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Recent advances in machine learning (ML) techniques show promise for estimating soil hydraulic properties from soil data sets. Pedo‐transfer functions (PTFs) can facilitate the mapping of the complex relationship between soil properties and soil hydraulic properties, for example, lateral hydraulic conductivity—a necessity for estimating lateral subsurface flow in distributed hydrological models. In wflow_sbm model, the horizontal‐to‐vertical saturated hydraulic conductivity ratio fKh0 $\\left({f}_{\\text{Kh0}}\\right)$ is a sensitive parameter, but no established PTF exists. Our objective is to investigate the potential of ML algorithms in estimating PTFs for fKh0 ${f}_{\\text{Kh0}}$ prediction. In this study, publicly available calibrated fKh0 ${f}_{\\text{Kh0}}$ (i.e., optimized) across Great Britain were utilized to train two ML algorithms: Random Forest (RF) and Boosted Regression Trees (BRT), employing SoilGrids data set. Both algorithms effectively predicted fKh0 ${f}_{\\text{Kh0}}$ in 92 of the 115 tested sub‐basins (i.e., 80%), demonstrating a high correlation with the optimized values, with RF slightly outperforming BRT. As a next step, we compared wflow_sbm simulated discharge results using uncalibrated fKh0 ${f}_{\\text{Kh0}}$ (default value) and our predicted values. The predictions notably improved discharge simulations, with a median Kling‐Gupta Efficiency (KGE) increasing from 0.55 to 0.75. Subsequently, we generated two globally distributed fKh0 ${f}_{\\text{Kh0}}$ maps to investigate the transferability of the ML‐based PTFs in the Loire basin, France. ML‐based PTFs improved performance in 75% of sub‐basins, with an average KGE increase of 0.06. Finally, we assessed the uncertainty in fKh0 ${f}_{\\text{Kh0}}$ predictions, confirming the robustness of the ML‐based PTFs. Our study highlights the potential of ML methods for estimating soil hydraulic properties, aiding parameter estimation for distributed hydrological models.

Exact solutions for one‐dimensional steady‐state and transient liquid flow toward a water table in heterogeneous unsaturated soils are critical in predicting saturation profiles in several real‐world applications including interpretation of climate change effects on the subsurface and impacts on slope stability. In this study, vertical heterogeneity in saturated hydraulic conductivity with depth is characterized by an exponential decay function. A steady‐state solution is derived based on Darcy's law and the water table depth, and two transient‐state solutions are obtained from Richards' equation using the Laplace transform and the modified Bessel equation under common upper boundary conditions, that is, flow rate and pressure head, following the initial steady‐state flow condition and a water table at a specified depth. The transient and steady‐state solutions are compared with numerical solutions obtained from a multi‐layered configuration and an analytical solution for homogeneous soils, demonstrating their reliability and efficacy. Various hypothetical heterogeneous soils with differing parameters are employed to assess the flow behaviors, illustrating that vertical heterogeneity impacts the pressure head profiles. More pronounced heterogeneous soils exhibit lower pressure head and effective saturation during flow compared to homogeneous soils, which depend on the air‐entry value and the water table depth, irrespective of the upper boundary conditions. The solution has been employed to predict volumetric water content profiles in the Loess Plateau of China and evaluate the effect of infiltration on the stability of a shallow landslide in Japan based on the infinite slope model and the suction stress concept.

In Mediterranean ecosystems, special attention needs to be paid to forest-water relationships due to water scarcity. In this context, Adaptive Forest Management (AFM) has the objective to establish how forest resources have to be managed with regards to the efficient use of water, which needs maintaining healthy soil properties even after disturbance. The main objective of this investigation was to understand the effect of one of the AFM methods, namely forest thinning, on soil hydraulic properties. At this aim, soil hydraulic characterization was performed on two contiguous Mediterranean oak forest plots, one of them thinned to reduce the forest density from 861 to 414 tree per ha. Three years after the intervention, thinning had not affected soil water permeability of the studied plots. Both ponding and tension infiltration runs yielded not significantly different saturated, [K[s]], and unsaturated, [K][−20], hydraulic conductivity values at the thinned and control plots. Therefore, thinning had no an adverse effect on vertical water fluxes at the soil surface. Mean [K[s]] values estimated with the ponded ring infiltrometer were two orders of magnitude higher than [K][−20] values estimated with the minidisk infiltrometer, revealing probably soil structure with macropores and fractures. The input of hydrophobic organic matter, as a consequence of the addition of plant residues after the thinning treatment, resulted in slight differences in terms of both water drop penetration time, WDPT, and the index of water repellency, [R], between thinned and control plots. Soil water repellency only affected unsaturated soil hydraulic conductivity measurements. Moreover, [K][−20] values showed a negative correlation with both WDPT and [R], whereas [K[s]] values did not, revealing that the soil hydrophobic behavior has no impact on saturated hydraulic conductivity.

