Runoff Yield Research Articles

Study on Functional Effectiveness of Soil and Water Conservation Measures in Rubber Plantations on Hainan Island

In rubber plantations, understory coverage is often disrupted by human activities, which increases the risk of soil erosion under intense rainfall typical of tropical islands. Evaluating the effectiveness of soil and water conservation measures (SWCMs) is crucial for effectively conserving subcanopy resources. This study focused on Hainan Island’s rubber plantations, where nine different SWCMs were implemented, and the runoff and sediment yield were monitored during the rainy season using runoff plots. Through correlation analysis, we identified the primary rainfall characteristic factors leading to soil and water loss on rubber plantation slopes. Path analysis was then used to quantify the impacts of these characteristic factors. The results showed that the SWCMs were significantly more effective in erosion reduction (68.55%) than in runoff reduction (58.95%). Of all the measures, comprehensive SWCMs proved most effective in controlling runoff (71.34%), followed by engineering SWCMs (62.03%) and biological SWCMs (43.51%). Comprehensive SWCMs were also found to be effective in erosion reduction, with a rate of 77.84%, surpassing engineering and biological SWCMs by 7.23% and 20.66%, respectively. Notably, the combination of narrow terraces, contour trenches, and grass planting was the most effective, achieving runoff-reduction rates of 80.94% and erosion-reduction rates of 85.27%. This combination is recommended as a primary prevention method. Rainfall and maximum 30-min intensity (I30) were identified as key variables affecting the efficacy of SWCMs, with rainfall positively correlating with runoff yield and I30 being more closely linked to sediment production. This study provides valuable insights for developing erosion control strategies for sloping garden lands in similar regions and lays theoretical foundations for future ecological restoration projects.

The effect of dynamic changes in vegetation coverage on the mechanism of organic carbon loss in inter-rill erosion

The intricate effects of dynamic variations in vegetation coverage, representing different vegetation growth states and erosion conditions, on properties (content, enrichment and loss) of sediment and soil organic carbon (SOC) fraction in inter-rill erosion have not yet been fully elucidated. By setting micro-plots with different vegetation coverage ranges (0 %, 15 ∼ 35 %, 25 ∼ 55 % and 35 ∼ 70 %), the interaction mechanisms between vegetation coverage and inter-rill erosion, particle size distribution and SOC fractions properties during the vegetation growing period were studied. The average sediment yield, runoff yield and sediment concentration were highest under the bare plot, and diminished progressively with increased vegetation coverage. The effective clay content decreased with the increasing coverage, while ultimate clay was highest in the vegetation coverage range of 25 ∼ 55 %. Clay particle was transported as aggregates, with enrichment for all treatments except for the vegetation coverage range of 35 ∼ 70 %, providing transportation potential for SOC fractions loss. The content of SOC and mineral-associated organic carbon, as well as their enrichment ratio, decreased and then increased with coverage, which is the opposite of particulate organic carbon, and the loss of all fractions decreased with increasing vegetation coverage. Mineral-associated organic carbon dominated change in SOC, with proportion in SOC content and loss decreasing first and then increasing with vegetation coverage. The structural equation model showed the impact of vegetation coverage on SOC fraction loss was mainly achieved through indirect regulation of inter-rill erosion and particle size distribution. Our results provide new insights into the complex relationship between natural slope vegetation coverage and SOC loss, particularly from a fractions perspective, as well as understanding the ultimate fate of SOC in such environments.

Evaluation of the EUROSEM on soil erosion simulation for loess plateau, northern China

