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Water conservation is an important ecosystem service, which is crucial to the fragile ecological environment and serious soil erosion in Northwest China. However, water conservation has been affected by climate change and human disturbance, and its future spatial and temporal changes are still unclear. This study employed the Integrated Valuation of Ecosystem Services and Trade‐offs (InVEST) model to assess the water conservation capacity of Northwest China between 1990 and 2020. Subsequently, the Patch‐generating Land Use Simulation (PLUS) model and the NASA Earth Exchange Global Daily Downscaled Projections (NEX‐GDDP‐CMIP6) were integrated to examine changes in water conservation from 2030 to 2050. The water conservation quantity in Northwest China had a fluctuating growth tendency between 1990 and 2020, with an average of 816.61 × 108 m3. The water conservation capacity's regional distribution pattern shows a steady increase from northwest to southeast. Northwest China's forest land had the greatest water conservation capacity between 1990 and 2020, at 66 mm, while the water land had the lowest, at 1.46 mm. The water conservation capacity in the 2030–2050 future scenario is less than that in 2020 when the regional distribution pattern is comparable to 2020. Natural development scenario (ND) in 2030 has the lowest water conservation capacity (13.41 mm) under ssp1‐2.6 precipitation scenario, whereas in 2050, the highest water conservation capacity (17.47 mm) is found in same scenario. The ecological protection scenario (EP) has the greatest water retention capacity (18.15 mm in 2040) and the lowest (14.38 mm in 2050) in the ssp5‐8.5 scenario. Our research can help restore and rebuild Northwest China's natural ecosystem and offer a theoretical foundation for the protection of ecological environment and the rational utilization of water resources in the region. [ABSTRACT FROM AUTHOR]

Literature studies have found that caregivers play a vital role in children's outdoor play activities. In view of the limitations and the low level of outdoor play (OP) of children in Chinese cities, the present study attempted to reveal the constraints of caregivers on children's OP based on the leisure constraints theory. Through two on-site questionnaire surveys distributed in Hefei, Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA) were used to explore the constraint dimensions of caregivers on children's outdoor play (COP) and to test the adaptability of each in the leisure constraints theory. The study also evaluated the moderating effect of demographic, behavioral and preference variables in using public open spaces on these constraint dimensions. Results showed that: (1) There was a four-dimensional leisure constraint structure for caregivers' constraints on COP, namely "intra-personal," "inter-personal," "structure" and "safety;" (2) Demographics (e.g. age of caregiver, relationship with children, family structure, career, monthly income, etc.), behavioral and preference (e.g. type of site, ways of travel, frequency of visit, etc.) variables of the respondents showed significant differences in these four constraint dimensions. [ABSTRACT FROM AUTHOR]

Over the past three decades, there has been a significant global climate change characterized by an increase in the intensity and frequency of extreme climate events. The vegetation status in Qinghai Province has undergone substantial changes, which are more pronounced than other regions in the Qinghai-Tibet Plateau. However, a clear understanding of the response characteristics of plateau vegetation to extreme climate events is currently lacking. In this study, we investigated the response of net primary productivity (NPP) to different forms of extreme climate events across regions characterized by varying levels of aridity and elevation gradients. Specifically, we observed a significant increase in NPP in relatively arid regions. Our findings indicate that, in relatively arid regions, single episodes of high-intensity precipitation have a pronounced positive effect (higher correlation) on NPP. Furthermore, in high-elevation regions (4000–6000 m), both the intensity and frequency of precipitation events are crucial factors for the increase in regional NPP. However, continuous precipitation can have significant negative impacts on certain areas within relatively wet regions. Regarding temperature, a reduction in the number of frost days within a year has been shown to lead to a significant increase in NPP in arid regions. This reduction allows vegetation growth rate to increase in regions where it was limited by low temperatures. Vegetation conditions in drought-poor regions are expected to continue to improve as extreme precipitation intensifies and extreme low-temperature events decrease. [ABSTRACT FROM AUTHOR]

