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Abstract: The YinNan Irrigation District (YNID) is located in the upper reaches of the Yellow River in NingXia, China. Its drainage system was constructed between the 1950s and 1970s to maintain salt and water balances in the district. The system, however, has been reported draining the agricultural lands excessively, resulting in frequent irrigations and large amount of drainage discharge into the Yellow River each year. This paper presents a comprehensive analysis of current drainage practices in the YNID and discusses the feasibility of controlled drainage in order to mitigate the negative impact of agricultural drainage. Based on historical records and available information, drainage discharge has been estimated for different crop fields and ditches. The results show that for the major water use crop, rice, controlled drainage may reduce subsurface discharge through field ditches up to 94%. For wheat and corn, the benefit of controlled drainage is not significant because the major drainage discharge is directly through the main ditch system and the Yellow River channel. The rotational cropping nature and local water management tradition, however, make controlled drainage a very attractive option for water savings and reducing water pollution to the Yellow River. [Copyright &y& Elsevier]

Water scarcity in the Bojili irrigation District, which is located in the Shandong province in China, affects the management of the irrigation system and has led to the development of water storage functions inside the system. In particular, the irrigation and drainage scheme is used for short-term water storage whereas groundwater is used for long-term storage which is replenished during the monsoon season and drawn from when crop water requirements are not satisfied by surface irrigation. In this paper the storage functions are quantified. The role of groundwater, in relation to rainfall and irrigation depths, is analysed in detail. This analysis, which was carried out at the district and at sub-system scales, is based on data collected from fifty five observation wells between 1991 and 1996 at a 10-day time intervals. The sub-systems, called “divisions”, represent the areas for which irrigation-related information is available. Rainfall, groundwater levels and irrigation data are consistent. They demonstrate the inequity of water allocation between upstream and downstream water users. Accordingly strategies for water management differ between these users. These strategies only partially compensate the effects of scarcity demonstrated by decreasing cropping intensities from upstream to downstream parts of the District. [ABSTRACT FROM AUTHOR]

This paper illustrates the importance of river ice accumulations in changing river channel geometry based on field investigations carried out at the Hequ gauging station on the Yellow River in China. A relationship is established between riverbed deformation and ice accumulation. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation management is of critical importance for the sustainable development of surface water resources. Sanmenxia Dam, located on the middle reach of the Yellow River, in China, is notorious for its severe sedimentation problems. Because of the alarming rate of loss of reservoir storage capacity and the unacceptable negative impact induced by the rapid upstream extension of sediment deposited in the river's backwater region, the dam has been reconstructed to provide high sediment releasing capacity, and the dam operation has been changed in order to achieve a balance between sediment inflow and outflow. As a result, the dam is still providing the basin with flood control, irrigation, and hydropower generation, even though some benefits are lower than the original design. Complex sedimentation processes in response to the dam reconstruction and changes of dam operation are discussed in this paper. The engineering experiences and management practices of Sanmenxia Dam are valuable assets to the sustainable use of reservoirs built on sediment-laden rivers. [ABSTRACT FROM AUTHOR]

Desiccation of the Yellow River, the cradle of the Chinese civilization and the second longest river in China since the 1970s, has created serious socioeconomic, environmental and ecological problems. This paper analyzes the water shortage problem in the Yellow River and evaluates the effects of demand management and the interbasin transfer -South Water Northward Transfer Project - in alleviating the problem. Although China has initiated a series of demand management and pollution control initiatives, these programs alone cannot solve the chronic water shortage problem in the Yellow River Basin. While facing multiple challenges and controversies, implementation of the South Water Northward Transfer Project is necessary to mitigate the water shortage crisis in the Basin. However, the implementation of the Transfer Project is only a partial solution to the Yellow River chronic water shortage problem. China should actively implement and enforce its demand management programs and pollution control policies to make sustainable use of its limited fresh water resources. [ABSTRACT FROM AUTHOR]