AbstractThe Loess Plateau region features fragmented landforms, sparse vegetation, and short but intense summer rainstorms that can easily cause severe soil erosion. To evaluate its applicability to a typical Loess Plateau in northern China, an indoor laboratory experimental study was conducted for events with different slope lengths (3, 4, and 5 m) and rainfall intensities (50, 60, 70, 80, 90, 100, 110, and 120 mm/h). EUROSEM (European Soil Erosion Model) was used to simulate the soil erosion process and predict both total runoff and sediment yield. The EUROSEM modeling results were compared with the observed experimental values and analysed to determine the performance of EUROSEM. The results and analysis showed that EUROSEM could effectively simulate the runoff processes. It produced better predictions for the total runoff yield than for the sediment yield, with Nash–Sutcliffe efficiencies of 0.9003 and 0.1820, respectively. The qualified rates of the RE (relative error) between simulated and observed values of the total runoff and sediment yield were 87.5% and 37.5%, respectively. Compared to the sediment yield under rainfall intensities of 50–80 mm/h, those under 90–110 mm/h had lower RE and higher NSE, which increased from −3.9 to 0.5. However, the modeling results deviated more from the experimental data at a rainfall intensity of 120 mm/h. According to this study, EUROSEM is a good fit for simulating the runoff and partial sediment yield processes of the Loess Plateau region's slopes. However, the accurate prediction of sediment yield still requires more research to achieve complete effectiveness using EUROSEM for typical and wide scenarios in China.

Numerical simulation study on the effect of underground drainage pipe network in typical urban flood

Rapid urbanization and climate change have heightened urban flood risks. An in-depth examination of the underground drainage pipe network’s effect on urban flood inundation can enhance urban stormwater management and mitigate disaster risks. This study presents a full hydrodynamic urban flood model (FHUM) coupling the pipe transport module of the Storm Water Management Model (SWMM) with a shallow water model. Based on unstructured grid cells, runoff yield and confluence calculations are carried out to effectively separate the underground drainage pipe network from other factors. The model is applied to Minzhi Area and Haidian Island to quantitatively assess the influence of the underground drainage system on urban flooding. Results indicate that FHUM performs well, accurately reflecting the process from rainfall to inundation. The underground drainage pipe network reduces surface inundation in the study area and improves the city’s stormwater drainage capacity. With increasing rainstorm intensity, the impact of the pipe network does not exhibit a consistent trend. During heavy rainstorms, the pipe network consistently plays a significant and stable role, particularly in reducing high inundation depths. However, attention should be paid to the potential flood risk transfer associated with using pipe networks in urban flood management. This work provides a scientific basis for urban stormwater management, holding significant importance in improving flood control and disaster reduction capabilities.

Gully regulates snowmelt runoff, sediment and nutrient loss processes in Mollisols region of Northeast China

Gully is a prominent indicator of land degradation in agroecosystems, functioning as a crucial pathway connecting upslopes to downstream channels. However, little is known about how gully regulates runoff, sediment, and nutrient loss processes in the catchment during snowmelt. In this study, we monitored these processes in situ at both the gully head (the upslope accumulated catchment of the gully head, CGH) and outlet of two representative and typical gully-dominated catchments (F1 and F2) during snowmelt in Mollisols region of Northeast China. Our results showed that runoff discharge of CGH and outlet exhibited a multi-peak trend during snowmelt, driven by the transition from snow melting to soil thawing. This transition resulted in distinct runoff patterns in both CGH and outlet, with significant differences in their response to air temperature. The total runoff yield of CGH accounted for 57.8 % in F1 and 40.6 % in F2 of the total runoff yield of the outlet. Notably, the peak sediment concentration displayed a marked lag compared to the peak runoff discharge, primarily dominated by the increased sensitivity of gully erosion after the thawing of gully slopes. Gully erosion was the main source of sediment yield in the catchment, contributing 98.2 % in F1 and 96.6 % in F2. Furthermore, nutrient concentrations exhibited a decreasing trend during snowmelt. The comparison of high nutrient concentrations in CGH and relatively low nutrient concentrations in outlet highlighted the gully's role in intercepting and diluting runoff nutrients. Hysteresis analysis confirmed the differential contribution of CGH and gully to nutrient sources. CGH accounting for 50.9 % and 93.3 % of runoff TN and runoff TP loss, while contributing only 8.3 % and 5.8 % to sediment TN and sediment TP loss, respectively. These findings offer valuable insights for effective erosion control and nonpoint source pollution management in gully-dominated agroecosystems during snowmelt.

