Eco-hydrological modeling of a tropical catchment exposed to anthropogenic pressure and climate impact

To date, the water quality management of the Thi Vai Estuary in South Vietnam has solely focused on the industrial zones located at the shoreline of the estuary. Although the catchment is a prominent pollution source for the Thi Vai Estuary, it was ignored by the local authorities up to now. Within the BMBF research project EWATEC-COAST a coupled model system was developed. It consists of an eco-hydrological catchment model and a hydrodynamic water quality model for the tidal main river. The eco-hydrological model, which was calibrated with data collected in the project, is in the focus of this contribution. Water and substance balances of the catchment were simulated for an extended historical time period with the calibrated eco-hydrological model PANTA RHEI-WQ using available meteorological long-term series. It was demonstrated that today the catchment is a primary source of pollution for the Thi Vai Estuary, delivering higher substance loads than the adjacent industrial zones. It was also shown, that the upper part of the Thi Vai is the current pollution hot spot. Approximately 55 % of the substance load from the catchment and approx. 35 % of the substance load from the industrial zones are entering the Thi Vai in that area. Furthermore the impact of climate change (2046 to 2065) on the water quantity and quality was quantified and was compared to a combined scenario, which accounts for a progressive development of the anthropogenic pollution in addition to climate change. It was demonstrated, that, under the given boundary conditions, the anthropogenic impact on water quantity and quality is stronger than the impact of climate change on its own. It was also shown, that the combined scenario of climate change and anthropogenic development can lead to an amplification of negative effects.