Stefanie Kiemle war bis 31.12.2025 Mitarbeiterin am Lehrstuhl für Hydromechanik und Hydrosystemmodellierung (LH2). Sie ist Mitglied der SimTech Graduate School (GS SimTech) und wird am Donnerstag, den 12. März 2026 ihre Doktorarbeit mit dem Titel "Modelling and analysis of evaporation-driven transport processes across the porous medium–free flow interface: from stable water isotopologue fractionation to salt-induced dynamics" verteidigen.
Datum: Donnerstag, den 12. März 2026
Uhrzeit: 14:00 Uhr
Ort: MML, U. 1.003, Pfaffenwaldring 61, 70569 Stuttgart
Abstract
Evaporation in porous media regulates liquid water availability, solute redistribution, and energy exchange at the soil–atmosphere interface, processes that control hydrological fluxes, agricultural sustainability, and land–atmosphere interactions. As climate change intensifies evaporative demand, understanding how evaporation modifies soil moisture and solute distributions becomes increasingly important for predicting environmental hazards such as soil degradation and groundwater contamination.
This thesis addresses two main objectives: (i) to investigate evaporation-driven fractionation processes of stable water isotopologues as tracers of soil drying, and (ii) to analyse the stability of salt-induced dynamics in evaporating porous media.
Evaporation-driven fractionation processes of stable water isotopologues. We developed and validated a numerical model capable of simulating flow and transport of stable water isotopologues in drying soils. The model successfully reproduced isotopic fractionation at the evaporation front and was evaluated against analytical solutions, state-of-the-art simulations, and high-frequency experimental data. Our results demonstrate that residual water saturation and its numerical representation strongly affect simulated isotopic fractionation, especially during stage-II evaporation.
Furthermore, by explicitly coupling porous media with the overlying free flow, we showed that kinetic isotopic fractionation can be resolved without relying solely on empirically defined fractionation factors. These findings establish isotopologues as robust natural tracers of evaporation dynamics and highlight the importance of accurate representations of the soil–atmosphere interface.
Stability analysis of salt-induced dynamics in evaporating porous media. The stability of the system fundamentally determines which processes occur in evaporating porous media—whether salt precipitates or density-driven instabilities develop. The objective of this work is to identify the conditions under which the system transitions between stable and unstable regimes. To this end, we employ numerical multiphase, multicomponent transport models that describe the distribution of dissolved salts during evaporation. These are complemented by a linear stability analysis and high-resolution 3D MRI experiments, which enable direct observation of the evolution of salt concentrations. By combining numerical modelling with linear stability analysis, we investigate the influence of soil-water saturation on system stability. Our results show that lower saturation levels lead to an earlier onset of density-driven instabilities, making the system more unstable. Comparison of the numerical model with the MRI experiments demonstrates that the model can qualitatively reproduce the spatial development of salt distribution and finger formation. However, temporal deviations from the experiments occur, primarily due to simplified boundary conditions and the limited scale of the experimental setup. These aspects require further investigation to more accurately capture system stability in later phases.
Overall, this work advances the understanding of evaporation-driven isotopic fractionation and salt transport in porous media, providing new insights into how soil systems respond to drying. The results are directly relevant for improving evaporation modelling, interpreting isotopic signatures, and assessing the risks of salinization and groundwater contamination under increasing evaporative demand.
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