A new single-site monthly streamflow simulation method that combines the maximum entropy and mixed copula methods is proposed. In this method, the marginal distribution of monthly streamflow is estimated using the maximum entropy theory; this is achieved by the conjugate gradient method of superlinear convergence and low computational expense. Then, a mixed copula is used for the construction of joint distributions of the adjacent monthly streamflow. The developed method is applied to four stations of the Weihe River, China; the results show that the important statistical characteristics of monthly streamflow can be maintained by the entropy-based marginal distribution and that the complex linear and nonlinear dependence between adjacent monthly streamflow can be reproduced by the mixed copula method. Compared with the traditional marginal distribution and the individual copula joint distribution, the entropy-mixed copula method has obvious advantages in goodness-of-fit statistical tests on the marginal and joint distributions. Accurately understanding the monthly runoff distribution is beneficial for flood control during the flood season and solving water shortage problems during the dry season. First, the marginal probability distribution function of each month is established through the principle of maximum entropy. Then, a mixed copula model is used to construct a joint distribution of adjacent monthly runoff. Finally, Gibbs sampling is used to obtain the randomly simulated runoff for each month. The advantage of this method is that it does not require assuming the probability distribution of the runoff series but rather uses important statistical features of the historical series as constraints for deriving the marginal distribution. Accurately describing the complex relationship between water flow sequences, maintaining the statistical characteristics of observation sequences, and improving simulation accuracy are of great significance for water resource planning and management. [ABSTRACT FROM AUTHOR]

Sediment load of China's Yellow River has dramatically decreased due to the interplay of climate variability and human activities in the past decades. However, the contribution of individual driving factors and the detailed spatial distribution of sediment load at a catchment scale were not well understood. In the study, we quantitatively assessed the relative contributions of individual climatic (i.e. precipitation) and anthropogenic (i.e. vegetation restoration, terrace construction) driving factors to sediment load variations in the largest tributary of the Yellow River, Weihe River. The employed annual sediment load measurements and rainfall data for 1961–2015 were collected at 15 hydrological and 60 meteorological stations that were widely distributed in the basin. Changing trends, periodicity, and abrupt changes of hydro‐climatic variables were detected using the non‐parametric Mann–Kendall test, the empirical mode decomposition method, and Pettitt's test. Results showed that annual sediment load presented significantly decreasing trends at 12 hydrological stations. Annual rainfall erosivity showed a mixed tendency, with the changing trends varying among different regions. A 3‐year periodicity was identified in the annual sediment load at three main stream gauging stations. Abrupt changing points in sediment load primarily occurred in the 1990s and early 2000s at all of the 15 hydrological stations, which were largely attributed to human activities. The increase in vegetation cover was responsible for approximately 40.6%, 37.4%, and 54.7% of the sediment load reduction in the main stream of the Weihe River, the Jinghe River, and the Beiluohe River, respectively. Meanwhile, terrace construction accounted for 19.7%, 43.8%, and 9.9% of the sediment variation, respectively. Conversely, precipitation change accounted for 5.7%, 12.4%, and 8.3% of sediment load reduction, respectively. Overall, vegetation restoration and terrace construction were found to be the two dominating factors for sediment load reduction in the study area. [ABSTRACT FROM AUTHOR]

River runoff and suspended sediment play a critical role in the chemical, physical, biological processes of Earth's ecosystems. We assessed the temporal changes in runoff and sediment load at both the annual and event scales in the Gushanchuan watershed in the middle reaches of the Yellow River. A total of 330 events, from 1955 to 2018, were selected to evaluate the relationships between rainfall, runoff, and suspended sediment load at the Gaoshiya gauging station. Significant reductions were examined in the maximum runoff peaks, suspended sediment concentration, total runoff, suspended sediment yield, and ratio of event runoff to annual total, whereas the ratio of event sediment yield to annual total remained relatively stable. Hysteresis analysis suggested that the complex loops, anti‐clockwise, and figure‐eight loops accounted for 93.7% of the total events in the watershed. High positive correlations were observed between the flood‐event sediment yield, runoff volume, maximum runoff peaks, and total rainfall amount. The flow‐sediment relationship can be well fitted by the proportional model, and was weaker in 1997–2018 than those in the periods of 1955–1979 and 1980–1996. Runoff during the rising limb of the event significantly contributed to the total runoff and sediment yield. Land use changes and various soil conservation practices were responsible for the decrease in the flood frequency and magnitude. The results of this study provide useful insights into the relationships between rainfall, runoff, and suspended sediment dynamics, and their responses to soil conservation practices. [ABSTRACT FROM AUTHOR]