This paper presents the impacts of frazil ice jams on the variation in water level at the Hequ Reach of the Yellow River in China. Based on both field observations and experimental studies, it is found that both the evolution of frazil ice jams and the associated variation in water level depend upon an interesting interaction between hydraulic variables during the ice-jammed period. In particular, the critical Froude number governing the formation of river ice jams and their upstream propagation is about 0.09. The water level during ice-jammed periods depends not only on the slope of the water surface and the water level under open-water conditions with the same discharge, but also on the length of the ice jam and the ice concentration in the water. Moreover, the field investigations show that the thickness of river ice strongly influences the variation in water level during ice-jammed periods. Empirical relationships are derived to quantify the relationship between the highest water level during ice periods and related physical parameters. To confirm the field results, and to explore the influence of ice discharge on the variation in water level, experimental studies were also conducted. These results confirm that the ice concentration plays a key role in the variation in water level and the jam thickness. Given the complexity of the jamming processes, surprisingly good agreement is observed between field and experimental investigations. [ABSTRACT FROM AUTHOR]

This paper presents the impacts of frazil ice jams on the variation in water level at the Hequ Reach of the Yellow River in China. Based on both field observations and experimental studies, it is found that both the evolution of frazil ice jams and the associated variation in water level depend upon an interesting interaction between hydraulic variables during the ice-jammed period. In particular, the critical Froude number governing the formation of river ice jams and their upstream propagation is about 0.09. The water level during ice-jammed periods depends not only on the slope of the water surface and the water level under open-water conditions with the same discharge, but also on the length of the ice jam and the ice concentration in the water. Moreover, the field investigations show that the thickness of river ice strongly influences the variation in water level during ice- jammed periods. Empirical relationships are derived to quantify the relationship between the highest water level during ice periods and related physical parameters. To confirm the field results, and to explore the influence of ice discharge on the variation in water level, experimental studies were also conducted. These results confirm that the ice concentration plays a key role in the variation in water level and the jam thickness. Given the complexity of the jamming processes, surprisingly good agreement is observed between field and experimental investigations. [ABSTRACT FROM AUTHOR]

Using the measured data on no-flow events in the Lower Yellow River since 1972, this paper presents an approach to describe the no-flow status in terms of a comprehensive indicator. The severity levels of no-flow events are identified by cluster analysis. Furthermore, the relation between severity levels and incoming water from upstream and its variance is well established with a BP-typed Artificial Neural Network (ANN), which is helpful to identify the complex response of the severity level to flow characteristics. The availability of the approach for quantitative description and prediction of no-flow events is discussed through comparisons between predicted and measured results in the Lower Yellow River. [ABSTRACT FROM AUTHOR]

Transjurisdictional water pollution problems are increasing in number and are becoming a significant governance problem in China. A large number of transjurisdictional water pollution disputes that have far-reaching social effects are occurring between provinces and are also frequent between municipalities, counties, towns, and villages. In this paper, several transjurisdictional water pollution cases in China, particularly in the Yellow River Basin, are discussed. The problems and causes for transjurisdictional water pollution are addressed. There are many causes for transjurisdictional water pollution problems although the key reasons are the rapid economic development, the failure of local authorities to enforce the existing laws and to implement administrative decisions, as well as inadequacies in the legal framework. Other factors include poor technology, shortage of funds, the institutional division of jurisdiction and management over water quantity and quality both administratively and legally, the lack of transparency in the decision-making process, insufficient public participation and information disclosure, poor communication, and lack of involvement of stakeholders in basin or sub-basin organizations. [ABSTRACT FROM AUTHOR]

The Yellow River has been intensively affected by human activities, particularly in the past 50 years, including soil–water conservation in the upper and middle drainage basin, flood protection in the lower reaches, and flow regulation and water diversion in the whole drainage basin. All these changes may impact sedimentation process of the lower Yellow River in different ways. Assessing these impacts comprehensively is important for more effective environmental management of the drainage basin. Based on the data of annual river flow, sediment load, and channel sedimentation in the lower Yellow River between 1950 and 1997, the purpose of this paper is to analyze the overall trend of channel sedimentation rate at a time scale of 50 years, and its formative cause. It was found in this study that erosion control measures and water diversion have counteractive impacts on sedimentation rate in the lower Yellow River. Although both annual river flow and sediment decreased, there was no change in channel sedimentation rate. A regression analysis indicated that the sedimentation in the lower Yellow River decreased with the sediment input to the lower Yellow River but increased with the river flow input. In the past 30–40 years, the basin-wide practice of erosion and sediment control measures resulted in a decline in sediment supply to the Yellow River; at the same time, the human development of water resources that required river flow regulation and water diversion caused great reduction in river flow. The former may reduce the sedimentation in the lower Yellow River, but the reduction of river flow increased the sedimentation. When their effects counterbalanced each other, the overall trend of channel sedimentation in the lower Yellow River remained unchanged. This fact may help us to better understand the positive and negative effects of human activities in the Yellow River basin and to pay more attention to the negative effect of the development of water resources. The results of this study demonstrate that, if the overuse of river water cannot be controlled, the reduction of channel sedimentation in the lower Yellow River cannot be realized through the practice of erosion and sediment control measures. [ABSTRACT FROM AUTHOR]

