across countries and sectors not thoroughly evaluated; (v) finally, growing populations and increasing economic development is starting to affect water availability negatively by degrading the water quality (MRC 2001). The Intergovernmental Panel on Climate Change IPCC (2001) recently concluded that the climate has changed during the 20th century and larger changes are projected for the 21st century; such change will have both beneficial and adverse effects on both environmental and socio-economic systems, but the larger the change and the rate of change in climate, the more adverse effects predominate; adaptation is necessary and its costs can be reduced by anticipation, analysis and planning. In a special report of the IPCC (1997), the main regional impacts of climate changes in the MRB are: • As a result of the seasonal shifts in monsoon weather patterns, a large part of Tropical Asia, including the MRB, is exposed to increased annual floods and droughts. • Increased number of Tropical Cyclones • Other extreme events include high-temperature winds. • In the megacities and large urban areas, high temperatures and heat waves will frequently occur. These phenomena are exacerbated by the urban heat-island effect and air pollution. • Geographically much more extensive is the El Niño-Southern Oscillation (ENSO) phenomenon, which has an especially important influence on the weather and interannual variability of climate and sea level, especially in the western Pacific Ocean and South China Sea around the MRB. Therefore, the MRB was selected as one of seven pilot river basins for the ADAPT project3. The main objective of the ADAPT project is to assess impacts of climate change and climate variability on food production, food security and the environment (ecological and social) and develop adaptation strategies to alleviate the negative impacts on food and environment. The activities of the Mekong case study are described in this report, and can be summarized as: (i) Describing the current status of water resources and related socio-economic aspects for the MRB, with a focus on the LMB (ii) collect existing climate change projections (GCM results) for the basin from IPCC datasets and compare historic weather data with GCM results for the same period and adjust, if necessary, GCM results; (iii) select a simulation model at basin and field scale to simulate potential hydrological and food production changes (iv) assess the state of environment and food security related to water resources under present conditions and climate change (v) define and assess adaptation strategies to alleviate impacts of climate change.

2

The flood in 2000 was the highest flood in over 40 years in some areas of the basin causing significant damages in Cambodia and Vietnam, and the flood in 2001 caused significant damages in Northeast Thailand. 3 The project is funded by the Dutch government. The six other basins are the Rhine (Western-Europe), Sacramento (USA), Syr Darya (Central Asia), Volta (Ghana), Walawe (Sri Lanka) and Zayandeh (Iran). Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

3

2. NATURAL RESOURCES 2.1. Climate The MRB is located in the Southeast Asia where the climate is governed by monsoons-steady winds that blow alternately from the northeast and the southwest, each for about half of the year. The southwest monsoon begins in May and continues until late September. The northeast monsoon is from November to March. April and October are transitional periods with unstable wind speed and direction (Table 1). Table 1: Monsoon season of the MRB (MRC and UNEP, 1997). Cold season Jan Feb Northeast monsoon

Summer season Mar Apr May transition

Rainy season Jun

Jul

Aug

Cold season Sep

Oct

Nov Dec Northeast monsoon

Southwest monsoon

The regional rainfall varies significantly from the driest region in the basin (Northeast Thailand) where annual rainfall is mostly between 1,000-1,600 mm, to the wettest regions (Northern and Eastern Highlands) with 2,000-3,000 mm annually (Figure 2). The rainfall station network has gradually expanded from some tens of stations in the 1960’s to almost 600 by year 2000. 292 299 300

During the southwest monsoon (May to October), corresponding to the rainy season, the basin receives most of its annual rainfall, although somewhat shielded by the coastal mountains of Thailand and Cambodia (Figure 3). The high coastal mountains of Vietnam shield the basin during the northeast monsoon, corresponding to the cold and dry season. Cyclonic disturbances may cause widespread rainfall of long duration during July to September, which can cause serious flooding.