Investigating the changes in streamflow regimes in response to various influencing factors contributes to our understanding of the mechanisms of hydrological processes in different watersheds and to water resource management strategies. This study examined streamflow regime changes by applying the indicators of hydrologic alteration method and eco‐flow metrics to daily runoff data (1965–2016) from the Sandu, Hulu and Dali Rivers on the Chinese Loess Plateau, and then determined their responses to terracing, afforestation and damming. The Budyko water balance equation and the double mass curve method were used to separate the impacts of climate change and human activities on the mean discharge changes. The results showed that the terraced and dammed watersheds exhibited significant decreases in annual runoff. All hydrologic metrics indicated that the highest degree of hydrologic alteration was in the Sandu River watershed (terraced), where the monthly and extreme flows reduced significantly. In contrast, the annual eco‐deficit increased significantly, indicating the highest reduction in streamflow among the three watersheds. The regulation of dams and reservoirs in the Dali River watershed has altered the flow regime, and obvious decreases in the maximum flow and slight increases in the minimum flow and baseflow indices were observed. In the Hulu River watershed (afforested), the monthly flow and extreme flows decreased slightly and were categorized as low‐degree alteration, indicating that the long‐term delayed effects of afforestation on hydrological processes. The magnitude of the eco‐flow metrics varied with the alteration of annual precipitation. Climate change contributed 67.47% to the runoff reduction in the Hulu River watershed, while human activities played predominant roles in reducing runoff in the Sandu and Dali River watersheds. The findings revealed distinct patterns and causes of streamflow regime alteration due to different conservation measures, emphasizing the need to optimize the spatial allocation of measures to control soil erosion and utilize water resources on the Loess Plateau. [ABSTRACT FROM AUTHOR]

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]

Aims: Since the 1970s, extensive croplands were converted to forest and pasture lands to control severe soil erosion on the Loess Plateau of China. We quantify the direct and indirect effects of vegetation restoration on runoff and sediment yield on hillslopes in the field to improve environmental governance. Methods: An artificial rainfall experiment at a rainfall intensity of 120 mm h−1 and a slope gradient of 22° were used to distinguish the effects of vegetation restoration on runoff and sediment yield. Results: Compared to the farmland slopes, vegetation restoration directly prolonged the time-to-runoff by 140%, reduced the runoff rate by 20%, and increased the soil infiltration capacity by 15%. Vegetation restoration indirectly delayed the time-to-runoff by 120%, reduced the runoff rate and sediment yield rate by 50% and 94%, respectively, and increased the soil infiltration capacity by 58% on the hillslopes with vegetation restoration. Conclusions: The direct effects of vegetation restoration on runoff and sediment yield were lower than its indirect impacts. Vegetation cover, decreases in soil bulk density, and increases in belowground root biomasses and > 0.25 mm aggregate stability were the primary causes of runoff and sediment yield reduction on the slopes with vegetation restoration. [ABSTRACT FROM AUTHOR]

Terrace identification is the basis for understanding quantity, quality, and land covers of terraces and their effects on agriculture production and various surface processes, for example, hydrological and ecological processes. However, there are some drawbacks and limitations in the automatic extraction of terraces, such as difficulty of outlining the overall boundary for individual terrace and the limitation of applying methods and parameters. In this study, we used machine learning methods on the basis of Geographic Object‐Based Image Analysis using K‐nearest neighbours and spectral angle mapper algorithms to extract terraces in the hilly and gully regions on the Loess Plateau, China. This study relied on medium‐resolution image Landsat‐8 combined with Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model to extract the overall boundary of terraces and relies on high‐resolution images GaoFen‐1 to extract the terraced edges of terraces. It used the methods of principal component analysis and Laplacian convolution filter to enhance and extract terraced edges inside of the boundary of terraces. Our estimates are with overall accuracy of 62.2% in K‐nearest neighbours and 74.8% in spectral angle mapper methods, indicating the advantages of the proposed method despite the use of much lower resolution data than previous studies that used both high‐resolution terrain and remote sensing imageries data. This study highlights the importance of using appropriate methods plus reasonable spatial resolution of remote sensing data for outlining the overall boundary of terraces in the hilly and gully regions. [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]

