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Climate change and human activities exert significant influence on the water–sediment relationship in arid and semi-arid regions. Therefore, comprehending the underlying mechanisms is crucial for the effective management of water and soil resources, as well as integrated watershed management. This research focuses on the Kuye River watershed (KYH_W) in the middle reaches of the Yellow River in China, along with its sub-watersheds Wangdaohengtazi (WDHT_SW) and Xinmiaosi (XM_SW). This paper utilizes the Mann–Kendall non-parametric test and the double cumulative curve method to examine the interannual trends of runoff, sediment transport, precipitation, temperature, and NDVI factors. Furthermore, the method of the slope change ratio of cumulative quantity (SCRCQ) is utilized to quantitatively evaluate the impacts and contribution rates of climate change and human activities on water–sediment changes within each watershed. The results are as follows: (1) From 1969 to 2019, the entire watershed experienced a significant decrease in both runoff and sediment transport, with 1997 marking the year of abrupt change. However, following 2012, the KYH_W and WDHT_SW exhibited a noticeable rebound in runoff. (2) Human activities predominantly contribute to the reduction in water and sediment in the watershed. (3) After the abrupt change, between 1998 and 2011, the contribution rates of climate change and human activities to the annual runoff reduction in the entire KYH_W reached 33% and 64%, respectively. Moreover, these rates for sediment transport reduction reached 26% and 74%, respectively. Subsequently, after 2012, the contribution rates of both factors to the increase in watershed runoff reached 29% and 71%, respectively. Factors other than the NDVI, within human activities, played a dominant role in augmenting the watershed's runoff. (4) Prior to 2011, changes in vegetation cover resulting from the Grain for Green Program, as measured by the NDVI, emerged as the primary factor responsible for reduced runoff in the watershed. Conversely, factors other than the NDVI assumed dominance in reducing sediment transport. The SCRCQ method offers a quantitative approach to assessing water–sediment changes. Based on this method, the study further underscores the substantial impacts of climate change and human activities on variations in runoff and sediment transport within the KYH_W in the middle reaches of the Yellow River. Notably, the water–sediment changes in the KYH_W exhibit distinct stage-wise and spatial discrepancies, which warrant increased attention in future research endeavors. [ABSTRACT FROM AUTHOR]

Both vegetation coverage rates and arrangement patterns have important influences on erosion. Very little previous research focuses on the impacts of spatial vegetation distribution patterns on erosion. The slope-gully system was taken as the research object, which is composed of a 5.0 m long hillslope with a slope gradient of 20° and a 3.0 m long gully slope with a gradient of 50°. A series of scouring experiments with two inflow discharges (3.2 L min−1, 5.2 L min−1) was carried out. The effects of the flow discharges, spatial grass arrangement patterns (US, MS, and DS represent the presence of grass covering on up-hillslope, middle-hillslope, and down-hillslope, respectively) and grass coverage rates (0%, 30%, 50%, 70%, and 90%) on runoff and sediment were studied in this paper. The results indicated that either runoff or sediment yielding was significantly decreased with the grass coverage rates increasing and with the variation of grass arrangement patterns on a hillslope. While grass coverage had more effectiveness in controlling erosion compared with runoff reduction, and DS can control erosion more effectively than US and MS erosion controlling. For the gully slope, erosion significantly increased with the grass coverage rates increasing no matter how the grass arrangement patterns on the hillslope. Therefore, both different grass coverage and different grass arrangement patterns have an influence on erosion processes; any research that only takes care of the single factor mentioned above is not enough to reveal the effects of grass on erosion. In the process of erosion control in the Loess Plateau, taking effective measures both on the hillslope and gully slope will be effective methods of reducing soil erosion. [ABSTRACT FROM AUTHOR]

