High Resolution Modeling of River-Floodplain-Reservoir Inundation Dynamics in the Mekong River Basin

Numerous studies have examined the changes in streamflow in the Mekong River Basin (MRB) using observations and hydrological modeling; however, there is a lack of integrated modeling studies that explicitly simulate the natural and human-induced changes in flood dynamics over the entire basin. Here we simulate the river-floodplain-reservoir inundation dynamics over the MRB for 1979-2016 period using a newly integrated, high-resolution (similar to 5 km) river hydrodynamics-reservoir operation model. The framework is based on the river-floodplain hydrodynamic model CaMa-Flood in which a new reservoir operation scheme is incorporated by including 86 existing MRB dams. The simulated flood extent is downscaled to a higher resolution (similar to 90 m) to investigate fine-scale inundation dynamics, and results are validated with ground- and satellite-based observations. It is found that the historical variations in surface water storage have been governed primarily by climate variability; the impacts of dams on river-floodplain hydrodynamics were marginal until 2009. However, results indicate that the dam impacts increased noticeably in 2010 when the basin-wide storage capacity doubled due to the construction of new mega dams. Further, results suggest that the future flood dynamics in the MRB would be considerably different than in the past even without climate change and additional dams. However, it is also found that the impacts of dams can largely vary depending on reservoir operation strategies. This study is expected to provide the basis for high-resolution river-floodplain-reservoir modeling for a holistic assessment of the impacts of dams and climate change on the floodpulse-dependent hydro-ecological systems in the MRB and other global regions.