• Sharp decline in agricultural land area, water yield and sediment load were observed from 2000 to 2015. • We optimized land use based on the trade-off between ecosystem services on the hydrological response unit (HRU) scale. • Conservation scenario achieved higher soil conservation at cost of less water yield and agriculture. • The spatial configurations of the GfG measures need a detailed adjustment. Since the implementation of the Grain for Green (GfG) project in 1999, the environment of China's Loess Plateau has been largely restored, and soil erosion has been controlled in places. However, new problems associated with food and river water resource security have arisen. Thus, to achieve sustainable development, it is critical to integrate agriculture and resource conservation with soil conservation. In this study, the Soil and Water Assessment Tool (SWAT) model was used to investigate the relationship between sediment load and water yield in the Yanhe watershed in the Loess Plateau. The results were as follows: (1) Sharp declines in agricultural land area (43.78%), water yield (38.48%) and sediment load (38.71%) have occurred since the implementation of the GfG project. (2) Based on the spatial heterogeneity of hydrological response units (HRUs), we proposed a simple method for land use planning that considers river water resources, agriculture and sediment loading and then established a balanced conservation scenario. Compared with the scenario in 2030 (planning scenario), the conservation scenario reduced the sediment yield by 6.4%, increased the water yield by 4.5%, and increased agricultural land by 80.1%. Our results can be used to support spatially targeted land use planning, which is beneficial for the sustainable development of the GfG project. [ABSTRACT FROM AUTHOR]

Northwest China is characterized by a high water deficit and regular water resource shortages. These issues have become limiting factors for agricultural and socioeconomic development. Based on a trend-preserving method of bias correction, we calibrated the maximum temperature and minimum temperature in four CMIP5 GCMs (CNRM, IPSL, BCC, and CMCC). Then, we investigated variations in the regional crop water requirement (CWR) in the total growth stages for five main crops (cotton, spring corn, summer corn, spring wheat, and winter wheat) in the past (1961–2005) and future (2006–2100). The results suggest that the MK test yielded insignificant decreasing CWR trends in the total growth stages of cotton (0.10 mm/year), spring corn (0.13 mm/year), and spring wheat (0.05 mm/year) and insignificant increasing trends for summer corn (0.02 mm/year) and winter wheat (0.32 mm/year) historically. In the future period, for the same type of crops (cotton), the CWRs in all scenarios (RCP 2.6, 4.5, and 8.5 scenarios) for all GCMs exhibited significant positive trends; for the same GCM (BCC), the CWRs projected for five major crops in the RCP 4.5 and 8.5 scenarios all exhibited extremely significant MK trends (99%); in addition, the CWRs' rate increases of the five crops projected in RCP8.5 scenario by BCC exhibited the following order: winter wheat (1.25 mm/year), summer corn (1.15 mm/year), spring corn (1.02 mm/year), cotton (0.97 mm/year), and spring wheat (0.87 mm/year). The maximum CWRs of winter wheat were mainly observed in southeastern Northwest China, while those of the other four crops occurred in southern Xinjiang. [ABSTRACT FROM AUTHOR]