The role of soil dispersivity and initial moisture content in splash erosion: Findings from consecutive single-drop splash tests

Dispersive soil is commonly associated with hydraulic erosion due to its tendency to disperse when in contact with water. Nevertheless, the erosion process of dispersive soil remains poorly understood. This study aims to explore the influence of dispersivity and initial moisture content on the splash erosion of dispersive soil, which is a crucial stage of hydraulic erosion. Consecutive single-drop splash tests were conducted on artificially prepared dispersive soil (made by adding sodium carbonate to the soil) with varying dispersivity levels and moisture contents. A high-speed and a single-lens reflex (SLR) camera were employed to capture the process of erosion in exquisite detail. The results demonstrated the significant influence of dispersivity on splash erosion. At moisture content below 20%, increased dispersivity weakened the splash erosion effect, leading to reduced infiltration, splashed soil mass, crater volume, and depth. Conversely, when the initial moisture content reached 20% or saturation, intensified dispersivity exacerbated splash erosion. Dispersivity also increased the sensitivity of the soil splash process to changes in moisture content. Dispersive soil exhibited greater sensitivity compared to non-dispersive soil, affecting the mass of splashed soil, soil-water mixture droplets area, water-soil mass ratio, and particle ejection distance. Dispersivity also caused splashed particles to fragment, resulting in more soil-water mixture droplets and a greater splash distance. Furthermore, dispersivity reduced infiltration ratio and increased runoff yield after erosion events, indicating a higher risk of transporting splashed soil particles through runoff. These insights contribute to erosion models and have practical applications in managing dispersive soil.

Environmental Regulation and Stormwater Management Strategies for an Urban River in Northwest China: A Sustainable Approach

Low-impact developments (LIDs) have emerged as effective strategies for mitigating the adverse impacts of urbanization on river environments. This study aims to enhance river environment quality by examining the effects of LIDs and land use/cover change (LUCC) in the context of river environment and hydrological conditions. Using the Stormwater Management Model (SWMM) in an urban river setting, the study investigates the impact of LIDs on urban river water volume. An analysis of river runoff quality and quantity is conducted, followed by the development of an optimal river water regulation scheme through a multi-objective ecological scheduling model. The results reveal that the incorporation of LIDs can substantially decrease river runoff yield for varying recurrence periods of design rainstorms. Consequently, the flood peak reduction rate ranged from 10% to 18%, and the flood volume experienced a reduction of 10–29% in the study area. The combination of river water regulation, LIDs and LUCC leads to a decrease in river water volume within the lower river channel by up to 47% especially in a typical dry year and dry season, accompanied by a decline in river flow velocity and water self-purification capacity. A risk-based multi-objective stochastic optimization model is employed to ensure sustainable management of urban river runoff in terms of both quantity and quality. This research contributes to the advancement of knowledge in sustainable basin management practices and offers practical insights for policymakers involved in the management of water resources and environmental conservation in semi-arid basins.

Optimizing Straw Mulching Methods to Control Soil and Water Losses on Loess Sloped Farmland

Straw mulching is a key method for controlling soil and water losses. Mulching costs may be reduced by applying it in strips rather than over entire areas. However, the effect of different straw mulching methods on the effectiveness of reducing soil erosion is unclear. In this study, the effects of straw mulching strip length (covering 1/4, 1/2, 3/4, and 4/4 of the slope length) and coverage rate (0.2, 0.5, and 0.8 kg m−2) on interception, infiltration, runoff, and soil erosion were investigated at the plot scale using rainfall simulation experiments. The further complex correlations between these variables were analyzed using structural equation modeling (SEM). Bare slopes were used as a control group. The rainfall intensity was chosen to be 60 mm h−1. The results showed that (1) the modified Merriam interception model can describe the change in interception with time under straw mulching conditions well (R2 > 0.91, NSE > 0.75). (2) A total of 35.39–78.79% of the rainwater is converted into infiltration on straw-covered slopes, while this proportion is 36.75% on bare slopes. The proportion of rainwater converted to infiltration was greatest (78.79%) when the straw covered 3/4 of the slope length at a coverage rate of 0.5 kg m−2, which was the most conducive to rainwater harvesting on the slope. (3) Straw mulching protects the topsoil from the impact of raindrops and directly affects the sediment yield (direct effect = −0.44). Straw mulching can also indirectly affect sediment yield by increasing interception, reducing runoff, and decreasing the sediment carrying capacity of runoff (indirect effect = −0.83). Compared with bare slopes, straw covering at least 1/2 of the slope length can significantly reduce runoff yield, but straw covering only 1/4 of the slope length can significantly reduce sediment yield. Moreover, once the straw mulch slope length reaches 3/4 and the coverage rate reaches 0.5 kg m−2, further increases in mulch slope length and coverage rate will not significantly reduce the runoff and sediment yields. These results assessed the effectiveness of different straw mulching methods in controlling soil and water losses on sloping farmland.

