 The Mekong River faces two major challenges over the next few decades, the effects of climate change and the construction of new hydropower dams. Climate change is expected to cause significant changes in the river's hydrology, while the construction of new dams could lead to increased uncertainty in the river's water levels. This study assessed the combined effect of these two factors on the river's hydrology, finding that the impact of climate change was greater than that of planned hydropower reservoirs. Additionally, the study showed that the direction of the impact of climate change was uncertain, meaning that the effects of hydropower reservoirs may be more pronounced than previously thought. This article was authored by H. Laurie, H. DeMole, P. J. Ward and others.