Soil and water conservation measures including terracing, afforestation, construction of sediment-trapping dams, and the 'Grain for Green Program' have been extensively implemented in the Yanhe River watershed, of the Loess Plateau, China, over the last six decades, and have resulted in large-scale land use and land cover changes. This study examined the trends and shifts in streamflow regime over the period of 1953-2010 and relates them to changes in land use and soil and water conservation and to the climatic factors of precipitation and air temperature. The non-parametric Mann-Kendall test and the Pettitt test were used to identify trends and shifts in streamflow and base flow. A method based on precipitation and potential evaporation was used to evaluate the impacts of climate variability and changes in non-climate factors changes on annual streamflow. A significant decrease ( p = 0.01) in annual streamflow was observed related to a significant change point in 1996, mostly because of significant decreases in streamflow ( p = 0.01) in the July to September periods in subsequent years. The annual base flow showed no significant trend from 1953 to 2010 and no change point year, mostly because there were no significant seasonal trends, except for significant decreases ( p = 0.05) in the July to September periods. There was no significant trend for precipitation over the studied time period, and no change point was detected. The air temperature showed a significant increasing trend ( p < 0.01), and 1986 ( p < 0.01) was the change point year. The climate variability, as measured by precipitation and temperature, and non-climate factors including land use changes and soil and water conservation were estimated to have contributed almost equally to the reduction in annual streamflow. Soil and water conservation practices, including biological measures (e.g. revegetation, planting trees and grass) and engineering measures (such as fish-scale pits, horizontal trenches, and sediment-trapping dams) play an important role in reduction of the conversion of rainfall to run-off. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Water conservation capacity showed an insignificant increasing trend. • Landscape patterns tend to be fragmented and diversified. • Increased landscape fragmentation and diversity was conducive to the improvement of water conservation. • Vegetation coverage played an important promoting effect on water conservation. With the accelerating changes of land use/cover caused by natural and human factors, landscape pattern has undergone significant changes. Given the scarcity of water resources and the degradation of ecological functions in arid and semi-arid regions of China, it is necessary to analyze the impact of landscape pattern changes on water conservation. Taking the Wei River Basin (WRB) as the research area, based on water balance equations, FRAGSTATS 4.2 software, and correlation analysis method, this study explored the spatiotemporal distribution characteristics of water conservation and landscape pattern in the WRB from 1990 to 2020, as well as the correlations between the two. The results showed that from 1990 to 2020: (1) the water conservation capacity (WCC) showed no insignificant change trend (P > 0.05) in sub water basins as well as the entire WRB, and it presented a spatial distribution pattern of more in the south and west, and less in the north and east; (2) the landscape diversity and fragmentation of the WRB have increased, and the patch shapes tended to be complex, while connectivity and agglomeration between patches decreased; (3) The WCC had significant negative correlations with the Contagion Index (CONTAG), connectivity index (COHESION), and largest patch index (LPI), while had significant positive correlations with landscape shape index (LSI), Shannon diversity index (SHDI), and separation index (SPLIT), indicating that the increase of landscape fragmentation and diversity was conducive to the improvement of WCC. In the process of ecological landscape planning and optimization, the fragmentation degree of landscape can be appropriately increased. (4) Vegetated grassland, forestland, and farmland were the main sources of WCC, with average WCC values of 81.90, 68.04, and 8.72 mm, respectively. NDVI of the watershed increased significantly (P < 0.01) during the research period and showed a significant positive correlation with WCC, indicating the promoting effect of increasing vegetation coverage on WCC. Relevant results may provide referential information for ecological restoration and optimization of landscape pattern in arid/semiarid regions. [ABSTRACT FROM AUTHOR]

Global climate change has contributed to frequent occurrence of extreme precipitation events, resulting in more severe natural disasters and restricting regional development. The Qinling-Daba mountains region (Qinba) is a transitional zone in central China with high ecological vulnerability and sensitivity. It is therefore essential to investigate the dynamics of precipitation extremes in the region. In this study, spatiotemporal variations of extreme precipitation events were analyzed at the monthly, seasonal and annual timescales based on long-term daily precipitation dataset at 30 meteorological stations over the Qinba during 1961–2017. The results indicated all of the selected ten extreme precipitation indices exhibited non-significant trends at the annual scales. Seasonally, most of extreme precipitation indices decreased in spring, autumn and winter, and increased in summer, whereas consecutive dry days (CDD) increased in all seasons. At the monthly scales, wet precipitation extremes mostly occurred in July, and upward trends of extreme precipitation events dominated in February, June, July and August except for CDD. Spatially, regionwide increases in extreme precipitation events mainly distributed in the eastern and southern Qinba, whereas the north and west were dominated by decreasing trends. Most of atmospheric circulation indices, especially Arctic Oscillation (AO), Southern Oscillation Index (SOI) and Western Pacific Index (WP) were associated with extreme precipitation events at monthly and annual scales. East Asian Summer Monsoon Index (EASMI) and South China Sea Summer Monsoon Index (SCSSMI) strongly influenced extreme precipitation events in summer over the Qinba. Our results are conducive to understanding the variations of extreme precipitation events at the monthly, seasonal and annual scales, and these will be valuable for formulating the corresponding countermeasures at different timescales over the Qinba. [ABSTRACT FROM AUTHOR]

