Coastal freshwater systems face growing threats from climate change and intensified withdrawals, with groundwater and surface water salinization as critical impacts. Variable-density groundwater flow and salt transport (VD-GWT) models are essential tools to understand these processes and thereby predict the impacts of, among others, climate change induced sea-level rise, precipitation changes, and water management strategies. However, computational constraints often force temporal simplifications of input time series such as the recharge. To quantify how temporal resolution affects model predictions of groundwater salinity and salt loads to surface waters, we conduct a sensitivity analysis in which we temporally scale the recharge of an existing, validated VD-GWT model in a low-lying coastal region in the Netherlands. Eight recharge configurations are tested over 50 years, combining four temporal resolutions (yearly, seasonal, monthly, 10-day) with two groundwater recharge averaging methods. Results demonstrate that temporal resolution predominantly affects groundwater-surface water fluxes and salt loads rather than groundwater salinity distributions, with the dense drainage network acting as a temporal filter that limits variability effects to shallow groundwater (1-2 meters depth). Coarser temporal resolutions, particularly yearly, systematically overestimate salt loads and freshwater flushing requirements due to higher average exfiltration fluxes and concentrations and fail to capture critical seasonal patterns. Monthly resolution provides an optimal balance, capturing seasonal patterns essential for irrigation management and freshwater flushing while maintaining reasonable computational demands. These findings underscore that including temporal variability in groundwater recharge is essential to determine accurate water management strategies in similar low-lying coastal regions. Read more here: https://doi.org/10.1016/j.advwatres.2026.105403
