Introduction

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Critical issues

The Mekong is one of the world's largest river basins (IMC, 1988) with an area just under 800,000 km2. It is shared by six countries: China (Yunnan Province), Union of Myanmar, Lao PDR, Kingdom of Thailand, Kingdom of Cambodia and Vietnam (Fig. 8.1). The basin is the home to over 65 million inhabitants (MRC and UNEP, 1997). The Lower Mekong River Basin (LMB) covers 77% of the Mekong River Basin (MRB) and is regarded as the most important part of the Mekong Basin, both environmentally and economically. The population in LMB is largely rural and most people are employed in agricultural or related activities, with rice as the major crop. Agricultural production is one of the five key areas of natural resources and development in the region (Nilsson and Segnestam, 2001). The other areas are hydropower generation, fisheries, forest resource management and the use of biological resources for conservation, tourism, trade and local livelihoods.

Although the Mekong riparian countries enjoy abundant water resources, availability varies widely across regions and seasons due to the monsoon rainfall pattern. Competition for scarce water resources is particularly evident during the dry season. There are several emerging issues regarding water usage in the MRB: (i) irrigation development in North-east Thailand has resulted in a lack of water during the dry season and restricts the amount of dry season cropping possibilities; (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 floods; (iv) hydropower development, built or proposed, with distribution of

© CAB International 2004. Climate Change in Contrasting River Basins

Fig. 8.1. Location of Mekong River Basin.

benefits across countries and sectors not thoroughly evaluated; and finally, (v) growing populations and increasing economic development is starting to affect water availability negatively by degrading the water quality (MRC, 2001).

With a high population density per rice land (4.7 persons/ha in the LMB) and severe floods during the last few years, in this study we focus on two issues in the MRB: food production and flood under climate change (CC).

Physical characteristics

The MRB is located in South-east 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

Fig. 8.2. Mean rainfall distribution (mm) in the LMB.

Fig. 8.3. Monthly temperature in 1961-1990 at Mukdahan in North-east Thailand.

late September. The northeast monsoon is from November to March. April and October are transitional periods with unstable wind speed and direction.

The regional rainfall varies significantly from the driest region in the basin (North-east Thailand), where annual rainfall is mostly between 1000 and 1600 mm, to the wettest regions (northern and eastern Highlands) with 2000-3000 mm annually. During the southwest monsoon (May to October), corresponding to the rainy season, the basin receives most of its annual rainfall, although it is somewhat shielded by the coastal mountains of Thailand and Cambodia (Fig. 8.2). Cyclonic disturbances may cause widespread rainfall of long duration duringJuly to September, which can cause serious flooding.

Throughout the LMB, the air temperature is remarkably uniform, with small variations due to elevation and seasonal and maritime influences (IMC, 1988). Temperatures in the LMB are high, except during the early part of the northeast monsoon (November-December) 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 lasts until the south-west monsoon commences in May (Fig. 8.3).

The MRB comprises of seven principal landform sections with different characteristics. The Mekong River has abundant surface water resources, with a total of approximately 475,000 million m3/year (Table 8.1). The catchment of Lao PDR contributes 35% of this total; Yunnan, Thailand and Cambodia catchments each

Fig. 8.2. Mean rainfall distribution (mm) in the LMB.

Fig. 8.3. Monthly temperature in 1961-1990 at Mukdahan in North-east Thailand.

Table 8.1. Distribution of rainfall and runoff in MRB catchment by country. Source: ENSIC (1999).

Catchment inside MRB

MRBa

Table 8.1. Distribution of rainfall and runoff in MRB catchment by country. Source: ENSIC (1999).

