The Mekong region is undergoing rapid transitions, socially, economically, and environmentally. Economies are stabilizing after the political turbulence of the last several decades, and development pressures as well as ambitions are vast. Water is related to these social, economic, and environmental changes in many ways and in a very profound manner. This article summarizes the approach and major conclusions of the research project title “Integrated Water Resources Management (IWRM) on the Mekong River.” The concept of IWRM is elaborated in the setting of these major transitions, and the roles of academic research and education are highlighted.

The sediment loads of many of the world's major rivers have changed significantly in recent years due to land-use change, reservoir construction, and other human impacts on their drainage basins. For many rivers, the loads have decreased, whereas for others, they have increased. Such changes can have important implications for both the natural functioning of the system as well as for human exploitation of the river system. This paper considers the evidence for recent changes in the sediment load of the Mekong River. The available data have a number of limitations in terms of both sampling frequency and the period of coverage, but they have been processed to provide a basis for considering the changes in the sediment load of the river over the period extending from the early 1960s to 2002. Although there is evidence of increasing loads at some measuring stations, the overall trends show little evidence of major changes, and the system provides evidence of buffering through storage. As of 2002, the construction of major dams on the headwaters in China appears to have had little impact on the sediment load, although as further larger dams are commissioned, the sediment load of the Mekong can be expected to decrease.

It has been claimed that Tonle Sap Lake is rapidly filling with sediment as a result of increasing sediment yields from the catchment. Infilling of the lake basin would have serious implications for the magnitude of flooding in central Cambodia and the Mekong Delta region and threaten the lake's unique ecosystem. In this article, we synthesize the results of radiocarbon dating of sediment cores and hydrodynamic modeling results to provide an empirically based assessment of this issue. We find that current sedimentation rates within the lake basin proper are low and have been for several millennia. However, sedimentation at the lake margin and in its floodplain is relatively high, which presents a range of issues for riparian communities.

The wetlands of the lower Mekong River Basin are ecologically and socioeconomically significant, but they are threatened by predicted climatic change. The likely response of wetland ecosystems to altered flooding regimes and surface-water chemistry is unknown in detail and difficult to model. One way of exploring the impact of climate change on wetland ecosystems is to utilize proxy environmental data that reveal patterns of change over geological time. In recent years, the coverage and resolution of proxy climatic data have improved markedly in the region. Recent evidence of the South China Sea transgression into southern and central Cambodia and paleobotanical evidence from the Tonle Sap (“Great Lake”) and elsewhere allow us to explore how periods of higher-than-present sea level and increased monsoon rainfall in the past have impacted the wetland ecology of the lower Mekong River Basin.

Environmental changes and their transboundary influences on the Mekong watercourse system have been an international research focus in recent years, but the opinions and results related to the impacts of upper Mekong River dams are quite different. In this paper, based on the records of water levels from 1960 to 2003 at three mainstream sites in the upper Mekong River, a quantitative examination has been undertaken into characteristics of the mainstream water-level process at multiple timescales and its response to cascade development. The major results are: i) Annual mean, wet period mean, and the mean water levels during the period between March and April (PBMA period) exhibit a significant increasing trend at Jiuzhou and Yunjinghong sites, which are influenced by large-scale factors such as climate change and solar activity. ii) The interdecadal and interannual variations of annual mean, annual maximum, and wet period mean water levels at three sites show similar features during the dam construction period. iii) The interdecadal variations of PBMA period water level show a gradual increase at Gajiu and Yunjinghong sites but a falling trend at Jiuzhou; these trends confirm that there is some regulation on the flow in the dry season caused by the two existing dams. iv) The downstream effects of the present dams on water levels are very limited at the annual mean and wet season mean levels, not apparent at the monthly and yearly timescales, and relatively significant at daily and hourly timescales.

Tonle Sap Lake is a large and complex data-deficient ecosystem in the Mekong River Basin. Highly valuable in biodiversity and natural livelihoods capital, it is susceptible to degradation when the flood pulse that drives its productivity is altered as a result of hydropower and irrigation development on the Mekong River. To date, there are no tools to assess the consequences of such flood pulse alterations, leaving the Tonle Sap underrated in water-resources use and planning. A combined ecological-hydrodynamic model is presented for the production potential of the Tonle Sap ecosystem and its likely response to hydrological changes.