Technical note: Testing the connection between hillslope-scale runoff fluctuations and streamflow hydrographs at the outlet of large river basins

Abstract. A series of numerical experiments were conducted to test the connection between streamflow hydrographs at the outlet of large watersheds and the time series of hillslope-scale runoff yield. We used a distributed hydrological routing model that discretizes a large watershed (∼ 17 000 km2) into small hillslope units (∼ 0.1 km2) and applied distinct surface runoff time series to each unit that deliver the same volume of water into the river network. The numerical simulations show that distinct runoff delivery time series at the hillslope scale result in indistinguishable streamflow hydrographs at large scales. This limitation is imposed by space-time averaging of input flows into the river network that are draining the landscape. The results of the simulations presented in this paper show that, under very general conditions of streamflow routing (i.e., nonlinear variable velocities in space and time), the streamflow hydrographs at the outlet of basins with Horton–Strahler (H–S) order 5 or above (larger than 100 km2 in our setup) contain very little information about the temporal variability of runoff production at the hillslope scale and therefore the processes from which they originate. In addition, our results indicate that the rate of convergence to a common hydrograph shape at larger scales (above H–S order 5) is directly proportional to how different the input signals are to each other at the hillslope scale. We conclude that the ability of a hydrological model to replicate outlet hydrographs does not imply that a correct and meaningful description of small-scale rainfall–runoff processes has been provided. Furthermore, our results provide context for other studies that demonstrate how the physics of runoff generation cannot be inferred from output signals in commonly used hydrological models.

Determination of the minimum soil infiltration rate of sunken green space considering the annual runoff collection ratio, sunken depth and sunken green space area of Hefei city, China.

Sunken green space is one of the urban rainwater collection facilities, which belongs to Low Impact Development (LID) techniques. It plays a key role in the construction of sponge city, and the amount of runoff collection is usually affected by the area of the sunken green space, the infiltration rate of the soil, and the annual runoff collection rate. To determine the minimum soil infiltration rate of sunken green space considering the annual runoff collection ratio of sponge cities, this paper selects a residential district in Hefei city, China, as the case study. Based on 45 years of precipitation data, the designed rainfall corresponding to annual runoff collection ratios of 75%, 80% and 85% is 21.3 mm, 23.4 mm and 27.5 mm, respectively. The characteristics of rainfall infiltration in sunken green space are analyzed by using the water balance model and runoff yield and conflux model. The results reveal that the soil infiltration rate is 1.16×10-4 cm/s~3.88×10-3 cm/s when the sunken depth is 0.1 m~0.3 m and that the ratio of green space area is 5%~25%. The runoff collection of the reconstructed sunken green space is 2.87 times and 1.98 times that of the nonsunken green space and the nonreconstructed sunken green space, respectively. That is to say, under the comprehensive performance of the sunken depth, sunken green space area, the steady soil infiltration rater of the reconstructed sunken green space cannot be less than the value obtained in this paper. Otherwise, the requirements of annual total runoff reduction ratio of the sponge city cannot be met. Therefore, this study provides references for realizing the ratio of annual runoff collection and sponge city construction in similar urban areas. It can also be applied to optimal selection of sunken green space in some sponge city projects.