The Yellow River is the mother river of the Chinese nation. The source region of the Yellow River is an important region for water conservation in China. The hydro-ecological environment of the Yellow River source region is very fragile. Therefore, the variation processes of runoff and sediment discharge in the Yellow River source region have become the subject of considerable concern in recent years. However, the source region of the Yellow River has been studied relatively little, and the influence of these two process in the source region of the Yellow River remains unclear. In this paper, precipitation, runoff, sediment discharge, and their interactions in the source region of the Yellow River from 1956 to 2018 were analyzed using several different time-series evaluation methods, such as Spearman's rank correlation coefficient method, the ordered clustering analysis method, and the double-mass curve method. Furthermore, the impact of Huangheyuan hydropower station on these hydrological elements was analyzed in relation to the few other human activities in Sanjiangyuan National Nature Reserve. The results indicated that the precipitation in the source region of the Yellow River increased significantly, the sediment discharge decreased non-significantly, and there was no significant change in runoff over this time period. The years 1995 and 2011 were probable mutation points of the sediment discharge series, and the mutation point of the precipitation series was likely 2001. The Huangheyuan hydropower station is the main reason for the decrease in annual sediment discharge in the source region of the Yellow River. [ABSTRACT FROM AUTHOR]

Multivariate hydrological series become nonstationary under the changing environment. In this paper, a new method is proposed to study the change in the dependence structure between runoff and sediment sequences. First, a moving cut transfer entropy is proposed to detect the sudden change point in the dependence structure between runoff and sediment. Then, the Gumbel copula with a new parameter estimation method (MEE) is employed to construct the dependence structure of runoff and sediment before or after the change point for situation with small samples. The new method is applied to the annual runoff and sediment discharge series in Xiliugou River, China. It is found that the dependence structure between runoff and sediment changed abruptly in 2000. The joint probabilistic characteristics of the annual runoff and sediment discharge during the period of 1960–1999 are built based on the values of RMSEs and AICs. The joint distribution of the annual runoff and sediment discharge during the period of 2000–2016 is constructed by the Gumbel copula with MEE. Moreover, the synchronous encounter probability of runoff and sediment decreases from 0.76 to 0.63, and the asynchronous encounter probability rises from 0.24 to 0.37, after the runoff and sediment discharge series presents a significant change in the dependence structure. [ABSTRACT FROM AUTHOR]

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Investigating the changes in the runoff and sediment coupling relationship in the Middle Yellow River Basin of China can not only deepen the understanding of soil loss control in arid areas, but also help solve key issues of regional ecological protection. Since the 1960s, soil- and water-conservation projects have been implemented in the Middle Yellow River Basin, inducing a significant reduction in runoff and sediment and changes in the relationship between runoff and sediment. The study identified the change points of coupling relationship between runoff and sediment in the Wuding River Basin (WRB) by constructing a diagnostic method based on coupling coordination degree and the Pettitt test; the study validated this using the Copula function and analyzed the impacts of erosion energy and underlying surface factors. The results showed the following: (1) the method based on coupling coordination degree and the Pettit test could accurately reflect the coupling relationship of runoff and sediment and identify two change points (1971 and 1996); (2) runoff and sediment in the WRB decreased gradually over three periods (P1, 1960–1970; P2, 1971–1995; P3, 1996–2020), with an average annual runoff of 15.34 × 108, 10.72 × 108, and 8.32 × 108 m3 and average annual sediment load of 1.84 × 108, 0.82 × 108, and 0.32 × 108 t, respectively; (3) the maximum possible joint design value of runoff and sediment under different return periods in P1 were all the highest, followed by P2 and P3, and the larger the return period, the higher the maximum possible joint design value; (4) runoff erosion power could promote runoff and sediment in PE (1960–2020), P1, P2 and P3 at a significant level, check dams and terrace could decrease runoff and sediment significantly in PE, and the highest contribution to runoff reduction was check dam (95.4%), while the highest contribution to sediment reduction was REP (93.8%). The study can provide a new way to analyze the changes in the runoff and sediment relationship and provide scientific support for runoff and sediment regulation in the Middle Yellow River Basin. [ABSTRACT FROM AUTHOR]

