Hydrological Processes最新文献

Quantifying tree transpiration variability across soil volumetric water content (VWC) is vital for understanding tree water use strategies and developing effective forest management in dryland areas. However, the complicated interaction of soil moisture and meteorology on tree water use is still indistinct, resulting in challenges for water resource management in arid and semiarid regions. To examine the impacts of environmental factors on tree water use, canopy transpiration (T) and canopy conductance (G_c) of Platycladus orientalis plantation were quantified through Granier-type thermal dissipation probes and the Penman-Monteith equation, respectively, in a semiarid area of the Loess Plateau throughout the growing seasons (May–September) of 2020–2022. Average T increased with increasing VWC, while the peak value and growth rate of T decreased due to relatively low vapour pressure deficit (VPD) even when VWC was at the highest level (0.105–0.127 m³ m⁻³). The ratio of stomatal sensitivity to reference G_c decreased from 0.89 to 0.52 with increasing VWC, indicating a shift from more to less strict stomatal regulation. The decoupling coefficient increased simultaneously with rising VWC, indicating an enhanced effect of solar radiation (R_s) and a decreased stomatal limitation on transpiration. VWC exceeded 0.094 m³ m⁻³ in more than 50% of the instances. Under these conditions, there was a significant increase (p < 0.05) in the sensitivity of G_c to VPD and R_s as VWC increased. These results suggest that P. orientalis adapts to drought by reducing stomatal conductance and water loss through transpiration during soil droughts. Given increasing drought events and accelerated soil water depletion in the arid region, heightened water stress will impair tree gas exchange and hinder vegetation growth. This study reveals an adaptive mechanism of P. orientalis in semiarid areas and advances understanding of plant water use strategies in water-limited ecosystems. Given frequent droughts and increasing soil water depletion worldwide, extra attention on drought impacts on the water use of forests is crucial in the Loess Plateau and similar drought regions.

We investigated the influence of landslide deposits on hydrologic connectivity and subsurface water movement in small headwater catchments in the Western Cascades, Oregon, USA. We examined isotopic variations in surface water across multiple catchments, comparing wet and dry periods to assess how antecedent moisture influences hydrologic connectivity and groundwater interactions. Seasonal shifts in δ¹⁸O values reveal that hydrologic connectivity increases during wet conditions, resulting in more uniform isotopic signatures across catchments due to enhanced vertical and lateral water movement in the subsurface. In contrast, during dry periods there was greater spatial variability in δ¹⁸O, reflecting localised groundwater contributions and reduced connectivity. Notably, some catchments with high proportions of earthflow terrain maintain consistent water isotopic ratios across seasons, suggesting persistent groundwater inputs from landslide deposits. Spatial patterns in δ¹⁸O also point to subsurface inter-catchment flow paths facilitated by landslide deposits. Streamflow measurements during the dry season further support these findings. Catchments underlain by older, stabilised landslide deposits had highly variable unit discharge and frequent periods of flow cessation, consistent with weaker subsurface connectivity and limited water retention. In contrast, catchments draining active earthflows maintained relatively high unit discharges and perennial flow, indicating stronger subsurface linkages and greater potential for water accumulation that sustains both flow and ongoing slope movement. We estimated storage potential within landslide deposits and then used this to estimate catchment storage potential. Catchment storage was negatively correlated to variability in isotopic ratios, indicating an inverse relationship between catchment storage and variability in water sources in both space and time. Overall, our results demonstrate that geomorphic setting—particularly the presence and structure of landslide deposits—can exert strong control on the spatial distribution of hydrologic connectivity in mountain catchments. These insights improve our understanding of how subsurface properties mediate water movement and streamflow resilience under varying climate conditions.

Significant advancements have been made in vegetation restoration and ecosystem rehabilitation on the Loess Plateau, China. Previous studies have mainly focused on runoff and erosion in different vegetation types (trees, shrubs, and herbaceous plants), with few studies using hydrodynamic parameters to explain the flow and sediment reduction effects of the tree canopy, litter layer, and root layer. Using an artificial soil tank, the runoff and sediment yields of vegetation at each level (litter layer (LL), canopy layer (CL), bare soil layer (RL), and composite layer (litter + canopy) (SC)) were investigated under different rainfall intensities (RI) (30 and 90 mm/h) and slopes (S) (10° and 15°). The effects of hydrodynamic parameters on erosion were analysed by the structural equation model. The runoff rate of RL was the highest, with an average value of 0.37 L/min (RI: 30 mm/h; S: 15°). The litter and composite layer had the greatest reduction effects on slope erosion (75.66%–92.94%), whereas the reduction rate of slope erosion by the canopy layer was 14.27%–63.94%. Under different rainfall and slope conditions, the cumulative runoff of RL was the largest. Except at an RI of 30 mm/h and an S of 10°, the cumulative runoff of LL plots was the smallest, indicating that litter plays an important role in reducing slope runoff. Based on the structural equation model, the influence coefficients of the Froude number (Fr) on runoff and erosion are −0.28 and −0.31, respectively. This study provides quantitative evidence for optimising vegetation allocation strategies and a scientific basis for ecological protection in the Yellow River Basin.