241 198

200

165 77

100 8

0

269

15

40

54 14

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 3: Mean rainfall distribution (mm) in the LMB. (Data source: IMC, 1988) 40.0 35.0 30.0

Max

Mean The source of the MRB is located in the 25.0 Min snow-capped Tibetan mountains. 20.0 However, throughout the LMB, the air temperature is remarkably uniformed with 15.0 small variations due to elevation and Jan Feb M ar A pr M ay Jun Jul A ug Sep Oct No v Dec seasonal and maritime influences (IMC, 1988a). Temperatures in the LMB are Figure 4: Monthly temperature (oC) in 1961-1990 at high except during the early part of the Mukdahan in the Northeast Thailand (AIT, 1994) northeast monsoon (NovemberDecember) when the winds from Central Asia bring somewhat cooler air. Then, temperature gradually rises up until February when, under the influence of light southerly winds, the weather becomes very hot. This high temperature last until southwest monsoon commences in May (Figure 4).

Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

4

Figure 2: Rainfall stations and mean annual isohyets in the LMB in 1985 (IMC, 1988a) Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

5

2.2. Topography The general topography of the LMB is shown in Figure 5. There are seven principle landform sections in the MRB (Hirsch and Cheong, 1996, MRC and UNEP, 1997, MRC, 2003a). The key characteristics of MRB landforms are compared in Table 2. 1/ Upper Mekong (UM): The section of the MRB in China (or the Lancang river) is steep with variable elevation from 6,740 m to 317 m, and the river is contained in narrow gorges for most of its length. Tributary watersheds include high mountainous terrain leading down from the Tibetan plateau, and lower but nevertheless steep topography in lower Yunnan province. 2/ Northern Highlands (NH): The Northern Highlands cover the section of the MRB in Burma, northern Thailand and northern Lao PDR. Relief is sharp with slopes exceeding more than 30% and forest covered, although this has been reduced considerably in the last 20 years. Several of the peaks rise to over 2,000 metres, and typical crest heights are more than 600 metres above valley floors. Steep slopes combined with vegetation clearance lead to high rates of erosion. 3/ Eastern Highlands (EH): The Eastern Highlands with a width of 50-300 km form the eastern and southern Lao PDR, the western part of Vietnam’s Central Highlands, and small parts of eastern Cambodia. They constitute the western slopes of the Truong Son range (Annamite Chain), which show complex and often sharp relief features but slope less abruptly than the eastern side of the range in Vietnam. Table 2: Key characteristics of MRB landforms (UNEP and MRC, 1997) Landforms

Rainfall (mm/year)

Vegetation

Lancang River Basin

Variable: 600-2,700

Northern Highlands

Wet: 2,0002,800

Korat and Sakon Plateau

Relatively dry: 1,0001,600

Eastern Highlands Lowlands

Wet: 2,0003,200 Variable:1,1 00-2,400

Upland savannah, rain forest Arable land

Southern Uplands

Relatively wet: 1,600

Dense forest

Mountain brush, meadow, pine forest, mixed evergreen & broad-leaved, arable land Grassland, hill evergreen and mountain forest Scrub, grassland, arable land

Pop. Density (pers/km2) Low to moderate: 7-145

Chief economic activity Agriculture (frequently shifting)

Low: 8-15

Agriculture (frequently shifting) Agriculture (irrigated and rainfed)

Moderate: 80-160 Low: 6-33 Moderate to dense: 10570 Very low: less than 8

Agriculture (shifting) Agriculture (rice cultivation) Undeveloped, some shifting agriculture

Problems Erosion, forest degradation, natural disasters Erosion, forest degradation Limited water resources, floods and drought, salinization, rather low fertility Erosion, soil degradation , forest degradation Flooding, acid-sulfate soils, salinity intrusion, drought Vulnerable environment natural reserve

4/ Korat Plateau (KP): Most of the plateau lies within northeastern Thailand and has been extensively cleared for agriculture and is now relatively densely populated. More than half of the Plateau is drained by the Chi and Mun river system and the remainder is drained by several smaller and shorter tributaries flowing directly into the Mekong. It is the driest area of the MRB, with low rainfall and poor moisture retention capacity for most of the soils. Parts of the plateau are underlain by saline evaporates which are mined for salt. During the dry season, saline water seeps through the topsoil resulting in soil salinity,

Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

6

which may be exacerbated by irrigation. Relief is mainly rolling, and rivers are generally incised several metres below the surface of the mainly sandstone plateau.