Understanding the relationship between root systems, soil macropore networks, and soil hydraulic properties is important to better assess ecosystem health. In this study, treatments were performed in forested wetland soils with different vegetation densities, i.e., large (LWa) and small communities (LWb) of reed (Phragmites australis (Cav.) Trin. ex Steud.). At each plot, three undisturbed PVC cylinders (10 cm in diameter and 50 cm in height) were obtained, and X-ray microtomography (μCT) scanning was used to determine the root and macropore architectures. Results showed that the values of total root length and total root volume at LWa were significantly larger than those at LWb (p < 0.05). Imaged macroporosity, macropore volume, macropore length density, macropore node density, macropore branch density, mean macropore surface area, mean macropore diameter, and mean macropore volume at LWa were significantly larger than those at LWb (p < 0.05), whereas mean macropore length, mean macropore branch length, and mean macropore tortuosity at LWb were larger than those at LWa. Total root length and total root volume were positively correlated with soil saturated hydraulic conductivity. Imaged macroporosity, macropore volume, macropore length density, macropore node density, macropore branch density, mean macropore surface area, mean macropore diameter, and mean macropore volume were positively correlated with soil saturated hydraulic conductivity, whereas mean macropore length, mean macropore branch length, and mean macropore tortuosity were negatively correlated with soil saturated hydraulic conductivity. In conclusion, root systems and soil macropore networks constitute a complex synthesis inside soil environments, and together affect soil hydrological responses.

Superabsorbent polymers (hydrogels) have been studied for their ability to influence soil hydraulic conductivity because they can store and release water due to their swelling properties. However, concerns related to the increased use of synthetic hydrogels necessitates a switch to bio-based hydrogels, which are renewable and more biodegradable in comparison to synthetic hydrogels. In this study, we synthesized a lignin-based hydrogel and amended a silt loam soil with it at concentrations of 0, 0.1, and 0.3% (w/w). A laboratory permeameter, double membrane tension infiltrometer, and evaporation method were used to measure the saturated (Ks), near saturated, and unsaturated hydraulic conductivity (K) of the samples, respectively. Saturated hydraulic conductivity was significantly decreased by the application of hydrogel at 0.1 and 0.3% (w/w) in comparison to the control treatment. The application of 0.3% (w/w) lignin-based hydrogel only significantly decreased hydraulic conductivity at −1 cm soil water pressure head. Hydraulic conductivity in the 0.1 and 0.3% (w/w) treatments increased along the K(θ) curve in the unsaturated zone (−750 cm < h < −10 cm) in comparison to the control treatment, which we hypothesized was due to bound water in the hydrogel being released and creating a wider path for the movement of water. The 0.1 and 0.3% hydrogel treatments also tended to store more water than the control treatment, especially after 24 h of evaporation. The implication of this study is that lignin-based hydrogels could swell and retain water in saturated soils and the bound water could be released to enhance the flow of soil water in unsaturated soil, thereby reducing the water stress of plants, which require less energy to move and absorb water.

Saturated hydraulic conductivity (Ksat) is a hydrologic flux parameter commonly used to determine water movement through the saturated soil zone. Understanding the influences of land-use-specific Ksat on the model estimation error of water balance components is necessary to advance model predictive certainties and land management practices. An exploratory modeling approach was developed in the physically based Soil and Water Assessment Tool (SWAT) framework to investigate the effects of spatially distributed observed Ksat on local water balance components using three digital elevation model (DEM) resolution scenarios (30 m, 10 m, and 1 m). All three DEM scenarios showed satisfactory model performance during calibration (R2 > 0.74, NSE > 0.72, and PBIAS ≤ ±13%) and validation (R2 > 0.71, NSE > 0.70, and PBIAS ≤ ±6%). Results showed that the 1 m DEM scenario provided more realistic streamflow results (0.315 m3/s) relative to the observed streamflow (0.292 m3/s). Uncertainty analysis indicated that observed Ksat forcings and DEM resolution significantly influence predictions of lateral flow, groundwater flow, and percolation flow. Specifically, the observed Ksat has a more significant impact on model predictive confidence than DEM resolution. Results emphasize the potential uncertainty of using observed Ksat for hydrological modeling and demonstrate the importance of finer-resolution spatial data (i.e., 1 m DEM) applied in smaller watersheds.