Controls of hydrology, landscape and soil characteristics on redox potentials, particularly at fine spatial and temporal scales, are poorly quantified and understood. Using high-frequency sensors (30 min), the variability of redox potentials (Eh) in riparian soils was investigated for multiple depths and across diel, event and seasonal time scales over a period of 2 years. Sampling was performed for two riparian sites upstream of dams with contrasting soil textures. Incremental changes in soil moisture triggered abrupt and disproportionately large shifts in soil Eh values, a threshold-like behaviour that has not been reported before. Contrary to expectations, Eh values initially decreased as the soil dried and then abruptly increased with further drying and oxidation of soil. Diel Eh patterns differed between sites, with the sand-rich site oxidising by day and reducing at night, while the clay- and silt-rich site showed the opposite pattern. These differences were attributed to differential oxygen diffusion and consumption by processes such as photosynthesis, evapotranspiration and microbial respiration. Sharp Eh shifts also occurred at soil depths with textural discontinuities. These redox hot spots and hot moments were attributed to differences in site topography, hydrology and soil characteristics such as texture, moisture, organic matter content and microbial biomass. Identifying and understanding these fine-scale spatial and temporal patterns of Eh is critical for improved characterisation and quantification of biogeochemical processes in redox-sensitive environments. This study underscores the value of high-frequency redox sensors in making such assessments.

This study examines the hydrogeochemical characteristics and groundwater interactions across diverse aquifer systems in Palakkad, a water-stressed and rapidly urbanising district in Kerala, southern India. Despite its significant dependence on groundwater, urbanisation has a profound impact on hydrological processes, particularly on groundwater quality and availability. This influence is mediated by local geology, where hard-rock aquifers present hydrogeological complexities despite their storage capacity and contamination resistance. Understanding the interplay between urban development and groundwater quality through region-specific studies is crucial, given the hydrochemical variations across different rock types. Using multiple analytical and geochemical modelling approaches, groundwater in Palakkad is classified as freshwater, predominantly of the calcium-bicarbonate type, with most chemical parameters meeting WHO drinking water standards. Geochemical analysis reveals a cation dominance of Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ and an anion dominance of HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻ > F⁻. Groundwater chemistry is primarily controlled by geogenic processes, with rock–water interactions and reverse ion exchange being the dominant mechanisms. Key processes include the dissolution of silicate minerals, particularly ferromagnesian minerals and plagioclase feldspar, alongside contributions from secondary mineral precipitation (calcium carbonate, clay minerals), gypsum dissolution and cation exchange in soils. These findings highlight that urbanisation's impact on hard-rock aquifers involves complex interactions among geology, land-use changes and hydrochemistry, extending beyond merely reduced recharge or direct contamination of aquifers. This underscores the critical importance of incorporating local geological and hydrogeochemical knowledge to develop effective and sustainable urban water management strategies, with significant implications for groundwater resource management in rapidly urbanising regions worldwide.

Coniferous forests are one of the more ubiquitous forests on Earth. The needles in their canopy and on the land surface can cut falling raindrops, thereby altering rainfall characteristics. These characteristics strongly affect forest rainfall evaporation, under-canopy soil moisture and soil erosion. The cutting effect should be critically controlled by the needle diameter, raindrop diameter and impacting velocity. In this study, a high-speed camera system, coupled with a drop staining method, was used to systematically investigate the effect across five needle diameters, five raindrop diameters, and two falling heights. The pre- and post-cutting raindrop characteristics and needle properties were analysed. Our results show that cutting reduced drop velocity and diameter by 22% and 61%, respectively. For a given needle diameter, the ratio of change in drop velocity decreased as drop diameter increased. These changes caused a 58% decrease in total drop energy. Needle diameter influenced the distribution of post-cutting raindrop numbers, with larger needles causing a higher proportion of smaller drops. For different needle diameters, cutting reduced drop diameter, velocity, and mean energy by 75%, 23% and 91%, respectively. The effects increased linearly with needle diameter. However, the total raindrop water mass, partially reflecting water retention on the needles, decreased with increasing needle diameter. Analyses revealed that the influence of different needles was closely linked to their apparent flexural strength. Our results also reveal that the cutting effect remained significant even at a falling height, which generated a drop falling velocity similar to natural rainfall. These findings underscore the critical role of the needle-cutting effect in modifying throughfall dynamics and highlight the need to incorporate it into models of sub-canopy hydrological and ecological processes.

Estimating catchment-scale evapotranspiration remains a difficult problem in hydrology. This study introduces a new approach on the basis of the Maximum Entropy Production (MEP) principle, which has been applied for point estimations in earlier studies. The expansion to the catchment scale is achieved by adopting the simplified MEP method and parameterization to reflect the heterogeneity in the catchment. To obtain references for the latter, the flux tower data are studied. The method is applied to a Korean catchment in two tracks of utilising satellite remote sensing and ground data. The proposed approach allows the calculation of all heat fluxes, including the latent heat flux, that is, evapotranspiration. The estimated evapotranspiration is well compared with the global product of the Penman-Monteith-Leuning model as well as the annual water balance, derived from ground-measured precipitation and runoff. An appropriate temperature estimation, representative of the catchment, is found the priority for better performance. Our study shows that the MEP-based method is found a promising option for estimating catchment-scale evapotranspiration, whilst allowing users to utilise either ground measurement or satellite data, depending on availability.