UM

NH

KP

EH

LL SU

MD

Figure 5: Elevation map of the LMB (MRC, 2000). Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

7

5/ Lowlands (LL): The Mekong lowlands cover a large part of the northern of Cambodia and extend into small portions of southern Lao PDR and eastern Thailand. The river itself is broken between highlands and lowlands by the Khone Falls, a substantial navigational obstacle, but also a site of extensive wetland areas with significant aquatic biodiversity. Another feature of immense resource and environmental importance in section is the Great Lake (or Tonle Sap Lake), the largest inland water body in Southeast Asia, with an area ranging from 3000 km2 in the dry season to over 13,000 km2 in the flood season4. During the flood season Mekong River water drains into the Great Lake through the Tonle Sap River, and as the water level in the Mekong goes down water drains out from the Lake into the Mekong River and the Bassac River, one of the two main branches of the Mekong River, into the Delta. The reversal of the flow of the Tonle Sap River is a unique hydrological phenomena that ensures a higher dry season flow for the delta than if it only received water from the Mekong River. 6/ Southern Uplands (SU): A small section of uplands in southern Cambodia forms the narrow south western rim of the MRB. It is drained by rivers flowing northward into the Great Lake and by the Prek Thnot River into the Bassac River. 7/ Mekong Delta (MD): The Mekong River Delta is a large flat triangle of south-eastern Cambodia and southern Vietnam with an apex at Phnom Penh. Natural levees separate the river from depressions that are subject to flooding during the wet season. Large parts of the delta are flooded in the wet season, forming the Plain of Reeds.

2.3. Land use Forestry and agriculture are the two major land uses in the MRB (Table 3). A picture of the vegetation cover is presented in Figure 6. Table 3: Land cover in the MRB in 1992-1993 based on normalized different vegetation index (NDVI) (data from Kite, 2000). Land cover type Urban Agriculture Semi-desert Shrub land Deciduous forest Evergreen forest Mixed forest Water Tundra Total

%in MRB 0.1 28.6 8.9 17.7 9.1 19.8 13.9 1.5 0.4 100.0

Area(km2) 437 227,518 70,644 140,754 72,717 157,757 110,146 11,643 3,383 795,000

During the last fifty years, forest coverage has declined from over 70% to below 30% due to excessive commercial logging, shifting cultivation, encroachment of reserves for settlements, farming and infrastructure development. Heavy fuel wood 4

Figure 6: Vegetation cover in the MRB synthesized over 10 days from 21 to 31-March-1999 (middle of dry season). Source: EOWorks, Belgium http://www.EOWorks.vito.be

The total extent varies significantly between years.

Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

8

use5 and unclear land ownership has also contributed to this development (MRC and UNEP, 1997). Approximately 175,000 km2, or 30% of the LMB was affected by shifting cultivation (IMC, 1988a). In 1985, forest coverage in the LMB was estimated 27%, lower than all of the national levels because the forest area reduction within the LMB, estimated at 0.7% a year, is much higher than the average of national rates. In Cambodia, the current deforestation rate is estimated at 250,000 ha annually, of 1.4% of the total land area. In Laos, the deforestation is estimated at 300,000 ha per year, or 0.9% of the total land area, mainly in the northern part. In the MRB of Thailand, forest area has been declined from 82% in 1961 to only 13% in 1991. The current rate of deforestation in the northeast Thailand is less than 0.3% per year, mainly due to that there are no more commercial timber and primary areas to clear for farming, encroaching and illegal logging is now more risky. In the Mekong River Delta of Vietnam, forest cover of 23% in 1943 was reduced to 9% by 1991. In Yunnan province, the forest cover of over 70% in 1950 has been reduced to 47% at present. Only in Myanmar, the deforestation rate is low. Agriculture is a dominant economic sector in the MRB. About 75% of the population in the basin are dependent on agriculture and fisheries. Rice production, mainly based on rainfed cultivation, is the most important crop in the MRB. Rice cropping areas in the LMB, about 11.7 million ha in 1999-2000, accounts for over half of the total rice cropping areas of the four riparian countries (Table 4). Table 4. Paddy cultivation in riparian countries in 1985 and 2000 Annual production of paddy