The Loess Mesa Ravine Region and the Loess Hill Ravine Region, cover 200,000 km2 of the Loess Plateau in China and have serious problems of soil and water erosion. Two primary ways to control the sediment pouring into the Yellow River from this area are planting and engineering measures. The former is not suitable for the Loess Plateau due to the arid climate and the barren soil, while some of the latter means, such as terrace farmlands, are vulnerable to floods. As a widespread engineering measure, the check-dam system in gullies is one of the most effective ways to conserve soil and water in the Loess Plateau. At present, the amount of sediment retained by check-dam systems is the largest of all methods and the potential is promising. The dam farmlands so created have become important high-yield croplands or orchards with enriched fertile soil and ample water. This paper reviews the history and principles of check-dams and discusses future theoretical and experimental studies which are needed for the further implementation of this system. [Copyright &y& Elsevier]

According to the principle of procedure control and the characteristic of stochastic of inflow and water demands, this paper deals with the application of adaptive control to a water resources regulation system. The main control objective is to approach the vested target of water resources allocation by controlling the reservoir discharge and water demand. The adaptive control implemented is based on the linear quadratic control approach. Models of water balance, reservoir adjusted model and allocation model are used for the control purposes. The results show the performance of this adaptive scheme and its ability to control the water resources allocation process. [ABSTRACT FROM AUTHOR]

Soil loss, water shortage, flooding, sedimentation and water pollution are the major problems affecting the sustainable development of the Yellow River basin. Their impacts and management strategies are briefly discussed in this paper. The integrated management strategy, which includes one ultimate goal, four standards, nine countermeasures, and the concept of “three Yellow Rivers,” is a contemporary management strategy and represents the vision of the Chinese government and engineers for the sustainable development of the Yellow River basin. [ABSTRACT FROM AUTHOR]

The streamflow over the Yellow River basin is simulated by using the high-resolution Regional Integrated Environmental Model System (RIEMS), and an off-line Large-scale Routing Model (LRM). The RIEMS was designed and has been developed by the Global Change System for Analysis, Research and Training Regional Center for Temperate East Asia (START/TEA) since 1991 and has a good capability to simulate the regional climate of East Asia. The LRM is based on the assumption of linearity and time invariance and can calculate the horizontal travel of water. The RIEMS-LRM allows the direct comparison of predicted and observed streamflow data for large-scale rivers. The application of the RIEMS-LRM to the upper reaches of the Yellow River verifies that the coupled model system has the capability to simulate the streamflow over a large-scale river. Furthermore, the paper discusses the reasons leading to simulation errors. [ABSTRACT FROM AUTHOR]

Although dike-break and dam-break processes have similar unsteady and discontinuous hydrodynamic characteristics, there are significant differences. In general, dam-break simulations focus on the flood discharge, whereas dike-break simulations are required to provide detailed information on the hydraulic and breach evolution processes, such as pit-scour and breach-expansion. In order to overcome the difficulties inherent in applying existing dam-break models to dike-breaks, this paper presents an integrated model that combines the shallow water, sediment transport, riverbed deformation and breach-expansion equations. A Godunov-type finite volume method is used for the flow simulation, based on a fixed quadtree grid system. The hydrodynamic aspects of the model are validated for an idealized rectangular dam break. A representative reach in the Yellow River is selected at a location where there is a significant risk of a dike-break, and full-scale topographic and hydrologic data are available. Typical dike-break processes are successfully simulated, with predicted hydraulic characteristics and terrain changes qualitatively in agreement with laboratory data. The modeling study is of practical importance for implementation of engineering countermeasures in the Yellow River, such as breach blocking and head wrapping. [ABSTRACT FROM AUTHOR]

