Hydrological Processes最新文献

Modelling volumetric water content and fluxes in unsaturated soils is fundamental to land surface-groundwater coupling simulations. Richards equation (RE) provides relatively accurate predictions of soil moisture due to its fundamentally sound physical basis. However, numerical solutions of RE are often computationally demanding and can be challenging to obtain under highly variable hydro-climate conditions due to its high nonlinearity, especially when used in large-scale hydro-climate applications. By adopting the integrated form of RE, this paper presents a Layer-Averaged solution of RE (LARE) to simulate volumetric water content and fluxes in stratified soil profiles. To this end, a coupled system of ordinary differential equations was developed, which addresses complex hydroclimate boundary conditions at the soil surface and dynamic water table conditions at the soil bottom. The model was verified by comparison against analytical solutions, HYDRUS 1-D, and finite difference schemes for homogeneous and heterogeneous soil profiles. Robustness of the model to reproduce and interpret real field was demonstrated under real time-variable hydrometeorological conditions imposed at the soil surface. Uncertainty bounds for model simulated volumetric water content were constructed using the Bayesian Monte Carlo method, revealing that hydrometeorological inputs and model structural errors were major source of predictive uncertainty and the contribution of parametric uncertainty was marginal. The accuracy and numerical efficiency of LARE makes it a suitable, alternative numerical scheme for solving RE at finer spatial resolution and at sufficiently coarser resolutions. The model has the potential to be integrated into land surface models for large-scale watershed soil moisture dynamics simulations.

The influence of precipitation types on isotopic composition has been extensively studied, with foci on the distinct isotopic signatures of convective and stratiform precipitation. The typhoon precipitation system is characterised by pronounced convective processes alongside stratiform influences. Such a system provides a unique opportunity to advance the mechanistic understanding of isotopic fractionation during Typhoon Rai (December 2021). In this study, we analysed hourly precipitation samples collected in Fuzhou, Southeastern China, during Typhoon Rai to elucidate stable isotope signatures associated with distinct precipitation types. Our results revealed significant fluctuations in δ¹⁸O values (−9.24‰ ± 3.80‰, mean ± SD; range: −2.75‰ to −13.29‰), exhibiting a typical two-stage variation pattern. During the first stage, as the typhoon approached the sampling site, rainfall δ¹⁸O progressively decreased from −2.75‰ to −12.62‰, driven mainly by intense convective precipitation and subsequent rainout processes. During the second stage, isotopic values stabilised at −13.29‰, reflecting a shift to the stratiform-dominated precipitation. This stabilisation was attributed to post-convective stratiform development (i.e., anvil clouds), which had inherited an extremely depleted δ¹⁸O signature and was further modified by cloud microphysical fractionation processes. These findings highlight the critical role of precipitation types in governing isotopic variability during typhoon events, offering new insights into the complex interplay between dynamic and microphysical processes in future strong tropical cyclones.

Research studies on floods are often reliant on Soil Conservation Service Curve Number (SCS-CN) values from SCS-CN tables for loss estimation because of their simplicity. However, table values are highly subjective. Infiltration models have been used in several studies for the analysis of in situ double-ring infiltrometer tests. A relationship between soil parameters and CN could not be derived from these studies. However, this relationship is essential for improved rainfall-runoff predictions. In total, 25 double-ring infiltrometer tests were conducted in basins of Jazan Province for the characterisation of soil parameters. The infiltration models (Horton, Philip, and Green–Ampt) demonstrated effective analysis of the data, with no significant differences observed among them. A model has been proposed to describe the temporal evolution of the CN from its initial to ultimate states. In the initial infiltration, CN values ranged from 25 to 51, and between 39 and 68 in the ultimate infiltration. The range of CN estimated from the ultimate infiltration (saturated hydraulic conductivity) was 39 and 68. The ultimate values were validated using observed CN from observed rainfall-runoff events in the alluvium of Wadi Liyyah, which ranged from 38 to 70 at abstraction ratios, λ = 0.01 and λ = 0.2, respectively, with 99% confidence. Therefore, the study recommends the use of ultimate infiltration to estimate the SCS-CN in flood simulation studies in this region.

Ice thickness is a key parameter reflecting the structural stability of ice covers and the magnitude of ice loads. Therefore, accurately predicting river ice thickness is essential for the safety assessment of bridge engineering and the formulation of emergency plans. To enhance the accuracy of ice-thickness prediction, this study proposes an improved one-dimensional thermodynamic model based on the traditional formulation, which explicitly accounts for the effects of longwave radiation flux and turbulent fluxes. To prove the reliability of the presented model, comparative analyses were conducted using in situ observations from the Songhua River against the Ashton model, the Ding model and the conventional one-dimensional thermodynamic model. The results indicate that, compared with the measured ice thickness, the average absolute errors of the predicted ice thicknesses by the Ashton's thermodynamic model, Ding's thermodynamic model, traditional one-dimensional thermodynamic model and the improved model are 4.72, 4.69, 21.46 and 3 cm, respectively, demonstrating that the proposed model achieves the highest prediction accuracy. The improved model demonstrates superior applicability, primarily due to the incorporation of the energy balance equation and heat conduction equation, which comprehensively consider the bidirectional heat transfer between the upper and lower boundaries of the ice layer. Overall, the findings of this study provide a robust methodological foundation for quantitatively describing river-ice evolution in cold regions and offer scientific support for the safety assessment and emergency management of hydraulic and bridge structures in icy environments.