Cambodia

LaoPDR

Thailand

Vietnam

LMB

National(1985) Area(.000ha)

1,345

663

9,833

5,703

17,544

1.3

2.3

2.1

2.8

2.3

1,873

690

10,048

7,655

20,366

Yield(t/ha) 2.0 3.1 2.3 LMB(1985) Area(.000ha) 1,345a 663a 4,200b Yield(t/ha) 1.3 2.3 1.7 LMB(1999-2000) Area(.000ha) 2,079 718 4,813 Yield(t/ha) 1.81 2.92 1.97 Note: a assume most of rice area is within the LMB b c Source: Maclean et al., 2002, except IMC, 1988a and GSO, 1996

4.3

2.1

2,251c 3.1

8,459 2.1

Yield(t/ha) National(2000) Area(.000ha)

3,987 4.08

In Lao PDR, the agricultural sector is very important, providing 40% of foreign currency income, about 52% of the GDP and 80-90% of employment. Food supply in the country is dependent on wet rice cultivation, hence it is vulnerable to drought. An estimated 800,000 ha are cultivated annually (IMC, 1988a), of which 700,000 ha is for rice. A similar area is used for grazing land, and about 300,000 ha are for shifting cultivation. During last few decades, rice production had increased by improvement in yield even though total areas remained stable. The agricultural development goals continued to address food security, as well as to provide income-generating activities by growing a second crop. Therefore there was a gradual increase in irrigated areas from 1990-96, concentrating mainly on rehabilitation of 5

In Cambodia 95 percent of its energy requirements for cooking and boiling water comes from fuel wood, in Lao PDR the figure is 80 percent of cooking energy requirements are provided by fuel wood. A substantial proportion of wood felled is for fuel, and this is true for Thailand and Viet Nam as well (MRC and UNEP, 1997). Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

9

existing schemes. From 1996-2000, such rehabilitation continued, and the construction of new pumped irrigation schemes were implemented. The irrigated areas expanded rapidly from 1996-2000, with about seven-fold increase in both dry and wet seasons. Therefore other non-rice crops such as maize, vegetables, tobacco, and fruits can be grown in the dry season. Agriculture in Thailand accounts for approximately one-fifth of the total GDP, 60% of the export value and 70% of total employment. The northeast part of Thailand, which lies mainly in the MRB, has about 8.5 million ha of arable land, about half of the total arable land of the country. However, the irrigation area only amounts to 0.5 million ha. Rice subsistence farming has a long history in the MRB of Thailand. Substantial development in the region commenced after Thailand became a borrowing member of the World Bank in 1949 (WUP, 2001a). By 1987, the irrigation area is 198,700 ha by small scale irrigation for 2,200 projects, 156,000 ha of medium scale irrigation for 243 medium scale projects and 160,000 ha of pumped irrigation for 589 pumped schemes. No large scale irrigation areas have been developed in recent times, largely because of the lack of large storage sites that are economically justified and environmentally acceptable. The irrigation development led to an increasing in agricultural land approximately 3-4% each year between 1987 and 1994. In Cambodia, the harvested areas averaged 1.5 million hectares until 1986, and then increased to an average of 1.9 million hectares in 1992-1993 and 2,1 million in 1999. The area of the lowland rice receiving supplementary irrigation was estimated at about 300,000 ha, or about 20%. Of the 140,000 ha of dry season rice, about 20,000 ha was estimated to be irrigated, and the remaining 120,000 ha was grown by recession cropping. The Vietnamese Mekong River Delta is an agriculturally and ecologically rich area with a potential agricultural area of 3.9 million ha and extensive mangrove forests near the coast. On the other hand, the Vietnamese Central Highlands in the MRB is relatively undeveloped agriculturally. The Delta contains about 2.4 million hectares of rice cultivation, or about 50% of the paddy production in Viet Nam (NEDECO, 1993), but only a fraction of this area can be irrigated in the dry season due to salinity intrusion. Water management is extremely complex in a dense canal network, and agricultural development depends on four key factors: (i) availability of irrigation and drainage; (ii) salinity of water; (iii) flood depth and duration; and (iv) acidity leached out from acid-sulphate soils. After 1975, agricultural development initially focused on self-sufficiency in rice production, and high-yielding varieties of rice were promoted. Agricultural areas increased by approximately 20% between 1976-1990, however, total production doubled. In 1985, Vietnam was still net rice import country, but in 1989, it exported 1.4 million tons of rice, and the exported amount was highest in 1999 with 4.6 million tons, mainly from the Mekong River Delta (Maclean et al., 2002). Areas of non-rice crops, mainly soybean, mung bean, groundnut, maize, sesame and kenaf, were largely static with an average of about 3% of the agricultural land.

