Coupled modelling approach to assess effects of climate change on a coastal groundwater system

The effect of future climate change on groundwater resources was assessed using a modelling approach for a coastal area in Vietnam. In this study, the distributed hydrological model (PANTA RHEI) was coupled with the finite element subsurface flow system model (FEFLOW) to predict the future variation of groundwater resources. The assessment of the seasonal variability of climate conditions on the variation of groundwater recharge and groundwater levels (GWLs) in different aquifers was analysed for the historical (1986–2005), present (2013–2014), and future (2046–2065) period. The domain groundwater model covers approximately 50 km². The groundwater model was calibrated and validated using hourly measured groundwater levels at 11 monitoring wells within the study area. The necessary information on geological formations, hydrogeological parameters, and groundwater abstraction rate were implemented in the groundwater model set up. One representative concentration pathway (RCP8.5) is considered for projecting future conditions of groundwater resources.The results of this study showed that future rainfall was projected to decrease both in wet and dry seasons. Groundwater recharge was projected to decrease significantly in the dry season (10.9%) compared to the wet season (2.6%). As a result, groundwater levels were also projected to decline in future. Stronger declining trends were detected for deeper groundwater, especially in the dry season with declines of 6.7–20.2 m. The model results also showed that the GWLs are largely influenced by the natural recharge through precipitation in the study area. These findings may help decision–makers and stakeholders for devising sustainable groundwater management strategies in coastal area.