Approximately 90% of the sediment yield of the Yellow River is derived from the Loess Plateau. In this paper, the Loess Plateau was used as the research object. To investigate the influence of economic and social development on reducing sediment load of the Yellow River, a mathematical method was employed with hydrological and sediment data from three hydrological stations (Toudaoguai and Sanmenxia at the Yellow River, and Ganguyi at the Yan River) as well as per capita GDP data from the Yan River basin. The results showed that the reduction in runoff in the reaches between the Toudaoguai and Sanmenxia stations accounted for 39.3% of the decrease in the sediment load of the Yellow River, and the other 60.7% of the decrease may have resulted from economic and social development. Using the Yan River basin as an example, there was an inverse relationship between per capita GDP and sediment delivery during the period from 1984 to 2018. Grey relational analysis revealed a relatively high relation between the sediment load of the Yan River and the number of rural laborers transferred from the area, the afforestation area, and the tertiary industry value of Yan'an city. Thus, economic development and social transformation are highly related to sediment delivery in the basin, which may result in a decrease in sediment delivery to some extent. [ABSTRACT FROM AUTHOR]

Understanding the formation of the Qilian Shan in the NE Tibetan Plateau provides insights into the growth mechanisms of the northern portion of the plateau through time. The onset time of exhumation in the Qilian Shan is still debated. The Qinghai Nan Shan subrange, located in the southeastern Qilian Shan, is cut by the Yellow River that forms Longyang Gorge, providing a good vertical profile for thermochronological investigation of exhumation. In this paper, we reconstruct the cooling and exhumation history of the Eastern Qinghai Nan Shan using apatite fission-track(AFT) and apatite (U Th)/He(AHe) thermochronological dating on basement rocks. The fission-track data display a marked age-elevation trend from Early Cretaceous (114–122 Ma) ages at the bottom of the canyon to Early-Middle Jurassic ages (165–180 Ma) at the top. Mean (U Th)/He ages are mainly Early Cretaceous (97–128 Ma) with one Eocene outlier (42 Ma). Combined with fission track lengths, D par values and thermal modeling results, these data indicate that the study area resided above the closure temperature of AFT and AHe until Early Cretaceous. Rapid cooling occurred during the Early Cretaceous and early Cenozoic likely driven by the Lhasa and Indian blocks collision with the southern margin of the Asian continent. Nonetheless, since then exhumation was limited to less than a few kilometers in the study area. Combined with regional geological studies, the thermochronological analysis demonstrates that, since the Mesozoic, intense exhumation occurred simultaneously along the northern and southern margins of the Qilian Shan. Hence, we suggest that the geomorphic framework of the northeast margin of the Tibetan Plateau was established during the Early Cretaceous-early Cenozoic. • Low-temperature thermochronological study was carried out for Yellow River valley. • Eastern Qinghai Nan Shan experienced rapid exhumation since the late Mesozoic. • Geomorphic framework of the NE Tibetan Plateau was initially established since the late Mesozoic. [ABSTRACT FROM AUTHOR]

In order to determine the key influencing factors, risk areas, and source pathways of heavy metals in the sediment of the Yellow River, 37 samples were collected in the surface sediment (0–5 cm) of the Inner Mongolia section of the Yellow River main stream for the determination of heavy metals copper (Cu), nickel (Ni), zinc (Zn), chromium (Cr), lead (Pb), and cadmium (Cd). Based on the geographical detector model (GDM) and ArcGIS 10.2 software, this paper selected 6 heavy metals and 15 influencing factors, including 8 natural factors and 7 anthropogenic factors, to detect key influencing factors, risk areas, and sources of heavy metals. The results showed that: (1) The average contents of heavy metals Cr and Cd in the sediments exceeded the average value in soil, the world average concentration in the shales, and the first-level standard of soil environmental quality in China, and they were the main risk metals; (2) Vegetation coverage (VC) was the largest influencing factor for the spatial distribution of heavy metals in the sediment, followed by per capita income (PI), and land use type (LUT) and road network density (RD) were smaller influencing factors. The interactions of the factors were enhanced; (3) The Wuhai section for a risk area was mainly polluted by Cd and Pb, which were caused by atmospheric deposition and industrial emission. The Baotou section for a risk area was mainly polluted by Cr, which mainly originated from river transportation and industrial discharge. The conclusions can provide a scientific basis for the environmental protection and management of the different areas in the Inner Mongolia section of the Yellow River. [ABSTRACT FROM AUTHOR]