Runoff generation and erosion processes at the rock–soil interface of outcrops with a concave surface in a rocky desertification area

Rock surface flow, originating from outcrop surfaces during rainfall, represents a distinctive form of runoff influencing surface erosion and subsurface soil leakage in karst rocky desertification areas. Despite their significance, the processes governing runoff generation and erosion at the rock–soil interface (RSI) under the influence of rock surface flow remain poorly understood. This study aims to elucidate the generation and transformation of runoff at the RSI, along with their scouring erosion effects influenced by rock surface flow from concave-shaped outcrops. Artificial rainfall experiments were conducted on simulated rock–soil structural units featuring exposed rock surfaces and unexposed RSIs of outcrops with concave shapes. Two driving factors, namely rainfall intensity (R) and the inclination of the rock surface (IRS), were manipulated to investigate the formation and output processes of runoffs and sediments from the surface, RSI, and non-RSI (a site away from the RSI). The presence of an exposed rock surface altered the distribution pattern of rainfall–infiltration–runoff. An increase in the IRS led to a significant decrease in surface runoff (p < 0.05). When the IRS was close to vertical, the rainfall-runoff was primarily in the form of surface runoff; however, for inclinations less than 90°, the primary contributors to rainfall-runoff were the RSI and non-RSI runoffs. Surface soil erosion emerged as the predominant form of soil loss, with runoff yield demonstrating a linear positive correlation with sediment production. Both the IRS and R were identified as significant factors affecting surface runoff and soil erosion. Notably, when the IRS was less than 45°, the total soil loss reached its minimum. Therefore, runoff generation at the RSI led to a reduction in surface runoff and an increase in subsurface runoff, contributing to soil leakage at the RSI. Nevertheless, surface erosion remained the primary mechanism of soil loss.

Rock surface flow accelerates rill erosion of excavated slopes in karst mining areas

Rock surface flow is the secondary distribution of precipitation and inflow on the rock surface, an essential runoff generation mode in karst areas. The effects of rock surface flow on soil erosion in karst regions cannot be ignored. However, its impact on rill erosion in karst slopes remains unclear. The objectives of this study were to investigate the impact of rock surface flow on rill erosion, rill morphological characteristics, rill flow hydraulic characteristics, and hydrodynamic mechanisms. A field runoff plot (3 m long, 1 m wide and 0.3 m deep) with three inflow rates (2, 3, and 4 L/min) was subjected to runoff simulation experiments under two typical rock surface morphologies in karst areas: smooth rock surface (SRS) and karren rock surface (KRS), with bare slope (BS) as the control group. The results revealed that rock surface flow aggravated the soil and water loss of the excavated slope. Compared to BS, the runoff yield for SRS and KRS increased by 81.49 % and 61.91 %, respectively. Meanwhile, the soil loss of SRS and KRS were 2.50 times and 5.56 times greater. The rills below the rock outcrops didn’t develop into a rill network after formation, owing to the rock surface morphology. Rill depth was the best indicator of rill morphology for evaluating rill erosion on slopes below rock outcrops. The Reynolds number and Darcy–Weisbach resistance coefficient were the optimal hydraulic parameters to predict the rill erosion of the SRS and KRS, respectively. At the same time, the runoff power and flow shear stress were the best hydrodynamic parameters to describe the rill erosion mechanism of SRS and KRS. These results provide a scientific basis for further understanding the mechanism of soil erosion on karst slopes and for preventing soil erosion on karst slopes in mining areas.

Synergy between vegetation patterns and sedimentation has a temporal effect on water erosion in a slope‐gully system

AbstractMultiple soil and water conservation measures applied together perform better at reducing runoff and sedimentation than individual measures, which can be attributed to their synergistic effects on water erosion. However, whether these synergistic effects are always effective at reducing water erosion remains unclear. In this study, a series of physical models representing a slope‐gully system were tested to quantify the trend of synergistic effects of multi‐measure over time through simulated rainfall. The tested scenarios included four vegetation patterns on the slope—Pattern A: no grass, Pattern B: grass on the up‐slope, Pattern C: grass on the middle‐slope and Pattern D: grass on the down‐slope—and five levels of runoff path length decrease (RPLD) in the gully caused by sedimentation of a check dam (0, 1, 2, 3 and 4 m). Synergistic effects on runoff and sediment yields were influenced by vegetation patterns and RPLDs. Under the same vegetation patterns, synergistic effects increased with increase of RPLD. Under the same RPLD, the mean value of synergistic effects on runoff was in the following order: Pattern D (0.10%) &gt; Pattern C (0.09%) &gt; Pattern B (0.06%), and synergistic effects on sediment yields had a similar order: Pattern D (0.60%) &gt; Pattern C (0.42%) &gt; Pattern B (0.22%). Under Pattern B, based on the Mann–Kendall trend test, the synergistic effects on the runoff yields decreased over time. Contrastingly, under Patterns C and D, the synergistic effects on the runoff yields increased over time. The results show that the synergistic effect has time effect, and its change trend is related to vegetation patterns. Additionally, the results suggest that the middle‐ and lower‐slopes should be prioritized when restoring vegetation as the synergistic effects on runoff tend to increase when these have good vegetation cover.