• Calculation unit division induced soil spatial aggregation in SWAT model. • Effect of soil spatial aggregation on simulation was separated and quantified.Soil spatial aggregation caused a significant increase in annual runoff and sediment load. • The effect of soil spatial aggregation on sediment load was greater than on runoff. • Optimal sub-watershed division scheme was discussed. Distributed hydrological model divides watersheds into distinct calculation units to simulate hydrological processes. Within the model, different calculation unit division schemes induce input elements, such as soil and land use, to certain degrees of generalization, thus affecting the simulation result. Analyzing the effect of the calculation unit division on the simulation result is an important methodology to reduce uncertainty and improve the simulation accuracy of the model. Previous researchers have focused on the comprehensive effect of underlying surface generalization (such as soil, land use, and terrain generalization) caused by the calculation unit division on the simulation results, while it did not separate the effect of the generalization of the individual input factor on the simulation result. In this paper, the Dongjiang headwater region in southern China was selected as the study area. The single type of land use and slope were input into the Soil and Water Assessment Tool (SWAT) model to fix the effects of land use and terrain caused by calculation unit division on the simulation results. Eleven calculation unit division schemes were used to analyze the impact of soil spatial aggregation on runoff and sediment load simulations. The calculation unit division schemes included 11 sub-watershed division schemes and their hydrological response unit (HRU) thresholds were set at 8 %. The drainage area thresholds of the 11 sub-watershed division schemes were 30 ha, 60 ha, 120 ha, 240 ha, 480 ha, 1000 ha, 1600 ha, 2200 ha, 2800 ha, 3400 ha and 4000 ha. The results demonstrated that the soil spatial distribution showed an obvious aggregation with an increase in the drainage area threshold in the SWAT model. Of these, the Krasnozem soil type which covers the largest area in the watershed, increased significantly with an increase in the drainage area threshold. However, the areas of all the other soil types decreased significantly. The Lioth soil type covers the smallest area in the watershed decreased and even disappeared when the threshold in the SWAT model was greater than 1000 ha. Furthermore, soil spatial aggregation caused a significant increase in the annual runoff and sediment load (P < 0.05), with the sediment load (Re = 29.78 %) increasing at a greater rate compared to runoff (Re = 1.74 %). Increased soil aggregation significantly increased the sediment loads in the maximum 1-day, the continuous maximum 5-day, the continuous maximum 7-day, and the sediment load in flood processes (P < 0.001). Refining the calculation unit division scheme will cause a significant increase in the number of calculation units. Due to the computer processing power limitations, we cannot further refine the calculation unit division scheme. Based on our current operational calculation unit division scheme, we did not identify the optimal division scheme in the study region. These results can provide reference information for future research into hydrological model uncertainty and can improve the SWAT model simulation accuracy. [ABSTRACT FROM AUTHOR]

The main goal of this study was to evaluate the performance of AnnAGNPS (Annualized AGricultural NonPoint Source) pollution model, in calculating runoff, sediment loading and nutrient loadings for Funiu Mountain area. Most of the model input parameters were sourced from Luanchuan Forest Ecology Station (LFES) in Funiu Mountain area. The data on 23 storms in 2018 was used to calibrate the model and the data on 33 storms in 2019 for validation. The whole evaluation consisted of determining the coefficient of determination (R²), Nash-Sutcliffe coefficient of efficiency (E), and the percentage volume error (VE). Results showed that the runoff volumes were underpredicted by 5.0% with R² of 0.93 (P<0.05) during calibration and underpredicted by 5.3% with R² of 0.90 (P < 0.05) during validation. But sediment loading was able to produce a moderate result. The model underpredicted the daily sediment loading by 15.1% with R² of 0.63 (P < 0.05) during calibration and 13.5% with R² of 0.66 (P < 0.05) during validation. Nitrogen loading was overpredicted by 20.3% with R² = 0.68 (P < 0.05), and phosphorus loading performance was slightly poor with R2 = 0.65 ( P < 0.05) during validation. In general, the model performed well in simulating runoff compared to sediment loading and nutrient loadings. [ABSTRACT FROM AUTHOR]