Abstract: This paper is to highlight the threatening of climate change on the water shortage problem in North China, a semi-arid and arid area. Observations show that the runoff of the major rivers is decreasing dramatically especially in the lower reaches where water ishighly demanded. Most noticeable are the dry-outs of the Yellow River, the so-called ‘mother river of China’.Water scarcity would be the most front challenge for the society and economy in China, especially the urban area with extremely high population density. The government already paid attention to the deepening of the underground water level at Beijing. Sustainable water resource management should the top priority for the local community to adapt to climate change. Studies show that human activities heavily impact on the local climate and environment in China and a dramatics amount of clean water is wasted or polluted. [Copyright &y& Elsevier]

Many studies indicate the Hetao Basin in Inner Mongolia, northern China, controlled the erosion base level of the upper Yellow River before 1.5 Ma. The late Cenozoic extensional rifting in the Hetao Basin in response to the northeastward growth of the Tibetan Plateau may be an plausible mechanism that initiated the headward erosional signal along the Yellow River at the northeastern margin of Tibetan Plateau ~1.8 Ma ago. However, little attention has been paid to establish the relationship between the late Cenozoic tectonic evolution in the Hetao Basin and integration of the upper Yellow River. In this paper, we explore the tectonic mechanism that can drive headward erosion along the Yellow River and the timescales over which it occurred by reconstructing the late Cenozoic tectonic history in the Hetao Basin. We applied linear inversion of bedrock channel profiles and late Cenozoic sedimentary strata in the Daqing Shan to explore the late Cenozoic tectonic evolution in the Hetao Basin. Results show that the accelerated vertical slip between the Daqing Shan and the Hetao Basin initiated at 2.8 ± 0.8 Ma, and the average relative uplift rate was 0.18 ± 0.04 mm/yr since 2.8 Ma. The lowering of erosion base level in the Hetao Basin since 2.8 ± 0.8 Ma produced a headward erosional signal along the Yellow River that initiated fluvial incision at the northeastern margin of the Tibetan Plateau ~1.8 Ma ago. That indicates the accelerated extensional rifting in the Hetao Basin has been responsible for the integration of the upper Yellow River since the late Pliocene. Our study improved understanding how the Yellow River responds to the late Cenozoic rifting around the Ordos Block, as well as the northeastward growth of the Tibetan Plateau. Meanwhile, these tectonic processes were also linked together by the Yellow River evolution. • Rapid relative uplift between Hetao Basin and Daqing Shan started at 2.8 ± 0.8 Ma. • The average relative uplift rate is 0.18 ± 0.04 mm/yr since 2.8 Ma. • Rifting in Hetao Basin since 2.8 ± 0.8 Ma triggered integration of Yellow River. [ABSTRACT FROM AUTHOR]

Fracture mechanics provide a reliable approach for describing the transformation of intact ice material into broken and fragmented ice by crack growth. In this work, fracture toughness experiments of natural Yellow River ice were performed with a Brazilian disk method. Physical test results showed that the Brazilian disk test method can be used to determine the fracture toughness and tensile strength of Yellow River ice. With the strain rate increased, the fracture toughness tended to decrease. As the temperature decreased, the fracture toughness tended to increase. In addition, the tensile strength under different temperatures and strain rates was analyzed. The obtained material parameters of Yellow River ice can be used to estimate the fracture strength of Yellow River ice. • The paper shows that the Brazil disk test method can be used to determine the fracture toughness of the Yellow River ice. • The fracture toughness of ice increase with the decrease of temperature in a certain range (−3 °C ~ −15 °C). • The fracture toughness of ice decrease with the increase of strain rate in a certain range (10−5 s−1–10−1 s−1). • As the temperature decreasing, the tensile strength increases as a whole, but this trend is not evident (−3 °C ~ −15 °C). • The tensile strength tends to decrease evidently with the strain rate increasing. (10−5 s−1–10−1 s−1). [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to develop a statistical-based model to forecast future domestic water demand in the context of climate change, population growth and technological development in Yellow River. Design/methodology/approach – The model is developed through the analysis of the effects of climate variables and population on domestic water use in eight sub-basins of the Yellow River. The model is then used to forecast water demand under different environment change scenarios. Findings – The model projected an increase in domestic water demand in the Yellow River basin in the range of 67.85 × 10 8 to 62.20 × 10 8 m 3 in year 2020 and between 73.32 × 10 8 and 89.27 × 10 8 m 3 in year 2030. The general circulation model Beijing Normal University-Earth System Model (BNU-ESM) predicted the highest increase in water demand in both 2020 and 2030, while Centre National de Recherches Meteorologiques Climate Model v.5 (CNRM-CM5) and Model for Interdisciplinary Research on Climate- Earth System (MIROC-ESM) projected the lowest increase in demand in 2020 and 2030, respectively. The fastest growth in water demand is found in the region where water demand is already very high, which may cause serious water shortage and conflicts among water users. Originality/value – The simple regression-based domestic water demand model proposed in the study can be used for rapid evaluation of possible changes in domestic water demand due to environmental changes to aid in adaptation and mitigation planning.

