Climate change impacts on flood hazards and surface-subsurface water interactions in the Lancang Mekong River Basin

Abstract

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 availability alteration and flood hazards in the region. In this context, this study investigates the basin response to these shifts, particularly focusing on Cambodian Mekong floodplain of Lancang Mekong River Basin. By scrutinizing the surface–subsurface interactions, the research aims to comprehensively understand the dynamics of water flow in the region in the face of climate change. Multi-modelling approach with development of Soil and Water Assessment Tool (SWAT) hydrological model, MIKE FLOOD hydrodynamic model and GMS-MODFLOW groundwater model were used for projecting the flood hazard and quantifying the surface–subsurface interactions in Cambodian Mekong floodplain.

The results indicated that the hydrological regime of the basin is expected to undergo significant changes in the future, with an overall increase in average annual streamflow by 14.58 % to 17.27 % and groundwater recharge by 7.53 % to 12.99 % under SSP 2–4.5 and SSP 5–8.5 scenarios respectively while exhibiting spatial variability in magnitude of change. The increased streamflow will exacerbate flood hazard in the floodplain in the coming future due to climate change. Likewise, 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.