Poyang Lake wetland serves critical ecosystem functions such as water regulation, carbon sequestration, and biodiversity protection. However, the impoundment of the Three Gorges Dam has markedly influenced the local hydrological processes and vegetation growth in recent years. To quantify these changes, we applied 20-year Landsat and MODIS observations to produce a synthetic normalised difference vegetation index (NDVI) product with 8-day revisit frequency and 30-m spatial resolution. Using this product, we depicted a comprehensive 20-year monitoring picture of the spatiotemporal evolution of hydrological patterns and net primary productivity (NPP) in Poyang Lake. Then, the impacts of early-water recession on hydrological patterns, vegetation NPP, and phenological characteristics were documented. Finally, we investigated the influence of hydrological alteration-induced vegetation dynamics on waterbird habitat suitability. The results showed that 22.13% of the lake area experienced a significant increase in the annual emergence duration over 20 years, and this increasing trend was particularly prominent in autumn, with 33.37% area proportion. The annual NPP experienced a consistent increase (6.85 gC·m⁻²·yr⁻², p > 0.05) during 2000–2019. With regard to seasons, autumn NPP presented the largest increasing trend, and the increasing area accounted for 36.65% of the lake's floodplain. Early-dropped water levels lead to an earlier start of the growing season in Carex communities in the lower lake center, resulting in a significant increase in autumn NPP (7.41 gC·m⁻²·yr⁻², p < 0.05) and high-quality food resources in October and November. However, the shift to the earlier peak of the growing season accelerated the normal rate of vegetation senescence and caused a significant decrease in food quality when the foraging requirements peaked in December (−0.15 gC·m⁻²·yr⁻², p < 0.01) and January (−0.11 gC·m⁻²·yr⁻², p < 0.01). In addition, the combined effects of a prolonged dry season and extensive fishery may threaten the stability of the Phragmites community, thus reducing the effectiveness of biodiversity conservation in the nature reserves. These results provide a critical reference for local authorities to optimise hydrological management and biodiversity conservation in the Poyang Lake wetland.

Splash erosion (SER) is a key stage of soil erosion, and bedrock fissures in the karst area makes the erosion situation complex. However, the effects of different bedrock fissure ratios (BFRs) on SER in karst area have not yet been reported. We investigated the effect of five BFRs (0%, 1%, 2%, 3% and 4%) changes on SER under three slope gradients (10°, 15° and 20°) and one rainfall intensity (1.5 mm min⁻¹) in the karst area using simulated rainfall experiments. Single simulated rainfall event lasted for 18 min. The outcomes confirm that as the BFRs increased, the upslope splash erosion (USER), downslope splash erosion (DSER) and total splash erosion (TSER) increased. Surface runoff showed no statistically significant variation across different BFRs and slope gradients, but fissure runoff at 4% BFR was highest for all slopes. BFR was significantly correlated with the fissure runoff, USER, DSER and TSER at 15° and 20° slopes. Our results underscore the greater the BFRs, the greater the SER in karst slope. This work contributes to advancing knowledge about how BFRs impact SER in thin karst soil layers.

Groundwater–surface water exchange plays a fundamental role in the transport of energy and solutes in coastal salt marshes, which are positioned at an intersection between terrestrial and marine hydrologic environments. Hydraulic gradients in shallow marsh sediments continuously change due to tidal water level variations that alternately flood and drain the marsh platform, often superimposed on terrestrial groundwater drainage. We use timeseries data from Vertical Temperature Profiler and Conductivity-Temperature-Depth instruments to investigate the space–time patterns of groundwater–surface water exchange at a hillslope-adjacent fringing salt marsh on the Herring River in Wellfleet, MA. Analyses of data acquired from September to December 2023 demonstrate that time-averaged exchange rates systematically vary from recharge near the tidal channel to saline groundwater discharge towards the upland fringe and systematically decrease during the transition from summer to winter conditions. Exchange rates were continuously modulated by tides, including high-frequency compound and harmonic components generated by non-linear interactions as the astronomical tide propagated into the estuary. The exchange rate sensitivity to tidal forcing decreased with both frequency and distance from the tidal channel, consistent with the lateral diffusion of pore pressure perturbations through the high permeability layer underlying the surficial, low permeability peat. We find that tidal loading of the marsh sediments is a two-stage process consisting of direct, instantaneous loading during inundation and indirect, time delayed loading via lateral diffusion of pore pressure variations in-between inundation intervals. The combination of terrestrial groundwater entering the marsh through the high permeability layer beneath the peat, seawater flooding the marsh platform during inundation, and tidally induced pore pressure variations diffusing into the marsh generates a complex space–time exchange pattern, including bi-directional exchange at tidal periods, with poorly understood but important implications for biogeochemical processes in the marsh sediments and constituent fluxes to the coastal ocean.