From Varied Irrigation Regimes to Flood-Induced Crop Failure: An 8-Year Simulation of Hydrodynamics and Scenario-Based Assessment of Short-Chain Perfluoralkyl and Polyfluoralkyl Substance Leaching Under Sequential Storms Daniel and Elias in Thessaly,

Sequential extreme hydrological events driven by climate change pose severe risks to both crop survival and groundwater quality in flood-prone agricultural regions. The current study investigated the long-term soil hydrodynamics and potential perfluoralkyl and polyfluoralkyl substance (PFAS) leaching in a mountain tea (Sideritis raeseri) plantation in Thessaly plain, Greece, before, during and after the consecutive extreme storms Daniel and Elias (in September 2023). An 8-year simulation was performed, covering the years 2018–2025, including an initial calibration/validation phase (2018) followed by the 2019–2025 simulation of hydrodynamics and potential short-chain PFAS leaching, under two hypothetical solute transport scenarios. Model HYDRUS-1D was calibrated and validated using field data (precipitation, irrigation, evaporation, transpiration and biomass) from the 2018 growing season under four irrigation treatments (100%, 75%, 50% and 0% of ETc, where ETc is crop evapotranspiration) to secure reliable soil hydraulic properties and was subsequently extended to simulate soil water dynamics until 2025, when crop failure was observed. To quantify environmental risks, two hypothetical solute transport scenarios with different initial depths of contamination (0–20cm and 0–100 cm) and an initial short-chain PFAS soil pore water concentration of 0.1 ppb (equal to upper EU limit) were executed exclusively for the 2019–2025 period to simulate the potential leaching of the contaminants through the soil. The simulation successfully captured the agronomic reality, showing that prolonged waterlogging conditions persisted, suggesting a severe risk of root anoxia, potentially leading to the subsequent crop failure in 2025. Furthermore, solute transport modeling captured the leaching process and predicted that under typical Mediterranean hydrological conditions, short-chain PFAS had already potentially leached beyond the root zone prior to the extreme events. However, the sequential floods acted as an acute hydraulic flush, evacuating the residual chemicals towards deeper soil layers. Moreover, the 0–100 cm contaminated profile represents the most critical hazard to the underlying aquifer, delivering a higher load and elevated risks for the groundwater table than the shallow (0–20 cm) contamination profile.