Effect of microrelief features of tillage methods under different rainfall intensities on runoff and soil erosion in slopes

Tillage methods play a crucial role in controlling rainwater partitioning and soil erosion. This study utilized rainfall simulation experiments to investigate the impact of four tillage methods (manual digging (MD), manual hoeing (MH), traditional ploughing (TP), and ridged ploughing (RP)) on runoff and soil erosion at the plot scale. The smooth slope (SS) was used as a benchmark. Rainfall intensities of 30, 60, 90, and 120 mm h−1 were considered. The study revealed that tillage altered rainwater distribution into depression storage, infiltration, and runoff. Tillage reduces runoff and increases infiltration. The four tillage methods (30–73%) increased the proportion of rainwater converted to infiltration to varying degrees compared to the SS (22–53%). Microrelief features influenced the role of tillage methods in soil erosion. Surface roughness and depression storage accounted for 79% of the variation in sediment yield. The four tillage methods reduced runoff by 2.1–64.7% and sediment yield by 2.5–77.2%. Moreover, increased rainfall intensity weakens the ability of tillage to control soil erosion. When rainfall intensity increased to 120 mm h−1, there was no significant difference in runoff yield among RP, TP, MH, and SS. Therefore, assessing the effectiveness of tillage in reducing soil erosion should consider changes in rainfall intensity. Additionally, the cover management (C) factor of the RUSLE was used to assess the effects of different tillage methods on soil loss. Overall, the C factor values for tilled slopes are in the order MH > TP > RP > MD with a range of 0.23–0.97. As the surface roughness increases, the C factor tends to decrease, and the two are exponential functions (R2 = 0.86). These studies contribute to our understanding of how different tillage methods impact runoff and soil erosion in sloped farmland and provide guidance for selecting appropriate local manual tillage methods.

Flood simulation using the hydrological model and the hydrological–hydrodynamic coupling model in a small watershed in semi-arid and sub-humid region, North China

Abstract Flood disasters occur frequently in semi-arid and sub-humid mountain watersheds, and their formation mechanism is affected by many factors, resulting in low simulation accuracy. The main purpose of this study is to evaluate the impact of adding actual river channel data on the accuracy of flood simulation. In order to obtain higher-resolution terrain data, an unmanned aerial vehicle (UAV) was used to survey the study area. Taking the Liulin Watershed in Xingtai City, Hebei Province as the research area, the HEC-HMS hydrological model and the HEC-HMS and HEC-RAS coupling model were constructed, respectively, to simulate 26 flood events during the period from 1982 to 2016. The results indicate that the coupled model can reflect the evolution process of river floods. When simulating certain major flood events, the percentage of flood peak error and Nash–Sutcliffe efficiency coefficient (NSE) have improved, such as the NSE of No. 160812 floods increasing from 0.9 to 0.95. However, the simulation accuracy of these two models for small floods in the watershed is relatively low. Future research should focus on how to accurately evaluate the parameter curve number (CN) of the watershed before rainfall and obtain more accurate runoff yield.