Exploring the relationship between runoff and sediment elements in a river basin is a prerequisite for realizing the scientific management scheme of runoff and sediment. In this study, six commonly applied probability distributions are utilized to fit the marginal distribution, and three Archimedes copulas are used to fit the joint distribution to build a joint probability distribution model of river runoff and sediment in sandy areas. The synchronous and asynchronous encounter probabilities of runoff and sediment are calculated. The uncertainties of marginal distribution, parameter estimation, and copula function in the process of constructing the joint distribution model framework are analyzed. The results indicate that: (1) The runoff and sediment series from 1954 to 2015 of the Huangfuchuan River basin are divided into three stages by using the cumulative anomaly method and the double mass curve method, and the runoff and sediment in the three stages have strong correlations. In the  T a  (1954–1978) and  T b  (1979–1996) stages, the optimal joint distribution functions of runoff and sediment are Gumbel, and in the  T c  (1997–2015) stage the optimal joint distribution function is Clayton; (2) The synchronous probabilities of runoff and sediment series in the three stages are 69.84%, 84.82%, and 70.72%, respectively, which are much greater than the asynchronous frequencies of abundance and depletion, and this showed that the conditions of runoff and sediment in the river basin are consistent; (3) The joint distribution function is sensitive to the choice of marginal distributions, parameters, and copula functions, and the optimal marginal distribution function, optimal copula function, and the parameters selected by the maximum likelihood estimation method can better fit the runoff-sediment relationship in the river basin and reduce the process uncertainty. [ABSTRACT FROM AUTHOR]

Summary Land cover and rainfall regime are two important factors that affect soil erosion. In this paper, three land cover types – grass cover, litter cover and bare land – were employed to analyze surface runoff, subsurface flow and sediment loss processes in relation to the rainfall regimes in the red soil region of China. Five rainfall regimes were classified according to 393 rainfall events via a k-means clustering method based on the rainfall depth, duration and maximum 30-min intensity. The highest surface runoff coefficient and erosion amount were found on bare land in all five rainfall regimes, and the lowest were found on grass cover. The litter cover generated the highest subsurface flow rate, followed by the grass cover; the lowest was on bare land. For grass cover and litter cover plots, rainfall events of rainfall regime IV which had the longest duration, greatest depth and lowest intensity had the highest surface runoff coefficient, soil erosion amount and subsurface flow rate. For bare land, storm rainfall events of rainfall regime V had the highest intensity, lowest depth and duration, had the highest surface runoff coefficient and soil erosion amount, but the lowest subsurface flow rate. The highest subsurface flow rate of bare land happened in rainfall regime IV. Surface cover was urgently needed to reduce soil erosion. When the lands under dense surface cover, more attention should be paid to rainfall events that of long duration, high depth but low in intensity which commonly occurred in spring. The interactions of surface–subsurface flow and its effects on soil erosion and nutrient loss were worth considering in the red soil region. [ABSTRACT FROM AUTHOR]

Soil erosion changes after China's Grain‐for‐Green Program (GGP) have attracted widespread attention. Many studies have reported positive contributions of the GGP to sediment reduction; however, GGP effects on runoff remain under debate. The objective of this study was to identify runoff and sediment changes and estimate the contribution of human activities to soil erosion decreases in the Mang River basin (MRB) in the southeastern Loess Plateau. The temporal trends of the rainfall‐runoff‐sediment series between 1960 and 2017 and the contribution of human effects to runoff and sediment changes were determined using time‐series analysis methods. The main transformations in land‐use types were from farmland to forestland in the upstream MRB and farmland to built‐up land in the downstream MRB. Rainfall remained in a relatively steady state, while runoff and sediment had descending trends, both of which began to mutate in 1990 and 1994, respectively. The average runoff (sediment load) decreased by 33 × 104 m3 (5 × 104 t yr−1), of which the human effect contributed to 79% (93%) of the decreases. During the descending period, the human effects on runoff and sediment increased with time. Sediment experienced a much larger reduction effect than runoff because of increased forestland area, which can greatly reduce soil erosion, in the MRB upstream of our study site; however, runoff was increased in the MRB downstream of our study site because urbanization led to the expansion of impervious surfaces. Our results provide new lessons for assessing the reduction effects of the GGP on soil erosion in an urbanized basin. [ABSTRACT FROM AUTHOR]

