A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Water Engineering and Management

Thesis (M. Eng.) - Asian Institute of Technology, 2023

The Lancang Mekong River Basin is not only a vital water resource system supporting the livelihoods of millions of people, but it is also one of the most diverse ecosystems in the world, supporting a wide range of flora and fauna. The hydrological regime of the river is expected to undergo significant alterations due to climate change, leading to potential water scarcity and flood hazards in the region. In this context, this study aimed investigating the potential impact of climate change on the streamflow and groundwater recharge in Lancang Mekong River Basin and flood hazard potential in Cambodian Mekong floodplain. The study was carried out employing three CMIP6 climate models namely ACCESS-CM2, BCC-CSM2-MR and ECEarth3 selected from performance evaluation of eight GCMs under SSP2-4.5 and SSP5-8.5 scenarios. Soil and Water Assessment Tool (SWAT) hydrological model was developed to assess the impact of climate change on hydrology in the basin in terms of annual and monthly variability of river discharge, changes in high and low flows and groundwater recharge. The results indicated that the hydrological regime of the river is expected to undergo significant changes in the future, with an overall increase in average annual streamflow and groundwater recharge in the basin exhibiting spatial variability in magnitude of change. MIKE FLOOD model was developed for Cambodian Mekong floodplain to investigate the potential impact of climate change on flood hazard in the Cambodian Mekong floodplain. The results signaled an increased streamflow will exacerbate flood hazard in the floodplain in the coming future due to climate change. Moreover, the study also explored the influence of flooding on groundwater resource in the Cambodian Mekong floodplain using GMS-MODFLOW groundwater model. The Mekong River during flooding season is one of the major sources of recharge to the floodplain groundwater aquifer and receives water from the groundwater during dry season. This contribution to floodplain groundwater aquifer recharge during the flooding season is projected to increase in the near future.