In the paper the evaporation front is considered the interface that separates the wet part of a porous medium from its dry surroundings, and its exact definition in time and space is given. Subsequently, the law of the front's motion is derived. The general problem governing completely the front's motion is formulated and, for a special case, solved numerically. It is shown that the solution makes it possible to locate the rate of vaporization in time and space.

Salinity and sodicity can cause irreversible degradation to soil, threatening agricultural production and food security. To date, very little is known about the degree to which soil degradation can be reversible. We introduce a model for describing this partial reversibility (hysteresis) and lay out the experimental procedures necessary for characterizing the soil in this regard. We must shift our focus from degradation measurements to reversal measurements so that we can maintain healthy soils.

This is the last paper submitted by Peter Germann before he died in December 2020. Peter reviews the development of capillary flow theory since the work of Briggs (1897) and Richards (1931), who raised capillary flow to a soil hydrological dogma. Attempts to correct the dogma led to concepts of non-equilibrium flow, macropore flow, and preferential flow during infiltration. Viscous film flow is proposed as an alternative approach to capillarity-driven flow during unsaturated infiltration.

The way soils capture infiltrating water affects crops and natural vegetation and groundwater recharge. This retention of soil water is described by a mathematical function that covers all water contents from very dry to water saturated. We combined two existing lines of research to improve the behaviour of a popular function for very dry and very wet conditions. Our new function could handle a wider range of conditions than earlier curves. We provide fits to a wide range of soils.

Increasing fire frequency and severity now poses a threat to most of the world's wildlands and forested ecosystems and their benefits. The HMV (Heat–Moisture–Vapor) model is a tool to manage fuels to help mitigate the consequences of fire and promote soil and vegetation recovery after fire. The model's performance is surprisingly good, but it also provides insights into the existence of previously unobserved feedbacks and other physical processes that occur during fire.

The amount of water stored in the soil is critical for the productivity of plants. Plant productivity is either limited by the available water or by the available energy. In this study, we infer this transition point by comparing local observations of water stored in the soil with satellite observations of vegetation productivity. We show that the transition point is not constant with soil depth, indicating that plants use water from deeper layers when the soil gets drier.

More than 300 years after its first appearance, Perrault's De l'origine des fontaines provokes intriguing stimuli and suggestions. We discuss its epistemological relevance through the lens of the repeatability of the experiments, of the didactic aspects which arise for modern teaching of hydrology, and of the author's attitude in facing the complexity of the hydrological processes. The analysis shows that the birth of modern hydrology and the scientific revolution were closely entwined.

We find that the stable isotopic compositions of mobile and matrix bound soil water are continuously different over 8 months. Long-term data further show that these isotopic differences result from the refilling of small soil pores by isotopically depleted rains during low soil moisture conditions. Thus, subsurface water is not well mixed, but flow velocities and storage in soils are highly variable; this has important implications for ecohydrological studies and soil hydrological modeling.

This study explores the relationship between drip water and rainfall in a SW Australian karst, where both intra- and interannual hydrological variations are strongly controlled by seasonal variations in recharge. The hydrological behavior of cave drips is examined at daily resolution with respect to mean discharge and the flow variation. We demonstrate that the analysis of the time series produced by cave drip loggers generates useful hydrogeological information that can be applied generally.

We sampled the isotopic composition in the top 20 cm at four different sites in the Scottish Highlands at 5 cm intervals over 1 year. The relationship between the soil water isotopic fractionation and evapotranspiration showed a hysteresis pattern due to a lag response to onset and offset of the evaporative losses. The isotope data revealed that vegetation had a significant influence on the soil evaporation with evaporation being double from soils beneath Scots pine compared to heather.

This paper investigates soil water migration processes in the Loess Plateau using isotopes. The soil water migration is dominated by piston-type flow, but rarely preferential flow. Soil water from the soil lay (20–40 cm) contributed to 6–12% of plant xylem water, while soil water at the depth of 40–60 cm is the largest component (range from 60 to 66 %), soil water below 60 cm depth contributed 8–14 % to plant xylem water, and only 5–8 % is derived from precipitation.

In this study dimensionally consistent governing equations of continuity and motion for transient soil water flow and water flux in fractional time and in fractional multiple space dimensions in anisotropic media are developed. By the introduction of the Brooks–Corey constitutive relationships, an explicit form of the equations is obtained. The developed governing equations, in their fractional time but integer space forms, show behavior consistent with the previous experimental observations.

This theoretical paper describes the energy fluxes and dissipation along the flow paths involved in root water uptake, an approach that is rarely taken. We show that this provides useful additional insights for understanding the biotic and abiotic impediments to root water uptake. This approach shall be applied to explore efficient water uptake strategies and help locate the limiting processes in the complex soil–plant–atmosphere system.

Vertisols are cracking clayey, arable soils that often overlay groundwater reservoirs. The soil cracks enable flow that bypasses soil blocks, which results in both relatively fresh recharge of the underlying groundwater and contamination with reactive contaminants. These special phenomena, as well as unique mechanism of salinization after cultivation and relative resilience to contamination by nitrate typical to groundwater under vertisols, are reviewed in this study.

This study investigates the effects of river restoration on groundwater–surface water interactions in a losing urban stream. Investigations were performed using Distributed Temperature Sensing (DTS). The results indicate that the highest surface water downwelling occurred at the tip of a gravel island newly installed during river restoration, leading to the conclusion that in this specific setting, river restoration was effective in locally enhancing groundwater–surface water interactions.

Soil moisture was observed along a strong semi-arid climatic gradient in a Mediterranean karst area. Soil moisture data and soil hydraulic modelling with Hydrus-1D revealed a strong dependency of percolation fluxes with rainfall amounts and intensity during heavy rainfall events. Spatial and temporal extrapolation of the model illustrated the high variability of seasonal percolation amounts among single years and showed strong correlations between soil depth and potential groundwater recharge.

The characteristics of the macropore network determine the potential for fast transport of solutes through soil. Such characteristics computed from 3-dimensional X-ray tomography images were combined with measured solute breakthrough curves and near-saturated hydraulic conductivities. At a given flow rate, smaller macroporosities, poorer local connectivity of the macropore network and smaller near-saturated hydraulic conductivities resulted in a greater degree of preferential transport.