Soil erosion has become more serious in semiarid areas around the world. However, the discrimination of the impact of concurrent climate change and human activity on soil erosion in a particular study area remains a challenge. Check dams are important engineering measures to prevent soil erosion on the Chinese Loess Plateau, and the dam sediments, as the product of soil erosion, are related to both climate change and human activities in a small watershed. The present study selected a check dams sediment profile in the upper Jinghe Basin on the Chinese Loess Plateau as a case study. Based on AMS 14C dating and 137Cs measurement, we established the soil erosion timescale and employed multiple methods including magnetic susceptibility, particle size, and minerals to trace the soil erosion history. We compared them with a local hydrometeorological record in the Jinghe Basin to explore the relationship between soil erosion and human activities. AMS 14C and 137Cs results indicated that the profile was deposited since 1953. The results of magnetic susceptibility, particle size, and minerals revealed 3 soil erosion phases during the last 60 years. Soil erosion in this region is not only related to precipitation changes, but also closely related to human activities. Prior to the Reform and Opening-up in China in 1978, climatic change played a leading role in check dams sedimentation and hydrological changes. Subsequently, despite accelerated soil erosion associated with the family contract responsibility system, the check dams, afforestation and a warmer climate mitigated the soil erosion to some extent, runoff and sediment load continued to decrease. Since 1999, China's Grain for Green project has greatly reduced the runoff and sediment load. However, the policy of filling gullies and creating land since 2010 should be reconsidered carefully in terms of all aspects, including the eco-environment, hydrological cycle, and economics. [ABSTRACT FROM AUTHOR]

Abstract: Vegetation recolonization has often been used to control roadside slope erosion, and in this paper, four restoration models – Natural Restoration, Grass, Grass & Shrub, Sodded Strip – were chosen to recolonize the plants on a newly built unpaved roadside slope in the Three Gorges Reservoir Area. After eight months growth, eight rainfall simulations (intensity of 90mmh−1 for 60min) and in-situ soil shear strength test were then carried out to identify the impacts of vegetation on roadside slope erosion and soil shear strength. The erosion on cutslopes was higher than that on fillslopes. The runoff coefficient and soil detachment rate were significantly lower on the Grass & Shrub model (4.3% and 1.99gm−2 min−1, respectively) compared with the other three, which had the highest surface cover (91.4%), aboveground biomass (1.44kgm−2) and root weight density (3.94kgm−3). The runoff coefficient and soil detachment rate on roadside slopes showed a logarithmic decrease with the root weight density, root length density and aboveground biomass. The soil shear strength measured before and after the rainfall was higher on Grass & Shrub (59.29 and 53.73kPa) and decreased on Grass (46.93 and 40.48kPa), Sodded Strip (31.20 and 18.87kPa) and Natural Restoration (25.31 and 9.36kPa). Negative linear correlations were found between the soil shear strength reduction and aboveground biomass, root weight density and root length density. The variation of soil shear strength reduction was closely related to the roadside slope erosion, a positive linear correlation was found between runoff coefficient and soil shear strength reduction, and a power function was shown between soil detachment rate and soil shear strength reduction. This study demonstrated that Grass and Grass & Shrub were more suitable and highly cost-effective in controlling initial period erosion of newly built low-volume unpaved road. [Copyright &y& Elsevier]

Runoff and sediment discharge have displayed great reductions due to climate change and enhanced various human activities during recent decades in the Jialing River, China, with significant environmental and social implications. The water balance equation, double mass curve, and linear regression analysis were employed to quantify the contributions of climate change and human activities to runoff and sediment discharge reductions in the Jialing River during 1960–2017. The results indicated that the annual runoff of the Jialing River exhibited a significant decreasing trend of − 2.75 × 108 m3 every year (P < 0.05) but no significant abrupt change occurred, while annual sediment discharge significantly decreased by 0.03 × 108 t every year (P < 0.05) with a significant abrupt change in 1990 (P < 0.05). Climate change led to a great reduction (82.2%) in annual runoff from 1960 to 2017 in the Jialing River, whereas the contribution of climate change to sediment discharge reduction in the human-affected period (1990–2017) was only 4.55% and precipitation inclined to increase sediment discharge in recent years (2010–2017). The reduced sediment discharge in the 1990s was mostly due to the implementation of soil–water conservation programs and the reduction after 2000 was due to the development of reservoirs as well as the implementation of soil–water conservation programs. The results provided references to develop various human activities better and drew great attention to strengthening basin management. [ABSTRACT FROM AUTHOR]

