Climate change uncertainty in environmental flows for the Mekong River

A MIKE SHE model of the Mekong, calibrated and validated for 12 gauging stations, is used to simulate climate change scenarios associated with a 2 degrees C increase in global mean temperature projected by seven general circulation models (GCMs). Impacts of each scenario on the river ecosystem and, hence, uncertainty associated with different GCMs are assessed through an environmental flow method based on the range of variability approach. Ecologically relevant hydrological indicators are evaluated for the baseline and each scenario. Baseline-to-scenario change is assessed against thresholds that define likely risk of ecological impact. They are aggregated into single scores for high and low flows. The results demonstrate considerable inter-GCM differences in risk of change. Uncertainty is larger for low flows, with some GCMs projecting high and medium risk at the majority of locations, and others suggesting widespread no or low risk. Inter-GCM differences occur along the main Mekong, as well as within major tributaries.