The flood pulse is a key element characterizing the hydrology of the Mekong River and driving the high ecosystem productivity in the Lower Mekong floodplains, both in the Cambodian lowlands and the Mekong Delta in Vietnam. This paper assesses the impacts of climate change, both in terms of changed basin water balance and sea level rise, on the Lower Mekong flood pulse. The impacts were simulated by a three-dimensional hydrodynamic model using the projected changes in sea level and the Mekong mainstream discharge under the influence of climate change as boundary conditions. The model simulations projected that average and maximum water levels and flood duration increase in 2010–2049. The most consistent and notable changes occurred in the average and dry hydrological years. Sea level rise had the greatest effects in the Mekong Delta, whereas the impacts of changed basin water balance were more notable in the upper areas of the Mekong floodplains. The projected impacts were mostly opposite to those resulting from regional water infrastructure development. Higher and longer flooding could cause damage to crops, infrastructure and floodplain vegetation, and decrease the fertile land area. On the other hand, it might boost ecosystem productivity and enhance dry season water availability.

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