Process-based 3D groundwater flow model to simulate current and future stream intermittence in headwaters

While the role of climate conditions in controlling streamflow intermittence is well recognised, the assessment and modelling of the role of groundwater remains a challenge. In this study, we use process-based 3D groundwater flow models to simulate stream intermittency in groundwater-fed headwaters. Streamflow measurements and stream network maps are considered together to constrain the effective hydraulic properties of the aquifers. The modelling framework has been applied and validated in pilot catchments with unconfined crystalline aquifers (France) with contrasting geomorphological settings. We present the calibration framework, the analysis of uncertainties and discuss the underlying mechanisms governing the different dynamics of streamflow intermittency. The models are then used to predict streamflow intermittence under future climate scenarios. Intuitively, with decreasing recharge rates, systems with lower storage capacities lead to higher water table fluctuations, increasing the proportion of intermittent streams and reducing future perennial flows. However, the pilot sites reveal nuanced feedback mechanisms among future climate variations, groundwater recharge dynamics, and stream intermittence, where the geomorphic characteristics of the landscapes are key to regulating these feedbacks.