2.4. Surface water resources The Mekong River has abundant of surface water resources with a total of approximately 475,000 million m3 per year. The catchment of Lao PDR contributes 35% of this total, Yunnan, Thailand and Cambodia catchments contribute each between 15-20%, the Vietnamese catchment contributes just over 10% and the lowest contribution is from Myanmar, with only 2% (Table 5). Highest runoff is observed in the Lao PDR at the west of the Anamite Mountains (Figure 7) where annual rainfall is as high as 2,000 to over 3,200 mm per year (Figure 2).

Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

10

Table 5: Distribution of rainfall and runoff in MRB catchment belong to each country

Yunnan Myanmar Lao PDR Thailand Cambodia Vietnam

2

Catchment area (km )

147,000

24,000

65,000

777,000

22

3

25

23

19

8

100

1,561

*

2,400

1,400

1,600

1,500

1,750 c

Average flow (m3/s) from area

2,414

300

5,270

2,560

2,860

1,660

15,060

Average runoff (mil m3) Dry season runoff (mil m3)

76,128

9,461

166,195

80,732

90,193

52,350

474,932

19,032

1,419

24,929

12,110

13,529

7,852

71,240

Catchment area as % of total MRB b

202,000 184,000

MRB Total

155,000

a

Average rainfall (mm/year)

a

Catchment inside MRB

Description

Average runoff as % of total MRB 16 2 35 17 19 11 Source: ENSIC, 1999 a Note: (MRB) excluding the part inside Qinghai province and Tibet Autonomous Region of China b Value by country estimated by different authors (see ENSIC, 1999) c The annual total by IMC (1988a) in Fig. 7 is only 1,672 mm/year.

100

The hydrological regime of the Mekong River is primarily dependent on the climatic conditions of the alternating wet and dry season. The high water period lasts from August to October in the upper part in the basin and September to November in the lower part (Figure 8). The flood season starts June-July and ends in November-December with a peak in September (Figure 8), and accounts for 85-90% of the total annual runoff. During the dry season, the monthly flow accounts only 1-2% of annual flow (MRC and UNEP, 1997). Mean annual flow at different locations from upstream to downstream (Table 6) shows a great increment from Nong Khai (4,490 m3/s) to Kratie (13,700 m3/s). Table 6: Mean monthly flow at stations from upstream to downstream Station Chiang Saen Sop Kok

Mean Station (m3/s) 2.270 Mukdahan 2.940 Khong Chiam

Mean (m3/s) 7.420 9.220

Chiang Khan

4.210 Pakse

10.100

Pa Mong

4.280 Kratie

13.700

Vientiane

4.500 Phnom Penh Tan Chau & 4.490 Chau Doc

14.600

Nong Khai Nakhon Phanom

6.980

14.200

Figure 8: Stage hydrographs of the LMB in 1950 (Hori, 2000)

Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

11

Figure 7: Mean annual runoff isolines, mean monthly distribution of runoff, flood problem areas and hydrometric stations in 1985 (IMC, 1988a). Note: Hydrological year in the MRB starts from April. Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

12

In general, water throughout the MRB is of good quality with localized exceptions. Basinwide, oxygen levels are good. Total Suspended Solids (TSS) show a relatively small number of very high TSS measurements during high flow events and lower values during the rest of the year, a common phenomenon in rivers. In the dry season, salinity is high in the Korat plateau in Thailand and the Vietnamese Delta is affected by saltwater intrusion. Localized perturbations are principally caused by natural processes (soil erosion and siltation, evaporate salt leaching, saltwater intrusion, acid leaching) and human activities including agro-chemical use (Truong and Tin, 1997), and industrial and domestic waste discharge.