Abstract Investigating the suspended sediment dynamic is useful for gaining a more comprehensive understanding of runoff and sediment yield process. The study analyzes the sediment flow behavior in relation to the flood patterns in the Xichuan River catchment on the Loess Plateau. Based on 23-year hydrological data collected from Zaoyuan hydrological station and K-medoids clustering method, one hundred and twelve flood events data were classified into four flood patterns. The hydrologic features of different flood patterns exhibit significant differences. The values of the mean runoff depth, the mean flood duration, and the mean flood peak discharge decreased as the following order: Pattern A > Pattern C > Pattern D > Pattern B. Each flood pattern results in differing levels of the event sediment yield (SY), the SY of Pattern A (10,275.33 t·km−2) and Pattern C (1196.39 t·km−2) were larger than those from Pattern B (218.84 t·km−2) and Pattern D (693.84 t·km−2). These results indicated that greater attention should be paid to Pattern A and Pattern C because of the largest sediment delivery effect. Multiple stepwise regressions analysis suggested that the contribution of main runoff-related factors to event sediment yield varied with different flood patterns. In addition, hysteretic analysis between suspended sediment concentration and runoff suggested that counter-clockwise and figure-eight loops were the dominant loops. The results provided a useful information to flood pattern classifications and suspended sediment dynamics research, and enriched the sediment control theory at the watershed scale. Highlights • Screen the key/dominant hydrological variables that have a major influence on sediment yield and delivery • Explore sediment flow behavior under different flood regimes • Identify the sediment sources based on different SSC-Q hysteresis loops [ABSTRACT FROM AUTHOR]

[Display omitted] • Sediment load decreased significantly due to trapping effects of cascade reservoirs. • The change points corresponded to the timing of gigantic reservoirs construction. • Cascade reservoirs contributed 88% and 90% to streamflow and sediment load reduction. • Reservoirs greatly altered seasonal distribution of flow and flood peaks processes. Large reservoirs are widely built along rivers for flood control, hydropower generation, water supply for industry and agricultural production, and recreation. Many large reservoirs/dams built to provide multiple functions for local people are strongly influenced by the downstream flow and sediment discharge in the upstream of the Yellow River, China. In this study, we assessed the changes in the river flow and sediment discharge in responses to the construction of cascade reservoirs/dams by using continuously hydrological time series observed at six stations during 1956–2018. The temporal change in the streamflow was insignificant, but the sediment load decreased dramatically due to the trapping effects of the cascade reservoirs. The change points were detected in 1969 and 1986, which were consistent with the timing of the construction of gigantic reservoirs. We then applied the abrupt changing points to divide the whole time series into a reference period (1956–1968) and two changing periods (1969–1986 and 1987–2018). The linear regression and three machine learning models were employed to reconstruct the natural streamflow and sediment load at the downstream station, before quantifying their responses to cascade reservoirs. The annual mean streamflow and sediment load decreased by 21% and 84%, respectively, after constructing the Longyangxia and Liujiaxia reservoirs. Cascade reservoirs contributed 85.39% and 94.91% to the decreases in the streamflow and sediment discharge, respectively. Hydrological regimes have been greatly altered by the 13 cascade reservoirs, with seasonal redistribution of the streamflow and flood peak reduction because their high trapping efficiencies exceed 95%. These findings indicate that large and medium sized reservoirs have drastically altered the streamflow and sediment load, thereby intensely influencing the fluvial processes in the upstream of the Yellow River. [ABSTRACT FROM AUTHOR]

• Conservativeness and consistency for individual tracer were evaluated. • The optimal tracers set varied in different flood process. • Bare land was the predominant source to the total sediment load within flood events. • The weathered sandstone area is the critical region for soil loss control. Identifying critical soil erosion areas and sediment sources are essential for sediment control and water resources management in the watershed, especially in the severely eroded northern Loess Plateau, China. In this study, we collected suspended sediment samples at the hydrological stations to identify the sediment source dynamics during flood events in a highly erodible basin, the Huangfu River basin in the Northern Loess Plateau. A total of 6 flood events were sampled during 2016 and 2018 for investigation, the flow discharge was featured by a rapid rising limb and a slow falling limb. Compared with the sediment sources, the silt fraction in the suspended sediments was enriched and the sand fraction in the suspended sediment was depleted. The dominant particle grain size of suspended sediments was coarse sand (56.89%), higher than silt (41.81%) and clay (1.3%). The sediment sources were estimated using the FingerPro unmixing model based on the conservativeness index (CI) and consensus ranking (CR) methods. The results of the unmixing model reveal that the bare land was the predominant source of suspended sediments, ranging from 40% to 57%, which was much higher than farmland (27 ∼ 31%) and grassland (16 ∼ 25%). Our findings imply that the bare land (weathered sandstone area) is the critical region for soil loss control in the Huangfu River basin. A combination of vegetation restoration measures and engineering measures are proposed to improve the sustainable development of ecological environment in the basin. [ABSTRACT FROM AUTHOR]

