Land use change uncertainty impacts on streamflow and sediment projections in areas undergoing rapid development: A case study in the Mekong Basin

Abstract

Quantitative understanding of potential changes in streamflow and sediment load is complicated by uncertainty related to land use change projections, which is characterized by a high uncertainty in terms of demand (quantity) and location of changes (spatial distribution). We simulate the Sesan, Srepok, and Sekong Rivers (3S), the most important tributaries of the lower Mekong River, with the Soil and Water Assessment Tool (SWAT) to investigate the implications of conversion of forest to agricultural lands. Multiple land use transitions in the 3S basin are projected using the Land Change Modeler. The uncertainty in land use projection was addressed using an ensemble forecasting approach for 2060, combining (a) three land demand scenarios, (b) two transition potential modeling approaches (i.e., approach to create maps of the likelihood for areas to transition from one land use type to another), and (c) retaining or not protected areas. Land demand leads to the greatest uncertainty in land use change projections. Transition potential modeling approaches do not make much difference in the total change, but can result in spatial variations of change. Retaining protected areas can contribute significantly to uncertainty in land use change projections. Decrease in annual streamflow of the 3S basin varied from 3% to 21%, and changes in annual sediment outflux from the basin ranged from −8% to 249% for simulated scenarios. Land use demand uncertainty results in the highest streamflow and sediment load changes and can thus have major consequences for water and sediment management strategies in areas undergoing rapid development.

Using the Freshwater Health Index to Assess Hydropower Development Scenarios in the Sesan, Srepok and Sekong River Basin

“…While simplified, these scenarios also give insight into how the governance system may shape future hydrological changes, and how these may affect the resident human population. A next step will be to incorporate more models such as for land-use change [29,83] and climate change [83,84] and collect further information on stakeholder perceptions and the factors influencing decision-making, as well as to continue to improve the collection and accessibility of relevant datasets in the 3S River basin. This would allow both a better assessment of current conditions in the 3S and calculation of additional indicators for future scenarios, providing decision-makers with more detail upon which to contemplate.…”

“…These dams would also have negative impacts on fish migration and diversity [17,27]. Moreover, the basin is experiencing extensive deforestation [28] from illegal activity and industrial agriculture, which is likely to alter the provisioning services of water catchment and sediment transport, the latter potentially compensating for sediment trapped by dams [29].…”

A Review of SWAT Studies in Southeast Asia: Applications, Challenges and Future Directions

“…Some of the earliest applications of SWAT in the SEA were for hydrologic analyses of the Mekong River basin [14,39,40]. Analyses of parts or all of the Mekong system with SWAT have continued to the present [41][42][43][44][45] along with increasing numbers of studies that have been performed for specific watersheds located in various SEA countries [46][47][48][49][50][51][52][53]. These SWAT studies have been performed for a wide range of water resource issues, watershed size, and climatic conditions, but there have been no analyses to date of the overall implications of these studies for the SEA region.…”

A Modeling Approach to Diagnose the Impacts of Global Changes on Discharge and Suspended Sediment Concentration within the Red River Basin

“…SWAT has been applied in Asian basin and performed well in various simulations [35,[58][59][60], and also in tropical areas [61][62][63][64][65][66]. In South East Asia, SWAT was commonly applied to Mekong river basin [35,60,67] or some local small-scale basins [42,58,61,65,[68][69][70][71]. This paper applied the SWAT model in a large-scale basin in the tropical South East Asia.…”

“…Although SWAT has been applied to many Asian basins, and also to subtropical or/and tropical areas, most of them were at a scale of 77 to 105,000 km 2 [31][32][33][34][35]. The Red River is a typical Asian river system, combining different land uses, affected by human activities such as intensive dam implementations and agriculture [36,37].…”