An Improved Xin’anjiang Hydrological Model for Flood Simulation Coupling Snowmelt Runoff Module in Northwestern China

The Xin’anjiang hydrological model (XHM) is the practical tool for runoff simulation and flood forecasting in most regions in China, but it still presents some challenges when applied to Northwest China, where the river runoff mostly comes from high-temperature snowmelt, as the model lacks such a functional module. In this study, the improved XHM coupling snowmelt module is presented to complete the existing XHM for better suitability for flood simulation in areas dominated by snowmelt. The improved model includes four sub-models: evapotranspiration, runoff yield, runoff separation, and runoff routing, where the snowmelt runoff module is introduced in both the runoff yield and separation sub-models. The watershed is divided into two types, non-snow areas with lower altitudes and snow-covered areas with higher altitudes, to study the mechanism of runoff production and separation. The evaluation index, determination coefficients (R2), mean square error (MSE), and Nash efficiency coefficients (NSE) are used to assess the improved XHM’s effect by comparing it with the traditional model. Results show that the R2 of the improved XHM coupled with snowmelt are around 0.7 and 0.8 at the Zamashk and Yingluoxia stations, respectively, while the MSE and NSE are also under 0.4 and above 0.6, respectively. The absolute value of error of both flood peaks in the Yingluoxia station simulated by improved XHM is only 10% and 6%, and that of traditional XHM is 32% and 40%, indicating that the peak flow and flood process can be well simulated and showing that the improved XHM coupled with snowmelt constructed in this paper can be applied to the flood forecasting of the Heihe River Basin. The critical temperature of snow melting and degree-day factor of snow are more sensitive compared with other parameters related to snow melting, and the increasing trend of peak flow caused by both decreased critical temperature and increased degree-day factor occurs only when the value of the model’s state (snow reserve) is higher. These results can expand the application scope in snow-dominated areas of the XHM, providing certain technical references for flood forecasting and early warning of other snowmelt-dominated river basins.

Effects of Soil–Rock Geomorphic Units on the Yield of Surface Runoff: A Case Study on Uncultivated Land of a Karst Area

Surface runoff on karst is a multifactorial hydrological process. There are a great number of studies focusing on rainfall–runoff from karst slopes on a large scale, but microscale studies related to soil–rock geomorphic units have been rarely reported. This study used rock–soil runoff plots on uncultivated land as a new form of natural rainfall catchment, and the yield of surface runoff was measured during four different rainfall events. Through monitoring rainfall runoff by soil–rock runoff plots under different rainfall events, it has been proven that the coefficient of surface runoff measured on uncultivated land of a karst area is very small compared to that of non-karst areas, only ranging from 0.0145 to 0.0408 in the measurement period. And multiple regression analysis showed that the rocks contributed less to the yield of surface runoff than the soils, and with the increase in rainfall, the contributions of both showed an increasing trend. The calculated surface runoff yield produced by soils showed a positive relationship with soil bulk density and a negative relationship with soil porosity, soil hydraulic conductivity, and root biomass, and the significance increased with rainfall, which was consistent with previous findings and demonstrated the accuracy and efficiency of the proposed method in our study. These study results contribute to a deeper understanding of the rainfall–runoff process in rocky desertification areas, and the proposed method of soil–rock runoff plots provides a new way to estimate the yield of rainfall runoff on the complicated geomorphic units of karst slopes.

Surface runoff and soil erosion from Nitisols and Ferralsols as influenced by different soil organic carbon levels under simulated rainfall conditions

Soil erosion poses a challenge to the environment and the sustainable use of natural resources, particularly in relation to agricultural production. The study aimed to assess the influence of different soil organic carbon (SOC) levels on runoff and soil erosion under varying levels of rainfall intensity. The study was conducted in pre-selected farmers' fields representing low, moderate and adequate SOC levels in Nitisols and Ferralsols. Two parallel experiments were set up in each type of soil using a split-plot layout arranged in Randomized Complete Block Design. The main plots were the different soil organic carbon levels while the sub-plots were the different simulated rainfall intensities. Rainfall simulation was then conducted to determine runoff and sediment losses on each soil type. The simulation was done using a land type sprinkler nozzle rainfall simulator (460 788 type) in an experimental plot of 1 m2, fenced with corrugated iron sheets with a small opening left for runoff collection. Runoff and sediment losses were determined from the volume collected in the jar. The data was subjected to analysis of variance and significant mean differences were determined using Tukey’s Honest Test at a 95% confidence level. Pearson correlation was applied to assess the relationship between runoff volume and sediment loss. The results showed that Ferralsols recorded significantly higher runoff and sediment losses compared to Nitisols, by 60.27% and 53.14% respectively. However, adequate SOC level portrayed a significant effect in reducing erosion in both soil types, where it reduced runoff and sediment loss by 45.30% and 48.38% in Ferralsols and by 65.31% and 48.22% in Nitisols, respectively. In both soil types, runoff yield was positively correlated to rainfall intensity while sediment yield was inversely correlated with SOC levels. Therefore, the study recommends incorporation of organic matter to adequate levels in both soils, for reduced soil erosion.