Investigation of the variations in runoff, sediment load, and their dynamic relation is conducive to understanding hydrological regime changes and supporting channel regulation and fluvial management. This study is undertaken in the Xihanshui catchment, which is known for its high sediment‐laden in the Jialing River of the Yangtze River basin, southern China, to evaluate the change characteristics of runoff, sediment load, and their relationship at multi‐temporal scales from 1966 to 2016. The results showed that runoff changed significantly for more months, whereas the significant changes in monthly sediment load occurred from April to September. The contributions of runoff in summer and autumn and sediment load in summer to their annual value changes were greater. Annual runoff and sediment load in the Xihanshui catchment both exhibited significant decreasing trends (p < 0.05) with a significant mutation in 1993 (p < 0.05). The average annual runoff in the change period (1994–2016) decreased by 49.58% and annual sediment load displayed a substantial decline with a reduction of 77.77% in comparison with the reference period (1966–1993) due to climate change and intensive human activity. The power functions were satisfactory to describe annual and extreme monthly runoff–sediment relationships, whereas the monthly runoff–sediment relationship and extreme monthly sediment‐runoff relationship were changeable. Spatially, annual runoff–sediment relationship alteration could be partly attributed to sediment load changes in the upstream area and runoff variations in the downstream region. Three quantitative methods revealed that the main driver for significant reductions of annual runoff and sediment load is the human activity dominated by soil and water conservation measures, while climate change only contributed 22.73%–38.99% (mean 32.07%) to the total runoff reduction and 3.39%–35.56% (mean 17.32%) to the total decrease in sediment load. [ABSTRACT FROM AUTHOR]

Purpose: Significant changes in the runoff and sediment load have been detected in many catchments of the Loess Plateau. These changes are expected to be influenced by the interplay of climate variability and human activities. Quantitatively evaluating these effects is crucial for framing climate variability adaptation measures and the assessment and management of regional water resources. Materials and methods: Based on the annual rainfall, runoff, and sediment load data taken over the period from 1974 to 2013 and using data from 112 flood events, this study investigates the runoff and sediment load variations at the annual scale and distinguishes the impacts of climate variability and human activities at the event scale. The Mann-Kendall test and Pettitt's test are employed to detect the trends and abrupt change points of the annual runoff and sediment load. Rainfall and land surface conditions play a dominant role in the runoff and sediment yield of flood events. However, vegetation recovery, which benefits from the Grain-for-Green project and the construction of check dams has greatly changed the land surface condition, resulting in a reduction in streamflow energy, hydrological connectivity, and flood peaks. Therefore, for two flood events with similar rainfall conditions but different runoff and sediment yield, the differences in the runoff and sediment load within paired events may be attributed to the changes in the land surface condition induced by human activities. Results and discussion: The results showed that the annual runoff and sediment load has significantly decreasing trends (p < 0.05). The abrupt changing point was detected in 1996, dividing the runoff and sediment load series into a baseline period (1974–1995) and a changing period (1996–2013). At the flood event scale, the hysteresis analysis showed that the counter-clockwise and figure-eight loops are the main patterns for both of the periods. The relationships between the runoff depth (H) and sediment yield (SY) varied greatly in 2007–2013 compared with those during 1974–1989. Human activities accounted for an average of 47 and 81% for the changes in the runoff and sediment load, respectively, and the remainder was attributable to climate variability. Conclusions: Human activities have a greater effect on the sediment load reduction in the Xichuan River catchment, while climate variability accounted for more of the runoff changes. [ABSTRACT FROM AUTHOR]

The Loess Plateau of China has experienced a lengthy drought and severe soil erosion. Changes in precipitation and land use largely determine the dynamics of runoff and sediment yield in this region. Trend and mutation analyses were performed on hydrological data (1981-2012) from the Yanwachuan watershed in the Loess Plateau Gully Region to study the evolution characteristics of runoff and sediment yield. A time-series contrasting method also was used to evaluate the effects of precipitation and soil and water conservation (SWC) on runoff and sediment yield. Annual sediment yield declined markedly from 1981 to 2012 although there was no significant change in annual precipitation and annual runoff. Change points of annual runoff and annual sediment yield occurred in 1996 and 1997, respectively. Compared with that in the baseline period (1981-1996), annual runoff and annual sediment yield in the change period (1997-2012) decreased by 17.0% and 76.0%, respectively, but annual precipitation increased by 6.3%. Runoff decreased in the flood season and normal season, but increased in the dry season, while sediment yield significantly declined in the whole study period. The SWC measures contributed significantly to the reduction of annual runoff (137.9%) and annual sediment yield (135%) and were more important than precipitation. Biological measures (forestland and grassland) accounted for 61.04% of total runoff reduction, while engineering measures (terraces and dams) accounted for 102.84% of total sediment yield reduction. Furthermore, SWC measures had positive ecological effects. This study provides a scientific basis for soil erosion control on the Loess Plateau. [ABSTRACT FROM AUTHOR]