An improved understanding of the temporal variations in soil erosion rates and sediment sources is necessary to identify the main areas prone to soil erosion and to effectively implement soil and water conservation measures. In this study, we selected two dam-controlled watersheds (Xiaoshilata and Yangjiagou) on the northern Loess Plateau, China, and determined the temporal variations in the sediment yield. The sedimentation upstream of the dams showed that there were 31 and 9 flood couplets in the Xiaoshilata (1958–1972) and Yangjiagou watersheds (2007–2011), respectively, which have trapped 16.5 × 10 4 t and 3.38 × 10 4 t of sediment, respectively. The estimated specific sediment yield was approximately 173.6 t/ha/a and 106.1 t/ha/a in the Xiaoshilata and Yangjiagou watersheds, respectively. A multivariate mixed model was applied to identify the different sediment sources. The results indicated that weathered sandstone contributed approximately 61.52% of the total sediment, and the remaining sediment loss was from bare loess soil (32.54%) and grassland (5.94%) in the Xiaoshilata watershed. In the Yangjiagou watershed, approximately 66.8% of the sediment originated from weathered sandstone, whereas bare loess and grassland accounted for 17.5% and 15.7% of the sediment yield, respectively. Based on these findings, we recommend that comprehensive soil conservation measures are needed to soil erosion control for the permanent steep gullies due to high sediment contribution. The sedimentation behind the check dams provides an indirect method for estimating the sediment yield in ungauged basins. [ABSTRACT FROM AUTHOR]

Large-scale sediment control efforts on the Loess Plateau of China and resulting reductions in sediment yield have been documented. However, it remains unclear how these control works affect the soil erosion rates and sediment loads at the catchment scale. A combination of field work and modeling exercises was used to examine the effects of land use changes and check dams on the variation of sediment yield at the catchment scale. The Huangfuchuan catchment was selected as a case study. The sediment distributed delivery (SEDD) model was calibrated using both observed sediment load data and sedimentation rates derived from check dams. The study catchment suffered important land use changes with increasing grassland and decreasing bare land, sandy area and arable land from 1990 to 2006. By 2009, 502 check dams with a total storage capacity of 571 Mm 3 had been built in the study area. Relatively good agreement can be seen between observations and model simulation results. Model applications showed that in a scenario without check dams, the land use changes between 1990 and 2006 caused a remarkable reduction of 31.4% in sediment yield. The check dams without land use changes with respect to the 1990 scenario reduced 51.9% of the sediment yield in the study area. The combination of land uses and check dam construction in 2006 reduced the sediment yield by approximately 80%. Our results indicate that check dams are efficient sediment control measures; however, the accumulation of sediment in check dams may create costly problems in the operation of dams and failures because of their short lives. Therefore, sustainable solutions are needed for sediment management in the check dams, such as sediment pass-through, flushing, or mechanical removal, and a reasonable construction plan is also needed for flood control. [ABSTRACT FROM AUTHOR]

• Annual sediment load decreased in 77% river basins, but increased insignificant in western China. • Large reservoirs led to abrupt changes in mainstem stations, and large-scale conservation measures were responsible for shifts in tributaries. • Dominant climate variables affecting sediment load were P wet , R12 and FSPTOT. • Sediment load changes were related to extreme rainfall in most rivers, and sensitive to temperature in the Northwest River Basin. Global warming has led to increase in climate extremes, which altered both hydrological cycles and soil erosion processes. However, the responses of river sediment load to climate change, especially climate extremes have not been well understood due to a lack of comprehensive assessment. This study investigated the temporal trends and spatial patterns of sediment load at 70 hydrological stations during the period of 1956–2019 in ten major river basins in China. Both the partial linear square regression model and the double mass curve method were used to quantify the contribution of key climatic indices and anthropogenic driving forces. Overall, the annual total sediment load exhibited a significant negative trend (P < 0.01), decreasing from 1842.18 Mt/yr in 1960 s to 322.72 Mt/yr in 2010 s (82.48 %). The significant decline of sediment load was particularly obvious in the Yangtze River basin and the Yellow River basin. The abrupt changes of sediment load mostly occurred in 1985–2000. Human activities were primarily response for sediment load changes in most basins. The sediment load in mainstream was mainly regulated by reservoirs, while the tributaries were largely affected by soil and water conservation measures. Intensive human activities have led to substantial changes in land surface and resulted in weakened correlation between sediment load and climate extremes. Generally, precipitation, erosive rainfall and precipitation amount in flood period were closely related to sediment load. In the Southwest River basin and Northwest River basin, the sediment load had a relatively good relationship with extreme temperature, which was related to alpine snowmelt and permafrost degradation due to climate warming. This study provides good insights for a better understanding of the interaction between river sediment load and climate extremes variables, which will be valuable for decision-making in river basin management. [ABSTRACT FROM AUTHOR]

