Modeling groundwater dynamics in a low-lying sedimentary island driven by recharge variability, climate change, and water demand

Climate warming is reshaping seasonal recharge variability with growing implications for groundwater-dependent regions. Although seasonal recharge variability is increasingly recognized as a key control on groundwater dynamics, uncertainties remain regarding how hydraulic head and baseflow respond to these seasonal shifts, particularly across aquifers with varying hydrogeologic properties. We developed and calibrated a high-resolution transient groundwater flow model using MODFLOW 6 for Prince Edward Island (PEI), the only Canadian province almost entirely reliant on groundwater. We performed a series of model simulations to quantify the sensitivity of hydraulic heads and baseflow across the island under varying seasonal recharge, future climate change, and increasing water demand. The results indicate that spring recharge governs the magnitude of summer baseflow across PEI. Seasonal recharge stress tests indicate that spring and summer recharge deficits decrease groundwater and baseflow anomalies. Combined spring–summer deficits produce more than a two-fold increase in summer baseflow reductions compared with single-season deficits. Spring surpluses with summer deficits provide limited buffering. Under the high-emission climate projection scenario for far-century, hydraulic head anomalies increase across all seasons (+3% to + 19%), while baseflow anomalies increase in winter (+66% to + 113%) and fall (+20% to + 38%), but decline in spring (−26% to − 35%). Under the projected pumping scenario, seasonal anomalies increase moderately, while the seasonal pattern remains consistent. Regional anomaly differences demonstrate that drought sensitivity is controlled by hydrogeologic properties, with high (low) transmissivity aquifers responding rapidly (slowly) to seasonal recharge variations. These insights provide policy implications for strengthening drought resilience and managing groundwater sustainably.