This session pays tribute to Hannes Flühler - a scientific leader and mentor, and the 2004 EGU John Dalton Medalist. The session celebrates Hannes’s many contributions to soil physics and vadose zone hydrology. His creativity and optimism in addressing flow and transport processes in unsaturated porous media were always guided by the cautionary principle of “digging deeper”. Meaning that we must revert to physical fundamentals and question incomplete explanations to observations.
His approach is even more relevant today where artificial intelligence and computational capacity transform data analysis and modelling, enabling consideration of increasingly complex scenarios across hydrology, land-surface science, plant physiology and agronomy. Meanwhile, societal expectations concerning soil health, ecosystem resilience and food security create new demand for rigorous soil physics offering new opportunities, but also a risk that sophisticated computations may obscure fundamental gaps in understanding. An illustrative example of these contemporary challenges is taken from work of Hannes Flühler (Flühler et al., 1976). Field measurements of unsaturated hydraulic conductivity differ markedly from laboratory measurements and model predictions, which naturally raise questions about the transferability of hydraulic descriptions from laboratory to field conditions. The example motivates us to take a deeper look at the physical basis and applicability of our description of soil processes.
In the spirit of Hannes Flühler’s approach, we invite contributions that dig deeper into fundamental questions in soil physics and hydrology. We encourage early career scientists and students to submit their work to this session. We welcome experimental, theoretical and computational studies that investigate discrepancies between observations and predictions, examine how soil structure and moisture history affect flow and transport, and test the transferability of hydraulic descriptions across scales and changing environmental conditions.

Flühler, H., Germann, P., Richard, F., & Leuenberger, J. (1976). Bestimmung von hydraulischen Parametern für die Wasserhaushaltsuntersuchungen im natürlich gelagerten Boden. Ein Vergleich von Feld‐und Laboratoriumsmethoden. Zeitschrift für Pflanzenernährung und Bodenkunde, 139(3), 329-342.