2.5. Ground water resources Groundwater resources in the MRB have not been adequate assessed, but it is thought that there is a large untapped potential (MRC and UNEP, 1997). At present, groundwater resources in the basin are mainly used for domestic consumption and industry such as food processing, and some used for irrigation. In the Northeast Thailand, aquifers of recent alluvium from 1 to 10 m deep flank the main Mekong river. Rainwater seepage recharges groundwater resources, with an estimated 5-6% reaching these aquifers. The quantity of groundwater extraction, mainly for domestic use and some for irrigation, has not been large enough to cause a continuous aquifer depletion. Much of the aquifers are saline and not suitable for domestic or irrigation purposes. In Cambodia, groundwater resources are considered insufficient for large scale irrigation, but besides domestic consumption, groundwater is used for small scale irrigation of vegetable and fruit trees. It is reported that more than 6,000 wells has been drilled since 1980, and in the Cambodian delta, the extraction rate has increased dramatically from 120,000 m3/day in 1997 to 290,000 m3/day in 2000. In Vietnam, there is abundant groundwater in the Mekong River Delta. The potential capacity of groundwater is estimated at 60 million m3/day and the actual capacity is over 420,000 m3/day. As in other countries, groundwater is mainly used for domestic and industrial consumption, estimated at 244,000 m3/day in 1997, of which about 150,000 m3/day was in the urban areas (MRC and UNEP, 1997). In the Vietnamese highlands of the MRB, a severe drop in groundwater level has been observed in many areas due to over-exploitation for high income crops, mainly coffee. In general, groundwater quality is good, but it is affected by various pollution sources and disturbances. The pollution could be from salinity intrusion, acid, salt and other leaching from soils, nitrates and nitrites, from fertilizers and pit latrines, and pesticides. In Northeast Thailand, groundwater salinity is often high due to the presence of rock salt. In the Vietnamese Mekong Delta, groundwater is affected by salt water intrusion from the sea and acid sulphate leaching from the acid sulphate soils, and infiltration of agricultural runoff. The lowering of groundwater level due to over-pumping or changes in topography is common due to major pumping from the alluvial aquifers.

2.6. Soils Twenty-nine soil types, falling into two general categories, have been identified in the MRB (MRC and UNEP, 1997): (i) upland soils: podsols, red and black soils, lateritic and mountain soils; and (ii) lowland soils: located in the Korat plateau in Northeast Thailand, the Mekong plain and delta. These soils are coastal complex, delta, flood plain and groundwater complex soils. An overview of soils in the MRB is shown in Table 7. According to the soil classification used for the water balance study in 1988 (IMC, 1988b), 40% of the soils in the LMB are alluvial deposited. Soil quality is decreasing in localized areas, particularly in the Korat plateau in Thailand (saline soils), Lancang valleys (lateritic soils), and Vietnamese Central Highlands (eroded basalt soils). Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

13

Table 7: Soils of the MRB (UNEP and MRC, 1997) Yunnan Myanmar Lao PDR Thailand Cambodia Vietnam

18 different soil types, including laterite, yellow laterite, crimson creamy, yellow and brown soils, brown coniferous forest soils Generally lateritic soils have low fertility, orgaic content of less than 2%, with high soil erosion Red lateritic soils and granites (mountains); clay loams to sandy loams (slopes); sandy clay loams to clay alluvia (valley) Northern Highlands: heavily leached and acidic soils with low water retention capacity & low fertility. Eastern Highlands: similar soils to Northern Highlands, except to the Bolovens plateau, wich has deep, well structured, less acidic soil with good water retention and drainage capacity. River plains: acidic shallow, recent alluvial deposits, low fertility Northeastern Thailand heavy accumulation of salt in typically fine, sandy loam that retains little moisture Three major soil types: alluvial, basaltic and sandstone The Mekong tributaries serve to build up the fertile, alluvial soils in the lowland Mekong Delta: Acid sulfate (1.6 million ha.), saline (996,900 ha.), and alluvium (1.2 million ha.), ancient alluvium (115,890 ha.) upland soils (31,000 ha.) Central Highlands: basaltic soils (about 1 million ha.)

