Hydrological Processes最新文献

Accurate rainfall–streamflow observations are essential for understanding runoff generation and flood hazards in mountainous regions. Yet such information remains scarce in many areas, especially for small and medium-sized catchments in tropical environments of developing countries. This study develops high-resolution rainfall–streamflow datasets and evaluates the spatiotemporal variability of rainfall–runoff dynamics to assess the applicability of the rational method, from its empirical formulation to its physical interpretation, for flood-hazard management in the Nyamutera (44 km²) and Gaseke (109 km²) catchments of the mountainous Mukungwa watershed in northwestern Rwanda. To address data scarcity, cost-effective stream monitoring stations were installed to record flow depths, complemented by three automatic rain gauges and two weather stations that record rainfall and other weather parameters at 15-min intervals. Periodic discharge measurements were conducted to establish stage–discharge rating curves, which were used to derive continuous streamflow records from April 2022 to May 2023. Analysis of 40 storm-event responses revealed marked contrasts between the catchments: Nyamutera produced higher runoff coefficients (0.05–0.40; mean = 0.20; annual mean = 0.18) than Gaseke (0.02–0.35; mean = 0.10; annual mean = 0.11), reflecting its steeper slopes and lower storage capacity. Design runoff coefficients for the 100-year event were 0.55 and 0.51, and recorded peak discharges reached 131 and 122 m³/s, respectively. These values reflect Nyamutera's faster, more concentrated flow pathways, in contrast to the more attenuated response observed in Gaseke. The results highlight differences in runoff behaviour between the two catchments, likely reflecting their contrasting topography, soil properties and storage capacity. Although the monitoring network captured most dynamics, uncertainties remain in monitoring very low flows, extreme peaks and high rainfall variability. This study suggests additional monitoring techniques that could help capture these conditions. The developed approach provides a practical, transferable framework for rainfall-streamflow characterisation in similarly data-limited mountainous environments.

Accurately partitioning evapotranspiration (ET) into evaporation (E) and transpiration (T) remains challenging, but is essential for understanding ecohydrological processes and sustainable management of water resources. This study aims to partition ET and investigate the land use change effects on ET components through a space-for-time substitution approach and an optimised isotopic tracing method on China's Loess Plateau. The soil samples up to 20 m deep were collected from farmland (F) and two vegetation types converted from F, that is, 13-year-old peashrub (P13) and 51-year-old apricot (A51). By using multiple isotopes (δ²H, δ¹⁸O and ³H), ET was efficiently partitioned to discuss the effects of land use change on soil water balance (SWB) components. Following the conversion of F to P13 and A51, soil water storage declined by 44% and 39%, respectively, while deep drainage was completely eliminated in both cases. ET partitioning revealed that P13 and A51 exhibited significantly higher ET (511.7 and 411.6 mm year⁻¹, equivalent to 131% and 107% of mean annual precipitation) than F (372.5 mm year⁻¹, equivalent to 96% of mean annual precipitation). Further, E slightly decreased in P13 and A51 by 10% and 7% (7.0 and 4.6 mm year⁻¹); whereas T significantly increased by 48% and 16% (146.2 and 49.7 mm year⁻¹), respectively. T dominated ET under the three land uses with T/ET ranging from 82% to 89%, which is explained by lower precipitation and greater tree age in the sample plots of this study area. The quantified SWB well revealed the mechanisms by which land use change affects soil hydrological processes. The findings can provide valuable insights for ecological restoration and water resource protection in arid and semi-arid regions.

Although runoff is usually quantified as a fraction of annual rainfall, its spatial heterogeneity and temporal variability are critical aspects poorly assessed in flat drylands. In this study, we: (i) quantified the annual runoff and its relation with watershed and piosphere (high cattle impact) areas, (ii) quantified the uneven contribution of the largest rainfall and runoff events to their respective yearly totals at different temporal scales, (iii) evaluated the runoff responses to rainfall characteristics (event size and intensity), and (iv) quantified the lag time between rainfall and runoff peaks and its relation to the maximum length of the watershed. To do this, we combined high-resolution field measurements (three consecutive years, 15-min resolution) with remote-sensing analyses for six watersheds (sizes between 20 and 2000 ha) in Dry Chaco rangelands (Argentina). On average, runoff was not explained by watershed or piosphere area. Runoff was more variable than rainfall: the 10 wettest days explained 100% and 60% of annual runoff and rainfall, respectively. Only 15% of the rainfall events generated runoff. Runoff required on average the coincidence of a 20.3 ± 1.6 mm rainfall size and 12.2 ± 2.2 mm h⁻¹ rainfall intensity. Above these thresholds, the response between rainfall and runoff was linear (R² > 0.66 and 0.62 for event size and intensity, respectively). Lag was 43 ± 27 min, highlighting the ephemeral flash-flood nature of runoff. There was also a linear relationship between mean lag and watershed's maximum length (r = 0.87). Our results highlight the stochastic nature of runoff for Dry Chaco rangelands, both in space and time, modulated by rather subtle watershed physical elements and microtopography. This view challenges the idea of a fixed runoff generation area, which needs to be replaced by a more flexible, if not idiosyncratic concept, based on the interactions between terrain features and rainfall event characteristics.

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.

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.

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.