Water scarcity has become one of the major issues to environmentalist, researchers and mostly to society and its people. The rapid increasing population, socio-economic development and climate change has exacerbated the water scarcity situation. The uncertainty in the future societal and climate conditions will increase the scarcity risk. Therefore, this study aims to explore the water scarcity responses to future socio-economic development called Share Socio-economics Pathways (SSPs) and climate change named Representative Concentration Pathways (RCPs) for the three period of 2030s, 2060s and 2090s in the transboundary 3S (Sekong, Sesan and Srepok) Basin. The three SSPs i.e., SSP1, SSP2 and SSP3 and two RCPs i.e., RCP4.5 and RCP8.5 were selected for projection of future water scarcity risk. In which, the SSP1 was combined with RCP4.5 and two remain SSPs are compatible with RCP8.5. The results show that the basin experienced stress condition and it will increase till 2090s under SSP2 and SSP3 scenarios. The basin would expose to the worse situation of scarcity in the dry years. Furthermore, the projected spatial water scarcity distribution map reveals that the extreme scarcity mainly occurred in the upstream of Sesan and Sre Pok sub-basin located in Vietnam. Among the three water stress mitigation options, water transportation is the effective option for reducing the medium and severe scarcity status. The results of this study will contribute the enlighten the water scarcity situation and will be assets to policy makers and stakeholders for effective decision making in development of water resource management of complex transboundary river basin.