Soil physicochemical properties and macropore spatial structure affect saturated hydraulic conductivity (Ks). However, due to regional differences and long measurement time, Ks is tedious to quantify. Therefore, it is of great importance to find simplified but robust methods to predict Ks. One possibility is to use pedo-transfer functions (PTFs). Along this line, stratified sampling was carried out in six typical forestlands in the rocky mountain area of Northern China. Penetration experiments and industrial CT scanning were combined to explore the distribution characteristics of regional Ks and its influencing factors. Based on this, we compared three Ks PTF models by multiple linear regression for Ks prediction. The results indicated that: (1) Ks decreased with increasing soil depth, which followed the order coniferous forest < broad-leaved forest < mixed forest, and the change range of mixed forest was greater than that of homogeneous forest. (2) Soil bulk density, water content, sand, silt, organic matter, total nitrogen, total phosphorus, and total potassium were significantly correlated with Ks (p < 0.05). In addition, stand type and soil depth had a certain impact on soil physicochemical properties that affected Ks. (3) Soil macropore structure, such as number density, length density, surface area density, and volume density, all decreased with increasing soil depth. They were all significantly positively correlated with Ks (p < 0.001). (4) The best predictability and universality for PTFs was achieved for PTFs containing bulk density, organic matter content, and total phosphorus. Only PTFs containing parameters of macropore spatial structure did not yield high predictability of Ks. The findings of this study contribute to the understanding of forest hydrological infiltration processes in rocky mountain forests in Northern China, and provide theoretical support for the prediction and management of water loss and soil erosion and the enhancement of water conservation functions.

Vadose zone acts as a controlling agent for recharge and transport of contaminants into aquifers. Hence, for modelling and quantifying flow and transport processes in subsurface environments, hydraulic conductivity ( K ) of the vadose zone plays an important role. However, given the heterogeneity and anisotropy of subsurface systems, the in-situ measurement of K is a daunting task at a larger scale. The present study was conceived to evaluate the efficacy of salient pedotransfer functions (PTFs) to indirectly estimate the saturated hydraulic conductivity ( K s ) of a lateritic vadose zone of eastern India. Also, in-situ hydraulic conductivity along with basic soil physical properties was determined in different vadose-zone layers at three locations (bare plot, cultivated field and orchard). Four PTFs [Campbell, Rawls–Brakensiek/Cronican–Gribb (R–B/C–G), and Models 2 and 3 of Rosetta] were selected to estimate K s and their performances were evaluated. Based on the statistical indicators, it is concluded that Model 3 of Rosetta is capable of predicting relatively close values of K s for the lateritic vadose zones to some extent. To generalise the findings of this study, it is recommended that such field-based studies should be carried out at a larger scale in lateritic terrains with varying land use/land cover.

【Objective】Freeze-thaw cycles are a critical abiotic process that reshape soil structure. This study investigates their impact on the saturated hydraulic conductivity of soil in an open-pit coal mine in Haizhou, which is reclaimed with different vegetation types. 【Method】A laboratory experiment was conducted in spring. The vegetation types studied included Ulmus pumila forestland, Rhus typhina forestland, farmland, and waste grassland. Soil samples from the top 0-20 cm soil layer was used in the experiment. The natural spring thaw environment was simulated using a constant temperature test chamber. Infiltration tests were performed with a ring infiltrometer. The saturated hydraulic conductivity was analyzed under different freeze-thaw cycles, thawing times, and before and after freeze-thaw treatments.【Result】① The saturated hydraulic conductivity decreased with increasing freeze-thaw cycles and thawing time. It also varied with vegetation type and their interactions. The saturated hydraulic conductivity measu

Spatial heterogeneity in soil properties has been a challenge for providing field-scale estimates of infiltration rates and surface soil moisture content over natural fields. In this study, we develop analytical expressions for effective saturated hydraulic conductivity for use with the Green-Ampt model to describe field-scale infiltration rates and evolution of surface soil moisture over unsaturated fields subjected to a rainfall event. The heterogeneity in soil properties is described by a log-normal distribution for surface saturated hydraulic conductivity. Comparisons between field-scale numerical and analytical simulation results for water movement in heterogeneous unsaturated soils show that the proposed expressions reproduce the evolution of surface soil moisture and infiltration rate with time. The analytical expressions hold promise for describing mean field infiltration rates and surface soil moisture evolution at field-scale over sandy loam and loamy sand soils.