Future changes in Mekong River hydrology: impact of climate change and reservoir operation on discharge

Abstract

The transboundary Mekong River is facing two ongoing changes that are expected to significantly impact its hydrology and the characteristics of its exceptional flood pulse. The rapid economic development of the riparian countries has led to massive plans for hydropower construction, and projected climate change is expected to alter the monsoon patterns and increase temperature in the basin. The aim of this study is to assess the cumulative impact of these factors on the hydrology of the Mekong within next 20–30 yr. We downscaled the output of five general circulation models (GCMs) that were found to perform well in the Mekong region. For the simulation of reservoir operation, we used an optimisation approach to estimate the operation of multiple reservoirs, including both existing and planned hydropower reservoirs. For the hydrological assessment, we used a distributed hydrological model, VMod, with a grid resolution of 5 km × 5 km. In terms of climate change's impact on hydrology, we found a high variation in the discharge results depending on which of the GCMs is used as input. The simulated change in discharge at Kratie (Cambodia) between the baseline (1982–1992) and projected time period (2032–2042) ranges from −11% to +15% for the wet season and −10% to +13% for the dry season. Our analysis also shows that the changes in discharge due to planned reservoir operations are clearly larger than those simulated due to climate change: 25–160% higher dry season flows and 5–24% lower flood peaks in Kratie. The projected cumulative impacts follow rather closely the reservoir operation impacts, with an envelope around them induced by the different GCMs. Our results thus indicate that within the coming 20–30 yr, the operation of planned hydropower reservoirs is likely to have a larger impact on the Mekong hydrograph than the impacts of climate change, particularly during the dry season. On the other hand, climate change will increase the uncertainty of the estimated reservoir operation impacts: our results indicate that even the direction of the flow-related changes induced by climate change is partly unclear. Consequently, both dam planners and dam operators should pay closer attention to the cumulative impacts of climate change and reservoir operation on aquatic ecosystems, including the multibillion-dollar Mekong fisheries

Modelling future changes of habitat and fauna in the Tonle Sap wetland of the Mekong

“…Spatial analysis was carried out with a digital elevation model (DEM) derived from bathymetry and topography surveys in the open water and throughout most of the floodplain, and complemented with data from the shuttle radar topography mission (SRTM) in the upland regions (Kummu & Sarkkula 2008) surrogate of historical habitats and land use. Projected water levels under future scenario of hydropower development and climate were derived from two basin-wide hydrological models (Lauri et al 2012;Piman et al 2013).…”

“…Arias, unpublished data 2013). The application of these two scenarios represents a near future scenario of development and an extreme development scenario; however, the methodology can also be applied to any of the scenarios presented in Piman et al (2013) or Lauri et al (2012). We also present additional results illustrating the analysis for a climate change scenario (A1b emissions scenario simulated with the ECHAM 5 global circulation model).…”

“…Projected changes in the seasonality of the Mekong hydrology as a result of climate change are expected to be less extreme than for hydropower; there is a high degree of uncertainty in the predictions depending on the global circulation model used (Lauri et al 2012). While we opted not to focus on climate change predictions for this paper, the methodology presented is fully applicable to such scenarios.…”

“…Knowledge of ecological properties and interactions in the Tonle Sap is limited (Lamberts 2006;Kummu et al 2006), yet this wetland is facing many ecological changes as a result of imminent disruptions to its hydrology (Kummu & Sarkkula 2008). Hydrological changes in the Mekong basin caused by hydropower and climate change will result in a modified flood pulse, mainly through reductions in seasonal water level variability homogenizing the system (dams) and increasing interannual uncertainty (climate change) (Lauri et al 2012). These hydrological changes may in turn result in permanent alteration of habitats (Arias et al 2012).…”

Spatial and temporal variation of benthic macroinvertebrates in the Nam Gnom Basin receiving discharged waters from the Nam Theun 2 Reservoir (Lao PDR)

“…In Southeast Asia, the Mekong River basin is recognized for its high hydropower potential (Lauri et al, 2012;Ziv et al, 2012). An estimation of 200 hydropower projects are located in the "Greater Mekong Sub-region", which includes Thailand, Cambodia, Myanmar, Vietnam, Yunan Province (China) and Lao PDR (Souksavath & Nakayama, 2013).…”