Particularity of hydrological processes under heavy ablation based on environmental isotopes in transition zones between endorheic and exorheic basins

Drastic changes in the cryosphere have a significant impact on the quantity and formation process of water resources in the Qilian Mountains. The present study focused on quantitative evaluation of runoff components and runoff formation processes during strong ablation periods (August), in 2018, 2020, and 2021, in the transition zone between endorheic and exorheic basins in China, based on 1906 stable isotope samples. The results revealed that as the altitude decreased, the contribution of glacier and snow meltwater and permafrost water to runoff decreased, whereas that of the precipitation increased. Precipitation is a major source of river runoff in the Qilian Mountains. Notably, the runoff yield and concentration of rivers that were greatly affected by the cryosphere exhibited the following characteristics: (1) The altitude effect of stable isotopes was not significant and even showed a reverse trend in some rivers. (2) The processes of runoff yield and composition were relatively slow; as such, precipitation, glacier and snow meltwater, and supra-permafrost water were first transformed into groundwater and then supplied runoff to upstream mountainous region. (3) Finally, stable isotope composition in such rivers were similar to those in glaciers and snow meltwater, with small fluctuations. Therefore, the water sources of rivers affected by the cryosphere are more uncertain than those of rivers unaffected by the cryosphere. In future study, a prediction model of extreme precipitation and hydrological events will be developed, and a prediction technology for runoff formation and evolution in glacier snow and permafrost will be developed to integrate short-and long-term forecasts.

Multi-temporal spatial modelling to assess runoff and sediment dynamics under different microtopographic patterns

Soil erosion is a multi-scale geographical interface process with high spatiotemporal variability. This study aimed to assess runoff and sediment dynamics under different microtopographic patterns based on wavelet analysis and SIMulated Water Erosion model (SIMWE). Three rainfall intensities of 1.0 mm min−1, 1.5 mm min−1, and 2.0 mm min−1, combined with three slope gradients of 10°, 15°, and 20°, were utilized to conduct rainfall simulations on three soil boxes measuring 4 m in length and 0.8 m in width. The soil boxes exhibited distinct microtopographic patterns, including smooth slope (CK), artificial digging (AD), and ridge tillage (RT). The results showed that the runoff and sediment reduction benefits of different tilled slopes decreased with an increase in both slope and rainfall intensity. The AD and RT slopes reduced runoff yields by 8.4% − 50.2% and 17.3% − 75.0% respectively compared to CK slope. Although sediment yields from AD and RT slopes were reduced by 4.2% − 51.6% and 1.8% − 53.0%, respectively, the sediment control benefits of AD and RT slopes were basically lost when the slope gradient increased to 20°. The rill erosion was the main source of soil erosion on different tilled slopes, accounting for 72% − 87% of the total soil loss. And the rates of both soil erosion and rill erosion exhibited a power function relationship with an increase in rainfall intensity and slope. The impact of slope gradient on soil erosion on the RT slope was greater than those on the CK and AD slopes. During the development of rill erosion, non-stationary and multi-scale periodic phenomena exist in the time series of runoff and sediment on different microreliefs. As surface microrelief increased, the fluctuations in runoff and sediment on tilled slopes intensified, resulting in a gradual shortening of the variation period. And this study verified the feasibility of the SIMWE model to simulate the runoff and sediment dynamics on microtopographic scale under a single rainfall event. The results can provide a theoretical basis for the scientific layout of soil and water conservation practices in sloping farmland and the construction of soil erosion model in purple soil area.