We analyze the variability of sediment discharge and runoff in the Hekou-Longmen segment in the middle reaches of the Yellow River, China. Our analysis is based on Normalized Difference Vegetation Index (NDVI), sediment discharge, runoff, and monthly meteorological data (1961-2010). The climate conditions are controlled via monthly regional average precipitation and potential evapotranspiration (ET) that are calculated with the Penman-Monteith method. Data regarding water and soil conservation infrastructure and their effects were investigated as causal factors of runoff and sediment discharge changes. The results indicated the following conclusions: (1) The sediment concentration, sediment discharge, and annual runoff, varied considerably during the study period and all of these factors exhibited larger coefficients of variation than ET and precipitation. (2) Sediment discharge, annual runoff, and sediment concentration significantly declined over the study period in a linear fashion. This was accompanied by an increase in ET and decline in precipitation that were not significant. (3) Within paired years with similar precipitation and potential evapotranspiration conditions (SPEC), all pairs showed a decline in runoff, sediment discharge, and sediment concentration. (4) Human impacts in this region were markedly high as indicated by NDVI, and soil and water measurements, and especially the soil and water conservation infrastructure resulting in an approximately 312 Mt year of sediment deposition during 1960-1999. [ABSTRACT FROM AUTHOR]

Severe soil erosion in the Loess Plateau region and associated large sediment discharge downstream in China have been of great concern for years. A physically based distributed model, the Digital Yellow River model (DYRIM), was developed in 2007 for land management at the basin scale in this region. In DYRIM, an explicit sediment yield equation was derived based on simple assumptions where sediment discharge would increase nonlinearly with the slope length, leading to unrealistic results as the spatial scale increases. The main aims of this study were to reformulate the module of DYRIM in comparison with other process-based erosion models; to develop a generic framework for erosion prediction and simulation of erosion and sediment delivery processes within storm events; to validate the new hillslope erosion module for improved performance across a range of spatial scales; and to evaluate parameter consistency among different runoff events. Observed flow and sediment discharge data for 16 runoff events and three runoff plots with different slope lengths (20, 40, and 60 m) for each runoff event from the Tuanshangou experimental site in the Loess Plateau region were used to calibrate the new module for a 20 m slope and the calibrated parameter values were then used to predict the sediment discharge for slope lengths of 40 and 60 m at the same site. For calibration, the Nash-Sutcliffe coefficient of efficiency (NSE) was 0.92 on average for the 20 m plot. For prediction, the average NSE values were 0.87 for 40 m plot and 0.90 for the 60 m plot. There is a marked improvement over the existing module, for prediction with the existing module, the average NSE values were only -0.86 for the 40 m plot and -6.3 for the 60 m plot. Whereas the calibrated parameter values vary from event to event, results show that using a common set of parameter values for all runoff events to predict sediment discharge, the overall NSE values using the combined data set are as high as 0.89 for the 40 m plot and 0.90 for the 60 m plot. This research shows that it is absolutely imperative to include a control term involving the sediment transport capacity, even for the highly erodible region of the Loess Plateau in China. [ABSTRACT FROM AUTHOR]