Catchment inside MRB

MRBa

Description

Yunnan

Myanmar

Lao PDR

Thailand

Cambodia

Vietnam

Total

Catchment area

147,000

24,000

202,000

184,000

155,000

65,000

777,000

(km2)

Catchment area as

22

3

25

23

19

8

100

% of total MRBa

Average rainfall

1,561

-

2,400

1,400

1,600

1,500

1,750'

(mm/year)b

Average flow

2,414

300

5,270

2,560

2,860

1,660

15,060

(m3/s) from area

Average runoff

76,128

9,461

166,195

80,732

90,193

52,350

474,932

(million m3)

Dry season runoff

19,032

1,419

24,929

12,110

13,529

7,852

71,240

(million m3)

Average runoff as

16

2

35

17

19

11

100

% of total MRB

c a MRB excluding the part inside Qinghai province and the Tibet Autonomous Region of China.

b Value by country estimated by different authors (see ENSIC, 1999).

The annual total by IMC (1988) is only 1672 mm/year.

contribute between 15% and 20%; the Vietnamese catchment contributes just over 10% and the lowest contribution is from Myanmar, with only 2%. The highest runoff is observed in the Lao PDR west of the Anamite Mountains.

Socio-economic and institutional characteristics

The most notable economic feature of countries in the LMB is the difference in average levels of GNP between the wealthiest and poorest countries (Ringler, 2001). A key issue in Mekong Basin development and management is the cross-sectoral implications of interventions (Hirsch and Cheong, 1996). The population of the MRB is mainly agrarian-based, with rice as the major crop. The proportion of arable land under irrigation in the LMB is fairly low: about 20% in Laos, Thailand and Cambodia and 50% in the Vietnamese Mekong Delta, suggesting good opportunities for expansion. Vietnam on the whole retains only some 20% of its original moist forests compared to 43% for Thailand, 55% for Lao PDR and 71% for Cambodia. The LMB is considered to support one of the richest river faunas in the world. Fish production in the LMB is predominantly from capture fisheries (about 90%) and total production is estimated to range from 624,301 to 887,473 tonnes. However, including small-scale fisheries, it was estimated that actual catches may exceed 1 million tonnes per year (Hirsch and Cheong, 1996). Fish is the primary source of animal protein in the LMB and comprises from 40 to 80% of the total animal protein intake (IMC, 1988, 1992).

As early as 1947, preliminary studies and reports recognized the need for an international organization to coordinate activities and promote cooperation among the nations of the MRB. The Committee for Coordination of Investigations of the Lower Mekong Basin was formed in 1957 with four member countries: Lao PDR, Thailand, Cambodia and Vietnam, with a general, but limited, mandate to 'promote, coordinate, supervise and control the planning and investigations of water resource development projects' (Radosevich and Olson, 1999). In the decades that followed, the Mekong Committee focused on both short-term tributary projects and longer-term mainstream projects, but the development of the tributaries was regarded as the most important short-term issue. In 1978 the Mekong Committee was replaced by the Interim Committee for Coordination of Investigations of the Lower Mekong Basin with three members: Lao PDR, Thailand and Vietnam (MRC Secretariat, 1989), and in 1991 Cambodia requested re-admission and reactivation of the Mekong Committee. Then, the Agreement on the Cooperation for the Sustainable Development of the MRB (Mekong Agreement) was signed in 1995. The Mekong River Commission (MRC) replaced the Interim Mekong Committee with a new structure and with an agenda to address a host of environmental, social and economic challenges, and is expected to take on a strong role in coordinating planning, development and management of the MRB (MRC, 1995).

Projection of population and food demand

In this study, we applied two different population growth rates for scenarios A2 and B2 to project the population in 2025 and 2085, the middle years of two periods 2010-2039 and 2070-2099, with the assumption that population in A2 will be higher than in B2 (Table 8.2). Based on population in 2000, population in A2 in 2025 and 2085 are 93.0 and 186.2 million, respectively, while in B2 these numbers are 86.5 and 137.8 million in 2025 and 2085. Food demand is assumed to be increased in proportion with population growth. With the assumption of unchanged individual food demand of 300 kg per capita/year (ENSIC, 1999), overall food demand will be increased by 1.3-1.4 times in 2025 and 2.1-2.9 times in 2085 (Table 8.2).

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