Rapid development in the upper reaches of the Mekong River, in the form of construction of large hydropower dams and reservoirs, large irrigation schemes, and rapid urban development, is putting water resources under stress. Recent studies have concluded that these developments will lead to flow alterations in the Mekong River. These flow alterations would threaten the sensitive ecosystems downstream, particularly Tonle Sap River, Tonle Sap Lake, its floodplain, and its gallery forest and protected areas, by changing the flood-pulse system of the lake. This article estimates the changes in parameters of the Tonle Sap flood pulse due to the aforementioned flow alterations. The impacts on the flooded area and loss of gallery forest and protected areas were analyzed using geographic information system–based methods. Relatively small rises in the dry-season lake water level would permanently inundate disproportionately large areas of floodplain, rendering it inaccessible to floodplain vegetation and eroding the productivity basis of the ecosystem. It is highly important to maintain the natural hydrological pattern of the Mekong River, particularly the dry-season water levels, to preserve Tonle Sap Lake's ecosystem productivity.

The Mekong River Basin is facing rapid changes, including intensive plans for water development. While the different development projects are considered to be important for economic development, the negative impacts that they are likely to cause for ecosystems and livelihoods are estimated to be remarkable. Yet, existing impact assessment processes seem in many cases to be inadequate to capture even the actual magnitude of the impacts at different levels. This article looks at the different impact assessment processes and their challenges in the basin. It is argued that impact assessment in this kind of dynamic and complex setting requires better coordination between assessments at different levels. Basinwide impact assessment would benefit from a more adaptive, multilevel approach that makes better use of assessments from local levels up to the regional level and builds on more participatory and interdisciplinary methods. Successful impact assessment also requires the recognition of the highly political nature of water development and related planning processes.

Large-scale development of irrigation has long been an attractive option of postwar development, and the Mekong region has been no exception. Thailand has developed approximately four million hectares of irrigated land, and its northeastern region (Isaan)—both the driest and poorest part of the country—has been the target of many water projects. However, “full development” of its potential has been constrained by the lack of storage sites and the difficulty of diverting water from the Mekong River. Several ambitious projects have been discussed during the last 50 y, all of which have been aimed at “greening Isaan.” In 2003, the Thai administration launched the idea of a national “water grid” that would triple the area of irrigated land in the country. This paper analyzes the emergence of this megaproject, its governance, and its economic and environmental soundness.

Development in the Mekong Delta of Vietnam has been very dynamic in the recent past, and currently it stands at an interesting crossroads. On one hand, agricultural production has developed successfully, and economic growth has been very rapid, but on the other hand, intensifying agriculture and large-scale water-control structures have challenged the environmental sustainability and social equity. The development plans have included a strong belief in the human mastery over the nature and waters of the Mekong Delta. In many cases, water resources planners have underestimated the complexity and integrated nature of the ecology and livelihoods of the Mekong Delta. This article examines cases where development efforts, while successful in some dimensions, have also contributed to create new risks for, especially, the poorest groups. The current situation calls for a more sustainable future route that would require examination of more adaptive measures in relation to the changing water flows of the Mekong River.

Land-use change processes are commonly understood as simplified cause-effect relationships, which, in turn, support many environment-development policies. This paper uses wide-ranging evidence from a number of global case studies to challenge some of the prevailing “myths” around land-use change in the Mekong Basin and supports the conclusion that the simple explanations found in population growth, poverty, and infrastructure studies rarely provide an adequate understanding of land-use change.

The Mekong River Basin possesses the region's largest potential water source and related resources, which support ongoing economic development and basin community livelihoods. It is currently witnessing a major demographic transition that is creating both opportunities and challenges. An analysis of the complex relationship between demographic changes and impacts on the natural-resource base confirms that resource exploitation is occurring not only to meet growing domestic needs but also for other vested interests. Population, together with other major drivers, such as institutions, markets, and technology, will have a very strong bearing on the way in which the rich resources of the Mekong River Basin are developed and distributed in the present and future. The Mekong River Basin's rich resources, and the benefits derived from them, are unevenly distributed both in time and geographically. Moreover, since the causes and impacts do not respect political boundaries, the Mekong countries need to jointly develop alternative management strategies to meet projected demands within the sustainable capacity of the Mekong River Basin natural-resource base.

Poverty reduction decorates all development agendas, but the complexity of the poverty issue is too often hidden behind simplistic indicators and development goals. Here, a closer look is taken at the concepts of “deprivation” and “vulnerability” as outcomes of poverty. Deprivation leads typically to social exclusion and marginalization; such groups are particularly weak in getting themselves out of poverty by “self-help,” and economic growth does not trickle down to these people. When looking at the connections between poverty reduction and economic growth, special emphasis should be put on the differences between modern and more traditional sectors: development of the modern sector should not marginalize and exclude those dependent on more traditional livelihoods. Two case studies—The Tonle Sap area, Cambodia, and the Mekong Delta, Vietnam—reveal that investment in education, empowerment of small-scale entrepreneurship and other means of microeconomic environment, along with good governance, infrastructure, and income distribution can ensure that economic growth includes the poorer echelons of society.