To evaluate the effect of comprehensive management on runoff and sediment reduction in meso-scale watersheds, the Yanwachuan watershed of Loess tableland gully region in China was investigated. Variation trends of the runoff and sediment from 1981 to 2009 were analysed, and the year of abrupt change was identified using the double mass curve method, accumulative departure method, moving t-test method and Yamamoto method. Next, the effects of comprehensive management on runoff and sediment reductions were quantitatively evaluated based on the runoff/sediment coefficient method and double mass curve method, both capable of separating the effect of climate change from that of comprehensive management. Finally, the driving forces of runoff and sediment variations were discussed from both climatic and comprehensive management aspects. The results showed that the runoff and sediment in the watershed had significantly decreased since an abrupt change in 1997. During the change period (1998-2009), the erosive precipitation and precipitation erosivity had been reduced by 32.4% and 17.4%, respectively, compared with the base period (1981-1997); the areas of forest and grass had increased; and the normalized difference vegetation index (NDVI) had increased by 20.6% with significantly enlarged vegetation coverage. The benefit value of runoff reduction and sediment reduction were 27.3% and 76.2%, respectively. The resultant runoff and sediment reductions in the watershed were the synergy of climate change and comprehensive management, with greater than 90% reduction contributed by comprehensive management. All these results supported that comprehensive management played the dominant role in runoff and sediment reductions. [ABSTRACT FROM AUTHOR]

(1) Background: To reveal the intrinsic relationship between the tidal flat sediments in an estuary wetland and the runoff from the upstream river. This research was conducted in the tidal flats of the Liaohe estuary wetland. (2) Methods: The 137Cs and 210Pb dating technique was used to reconstruct the time correspondence between tidal flat sediments and runoff, and the periodic response was explored between the changes in the tidal flat sediments and runoff based on the spectrum analysis method. (3) Results: The average sedimentation rate in the tidal flat was 2.24 cm·year−1 during the past 50 years. The amount of fine sediment particles deposited on the estuary tidal flat was directly related to the amount of sediments transported by the river and inversely proportional to the ability of rivers to transport fine matter. The high frequency reproduction cycle of 14–15 years in the flood season flow and 5–6 years in the annual sediment discharge of the Liaohe River correspond to the high and low frequency reproduction cycles of the median size of sediments in Liaohe estuarine wetland tidal flats. (4) Conclusions: The research clarified the hydrological constraints of the action law between Liaohe River runoff and the estuarine sediments. The periodic response between Liaohe River runoff and the sediment was established. [ABSTRACT FROM AUTHOR]

The research on the impact of rainfall patterns on runoff and sediment yield is still insufficient, especially under natural rainfall conditions. We analyzed the influence of rain peak morphology on runoff and sediment yield based on the data of rainfall, runoff, and sediment in the bare runoff plot of Shixia, a small watershed in the Miyun district of Beijing, from 2007 to 2016. We took 0.4 mm min−1 as the standard of rain peak classification and the peak width, peak number, peak value, peak position and multi-peak continuity as the indexes of rain peak morphology. The results showed that: (1) Peak number, peak value, and peak width were significantly correlated with runoff and sediment yield, while peak position was irrelevant. The order of correlation between rain peak morphology indexes and runoff yield was peak width (0.71) > peak number (0.69) > peak value (0.33) > peak position (0.05). The order of correlation between rain peak morphological indexes and sediment yield was peak width (0.62) > peak value (0.36) > peak number (0.36) > peak position (−0.09). The multi-peak continuity was not correlated with runoff (0.12) and sediment yield (0.45). (2) When the number of rain peaks was greater than one in a single rainfall, the amount of runoff and sediment production increased significantly. (3) For multi-peak rainfall, 90 min was the boundary point of the rain peak interval, and the sediment yield formed by rainfall with a rain peak continuity >1/90 min−1 was significantly larger than the rainfall of ≤1/90 min−1. (4) Covariance analysis showed that the runoff caused by rainfall with a peak at the middle positions was obviously more than rainfall with a peak at the front position. However, the peak position had no significant effect on the sediment yield. (5) The peak rainfall amount of a rainfall (TPR) was a comprehensive index reflecting peak number, peak value and peak width, and the correlation between it and the sediment yield and runoff reached 0.60 and 0.71, respectively. Statistical rainfall characteristic indexes included rainfall amount, average rainfall intensity, rainfall duration, I5 (maximum 5-min rainfall intensity), I10, I15, I20, I30, and I60, among which I60 had the strongest correlation with runoff and sediment yield (0.69, 0.60), which were much larger than other rainfall indexes (0.08~0.47, 0.14~0.48) except rainfall amount (0.75, 0.37). By establishing a regression equation, it was found that both TPR and I60 had good explanatory power for runoff and weak explanatory power for sediment yield. [ABSTRACT FROM AUTHOR]