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Cai Y.,National Biodiversity Center | Vidthayanon C.,Mekong River Commission Secretariat
Raffles Bulletin of Zoology

A new species of stygobitic freshwater prawn, Macrobrachium spelaeus from Tham Phra Wang Daeng, Pitsanulok Province, in northern Thailand, is described and illustrated in detail. Morphological comparisons with allied epigean species M. dienbienphuense and known stygobitic congener M. poeti are given. The new species is characterised by its reduced eyes, smooth and slender second pereiopods, hairy chelae and short carpus of second pereiopods, and elongated telson. © National University of Singapore. Source

Piman T.,University of Canterbury | Lennaerts T.,Mekong River Commission Secretariat | Southalack P.,Mekong River Commission Secretariat
Hydrological Processes

The Mekong is one of the world's great rivers. It has the greatest mean annual flow in the world for a river basin of comparable size. The flow regime, with very distinct wet and dry seasons, supports a rich biodiversity and the world's largest freshwater fishery. Given that at the present time the hydrological regime of the Mekong remains in its natural state, the accelerating pace of water resources development will induce hydrological change. The natural productivity of the system is therefore potentially jeopardized. This paper reports the findings of simulation studies of the potential hydrological impacts of water resource development scenarios over future planning horizons. In the Definite Future scenario (next 5years), the seasonal redistribution of water by on-going hydropower development will increase the dry season flow by 40-60% in the upper portion of the basin and by 20-30% in the Mekong Delta. The Foreseeable Future scenario (next 20years) and Long-Term Future scenario (next 50years) will result in relatively small changes to the flow regime as further increases in dry season reservoir releases will be offset by planned increases in irrigation and other consumptive water demands. All scenarios were predicted to reduce the average wet season flows by 4-14%, flow reversal to the Tonle Sap Lake by 7-16%, flooded areas by 5-8% and salinity intrusion areas in the Viet Nam Delta by 15-17%. Predicted changes in Definite Future scenario will be irreversible, necessitating improved coordination between the LMB countries and cooperation with China in order to manage the risks and maximize the regional benefits. The scenario assessments highlighted the areas where research is necessary to mitigate and manage impacts in order to ensure the reasonable and equitable use of the Mekong basin's water resources. © 2013 John Wiley & Sons, Ltd. Source

Shrestha B.,Asian Institute of Technology | Babel M.S.,Asian Institute of Technology | Maskey S.,UNESCO-IHE Institute for Water Education | Van Griensven A.,UNESCO-IHE Institute for Water Education | And 5 more authors.
Hydrology and Earth System Sciences

This paper evaluates the impact of climate change on sediment yield in the Nam Ou basin located in northern Laos. Future climate (temperature and precipitation) from four general circulation models (GCMs) that are found to perform well in the Mekong region and a regional circulation model (PRECIS) are downscaled using a delta change approach. The Soil and Water Assessment Tool (SWAT) is used to assess future changes in sediment flux attributable to climate change. Results indicate up to 3.0°C shift in seasonal temperature and 27% (decrease) to 41% (increase) in seasonal precipitation. The largest increase in temperature is observed in the dry season while the largest change in precipitation is observed in the wet season. In general, temperature shows increasing trends but changes in precipitation are not unidirectional and vary depending on the greenhouse gas emission scenarios (GHGES), climate models, prediction period and season. The simulation results show that the changes in annual stream discharges are likely to range from a 17% decrease to 66% increase in the future, which will lead to predicted changes in annual sediment yield ranging from a 27% decrease to about 160% increase. Changes in intra-annual (monthly) discharge as well as sediment yield are even greater (-62 to 105% in discharge and -88 to 243% in sediment yield). A higher discharge and sediment flux are expected during the wet seasons, although the highest relative changes are observed during the dry months. The results indicate high uncertainties in the direction and magnitude of changes of discharge as well as sediment yields due to climate change. As the projected climate change impact on sediment varies remarkably between the different climate models, the uncertainty should be taken into account in both sediment management and climate change adaptation. © Author(s) 2013. CC Attribution 3.0 License. Source

Piman T.,University of Canterbury | Cochrane T.A.,University of Canterbury | Arias M.E.,University of Canterbury | Green A.,Mekong River Commission Secretariat | Dat N.D.,Mekong River Commission Secretariat
Journal of Water Resources Planning and Management

The Mekong River supports unique biodiversity and provides food security for over 60 million people in the Indo-Burma region, yet potential changes to natural flow patterns from hydropower development are a major risk to the well-being of this system. Of particular concern is the ongoing and future development of 42 dams in the transboundary Srepok, Sesan and Sekong (3S) basin, which contributes up to 20% of the Mekong's annual flows and provides critical ecosystem services to the downstream Tonle Sap Lake and the Mekong Delta. To assess the magnitude of potential changes, daily flows were simulated over 20 years using the HEC ResSim and SWAT models for a range of dam operations and development scenarios. A 63% increase in dry season flows and a 22% decrease in wet season flows at the outlet of the 3S basin could result from the potential development of new dams in the main 3S rivers under an operation scheme to maximize electricity production.Water-level changes in the Mekong River from this scenario are comparable with changes induced by the current development of Chinese dams in the Upper Mekong Basin and are significantly higher than potential flow changes from the proposed 11 mainstream dams in the Lower Mekong Basin. Dams on the upper sub-tributaries of the 3S basin have very little effect on seasonal flow regimes because most of those projects are run-of-the-river dams and have small reservoir storages. The effects on hourly flow changes resulting from intra-daily reservoir operations, sediment movement, water quality, and ecology require further study. Strategic site selection and coordinated reservoir operations among countries are necessary to achieve an acceptable level of development in the basin and to mitigate negative effects in seasonal flow patterns, which sustain downstream ecosystem productivity and livelihoods. © 2013 American Society of Civil Engineers. Source

Adamson P.,Mekong River Commission Secretariat | Bird J.,Mekong River Commission Secretariat
International Journal of Water Resources Development

The notion of drought as a hydro-meteorological hazard in tropical monsoon regions is not perhaps one that fits naturally with conventional perceptions. The term 'monsoon' is commonly regarded as synonymous with torrential rainfall, moisture surplus, floods and climatic predictability. The paper seeks to dispel such perceptions in a review of recent historical events within the Lower Mekong Basin. A weak monsoon results in deficient flows and water levels that can have severe impacts upon agricultural production across the Cambodian flood plain and the delta in Viet Nam, where natural and controlled inundation is the basis of padi rice production. Lower flows also cause an increase in saline intrusion in the delta, which further reduces agricultural output. The impacts of an early end to monsoon conditions on agriculture in Thailand and Lao PDR are also revealed, which serves to emphasize the potential negative consequences of climate change which not only is expected to result in the increased inter-annual variability of regional rainfall, but also there could be impacts upon its seasonal pattern and timing. In concluding, the paper refers to building drought management capacity in the region through a climate change and adaptation initiative, including forecasting, impact assessment, and the development of management, preparedness and mitigation policies. © 2010 Taylor & Francis. Source

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