Tracking Fluvial Inundations and Groundwater Recharge Areas in the Upper Mekong Delta by Combining Sentinel-1, SWOT, and In-Situ Data

Annual monsoon inundations are essential ecosystem services in the Cambodian Mekong Delta. These floods support agricultural cycles, fish production, ecosystem regulation and potentially groundwater recharge. However, recent development of hydropower and irrigation infrastructures, land use and climate change have influenced hydrological processes including surface water and groundwater exchanges. Satellite imagery like Sentinel-1 has been widely used in previous studies to map inundation extent due to its temporal availability in all weather conditions. Nevertheless, Sentinel-1 is limited by unwanted interference from vegetation, terrain, and anthropogenic features. Data from the Surface Water and Ocean Topography (SWOT) mission launched in December 2022, equipped with Ka-band Radar Interferometer (KaRIn), provides a complementary perspective by providing two-dimensional water surface elevations and extent from which water volumes can be estimated. To help better characterise surface water flows that may percolate into the deep aquifer, this study presents a methodology for tracking river dynamics and floodplains inundation  over the Mekong Delta in Cambodia, using a combination of SWOT and Sentinel-1. The datasets obtained from the two satellites  are compared with in-situ water level and discharge data and evaluate their effectiveness for tracking the river dynamics, inundation extent, and flow quantification. This validation is performed over the Tonle Sap River, a tributary of the Mekong River, and provides insights into the functionality of the ecosystem within the study region. This study also explores potential estimation of the possible contribution of the groundwater recharge areas to the groundwater budget.