• A connectivity index was coupled with a soil erosion model to estimate sediment yield. • Afforestation led to evident decreases in both the connectivity and the sediment delivery ratio. • The modeled sediment yield showed a 60.7% reduction due to changes in land use and check dams. The hydrological connectivity on the Loess Plateau has been greatly altered by soil and water conservation measures in the past six decades, leading to significant reduction in sediment load. Nevertheless, how these measures affect sediment transport at the catchment scale remains unclear. This study coupled an index of connectivity (IC) with the Revised Universal Soil Loss Equation (RUSLE) model to estimate the sediment yield in the Yanhe catchment (7,725 km2). The model was used to assess the impacts of land use changes and check dam construction on sediment delivery. The land use maps showed increasing grassland (10.3%) and decreasing arable land (12.3%) from 1990 to 2010. The ranges of IC between the two land use scenarios showed significant changes with an average of 0.3 in 1990 and −0.5 in 2010. Land use changes resulted in average sediment delivery ratio decreasing from 0.39 in 1990 to 0.30 in 2010. The model was calibrated by annual sediment load at a gauging station, covering 5,852 km2 of the catchment and by sedimentation rates behind check dams in a representative sub-catchment. Measured and simulated sediment load showed consistent agreement, suggesting acceptable model performance. An approximately 60.7% reduction in sediment yield was attributed to land use changes and increasing check dams′ construction from 1990 to 2010. This study provided a good example of combining the IC with a soil erosion model to identify spatial patterns and temporal variations in sediment yield due to soil conservation measures. [ABSTRACT FROM AUTHOR]

The sediment load on the Chinese Loess Plateau has sharply decreased in recent years. However, the contribution of terrace construction and vegetation restoration projects to sediment discharge reduction remains uncertain. In this paper, eight catchments located in the Loess Plateau were chosen to explore the effects of different driving factors on sediment discharge changes during the period from the 1960s to 2012. Attribution approaches were applied to evaluate the effects of climate, terrace, and vegetation coverage changes on sediment discharge. The results showed that the annual sediment discharge decreased significantly in all catchments ranging from -0.007 to -0.039 Gt·yr -1 . Sediment discharge in most tributaries has shown abrupt changes since 1996, and the total sediment discharge was reduced by 60.1% during 1997-2012. We determined that increasing vegetation coverage was the primary factor driving the reductions in sediment loads since 1996 and accounted for 47.7% of the total reduction. Climate variability and terrace construction accounted for 9.1% and 18.6% of sediment discharge reductions, respectively., (Copyright © 2018. Published by Elsevier B.V.)

Grasslands are an important component of terrestrial ecosystems that play a crucial role in the carbon cycle and climate change. In this study, we collected aboveground biomass (AGB) data from 223 grassland quadrats distributed across the Loess Plateau from 2011 to 2013 and predicted the spatial distribution of the grassland AGB at a 100-m resolution from both meteorological station and remote sensing data (TM and MODIS) using a Random Forest (RF) algorithm. The results showed that the predicted grassland AGB on the Loess Plateau decreased from east to west. Vegetation indexes were positively correlated with grassland AGB, and the normalized difference vegetation index (NDVI) acquired from TM data was the most important predictive factor. Tussock and shrub tussock had the highest AGB, and desert steppe had the lowest. Rainfall higher than 400 m might have benefitted the grassland AGB. Compared with those obtained for the bagging, mboost and the support vector machine (SVM) models, higher values for the mean Pearson coefficient (R) and the symmetric index of agreement (λ) were obtained for the RF model, indicating that this RF model could reasonably estimate the grassland AGB (65.01%) on the Loess Plateau.