2.7. Environmental issues The current status of the physical environment in the MRB ranges from good to very good, although accurate and detailed information on different environmental indicators is limited. However, degradation of factors such as surface water, both quantity and quality, groundwater quality, soil properties, is expected in the future. A summary of the environmental issues related to development activities is given in Table 8. In this list, the agricultural intensification and expansion is important because of the extent and impacts at national as well as transboundary scale, but information on it is still poor. UNEP and MRC (1997) also assessed that the surface water quantity and quality are the most vulnerable factors that is affected by most human activities in the MRB. Table 8: Issues regarding development activities (UNEP and MRC, 1997) No.

Issue

TempoInforSpatial ral mation scale scale base

1

Development of water way, road and air transport and of electricity transmission links may negatively impact resource use and sustainability

F

T

F

2

Shifting cultivation, increase logging, and encroachment are degrading watersheds and affecting resource use and sustainability

F

T

C&F

3

Development activities, impacting fish habitats, and increased demand and consumption are resulting in decreased fish populations

P

T

C&F

4

Urban and industrial wastes (solid, liquid, gaseous, and hazardous) threaten resource use and sustainability

F

N&T

F

5

Irrigation development in saline soils and improper rock-salt exploitation on the Korat Plateau and Vientiane Plain adversely impacts resource use & sustainability

F

T

F

6

Agricultural intensification and expansion increases the use of agro-chemical, degrading water quality

P

N&T

C&F

7

Conversion of acid-sulfate soil to agricultural use affect resource use and sustainability

P

L

C&F

8

Intensive salinity control in the Mekong Delta causes adverse impact resource use and sustainability

F

L

C&F

F

L

F

9 Irrigated agricultural intensification and expansion decrease water availability Notes:

Information base - P: poor, F: fair, G: good Spatial scale - L: localized, N: national, T: transboundry Temporal scale - C: current, F: future

Climate Change Impact and Adaptation on Water, Food, and Environment in Mekong River Basin, Southeast Asia

14

The highlands in Lao PDR, Cambodia and Vietnam are host to many rare and endangered species including the recently discovered Vu Quang Ox and the Giant Muntjak, a type of deer. The wetland areas in the MRB are important habitats for migratory birds and resident wildlife. The river systems themselves are habitat to over 1,000 species of fish and include many rare species such as the Mekong River dolphin and the giant catfish. In Lao PDR, 18 National Biodiversity Conservation Areas covering 25,015 km2 have been declared by the Government. In Thailand, national parks cover 39,983 km2 of Thailand (8% of the total area) but few of these conservation areas are located in the Northeast of Thailand. In Cambodia, the conservation area is about 19% of the whole country. The Vietnamese Mekong Delta contains about 50,000 ha of conservation areas (1.3% of the total area) while the Vietnamese Central Highlands has about 446,700 ha of conservation areas (8% of the total area). However, resource competition between conservation areas and agricultural expansion is repeated throughout the LMB.

2.8. Socio-economic characteristics Population The MRB has a population of approximately 65 million in the 1995-2000, of whom about 55 million are in the LMB (Table 9). The area and population at the end of the 21st century in the six riparian countries in the MRB are shown in Table 9 (Hori, 2000). The proportion of the MRB in the total area and population of each country reflects the position of this basin within the country. Although, in China the MRB account only 2% of land area and 1% of population, it forms a significant part of Yunnan province (19% and 13%). The basin is most important for Cambodia and Lao PDR of which most of the country drains into the basin. In Thailand and Vietnam, the MRB area is less than a quarter of the country area, but a significant proportion of the population lives in basin indicating its importance for these countries. The great majority of the MRB inhabitants are farmers and fishers, relying quite directly on the natural resource base, and as illustrated in Figure 9, the pressure on agricultural land is high in the entire basin. Table 9: Land areas and populations (1995) in the six riparian countries Land area (103 km2)

Total populatio n (106)

Land area within MRB Area 3 (10 km2)

Population within MRB

China (Yunnan)

395.0

39.0

147.0

% of country or province 37

Myanmar

676.6

46.5

24.0

4

3

0.9

2