In order to determine the key influencing factors, risk areas, and source pathways of heavy metals in the sediment of the Yellow River, 37 samples were collected in the surface sediment (0–5 cm) of the Inner Mongolia section of the Yellow River main stream for the determination of heavy metals copper (Cu), nickel (Ni), zinc (Zn), chromium (Cr), lead (Pb), and cadmium (Cd). Based on the geographical detector model (GDM) and ArcGIS 10.2 software, this paper selected 6 heavy metals and 15 influencing factors, including 8 natural factors and 7 anthropogenic factors, to detect key influencing factors, risk areas, and sources of heavy metals. The results showed that: (1) The average contents of heavy metals Cr and Cd in the sediments exceeded the average value in soil, the world average concentration in the shales, and the first-level standard of soil environmental quality in China, and they were the main risk metals; (2) Vegetation coverage (VC) was the largest influencing factor for the spatial distribution of heavy metals in the sediment, followed by per capita income (PI), and land use type (LUT) and road network density (RD) were smaller influencing factors. The interactions of the factors were enhanced; (3) The Wuhai section for a risk area was mainly polluted by Cd and Pb, which were caused by atmospheric deposition and industrial emission. The Baotou section for a risk area was mainly polluted by Cr, which mainly originated from river transportation and industrial discharge. The conclusions can provide a scientific basis for the environmental protection and management of the different areas in the Inner Mongolia section of the Yellow River.

Streamflow and sediment runoff are important indicators for the changes in hydrological processes. In the context of environmental changes, decreases in both streamflow and sediment (especially in the flood season) are often observed in most of the tributaries of the middle Yellow River in China's Loess Plateau. Understanding the effect of human activities could be useful for the management of soil and water conservation (SWC) and new constructions. In this paper, changes in streamflow and sediment during the flood season (June–September) of the 1966–2017 period in a typical loess hill and gully landform basin were analyzed. Basin-wide rainfall of the flood season decreased nonsignificantly with an average rate of −0.6 mm/flood season for the whole study period by using the trend-free pre-whitening based Mann–Kendall trend test, while the decreasing rate was weakened on the time scale. A remarkable warming trend (1985–1999) and two decreasing trends (1966–1984 and 2000–2017) were observed, and the overall increasing trend could be found in air temperature series with a rate of 0.01 °C/flood season during the study period. Statistical models were developed to describe the rainfall-runoff and rainfall-sediment processes in the pre-impact period (when the hydrological series was stationary). Furthermore, the relative effects of climate variability and human activities on hydrological changes were quantified. Results proved the dominant role of human activities (versus climate variability) on the reductions of both streamflow and sediment load. The relative contribution of human activities to streamflow decrease was 84.6% during the post-impact period 1995–2017, while the contributions were 48.8% and 80.1% for two post-impact periods (1982–1996 and 1997–2017), respectively, to the reduction of sediment load. Besides, the effect of the exclusion of anomalous streamflow or sediment events on change-point detection was also analyzed. It indicated that the anomalous events affect the detection of change points and should be given full consideration in order to decide whether to remove them in the change-point detection. Otherwise, the full series with anomalous samples will completely affect the attribution results of hydrological changes. We also suggest that large-scale SWC measures with different construction quality and operational life could intercept and relieve most floods and high sediment concentration processes, but may amplify the peaks of streamflow and sediment when the interception capacities are exceeded under the condition of extreme rainstorm events. [ABSTRACT FROM AUTHOR]

Streamflow and sediment runoff are important indicators for the changes in hydrological processes. In the context of environmental changes, decreases in both streamflow and sediment (especially in the flood season) are often observed in most of the tributaries of the middle Yellow River in China’s Loess Plateau. Understanding the effect of human activities could be useful for the management of soil and water conservation (SWC) and new constructions. In this paper, changes in streamflow and sediment during the flood season (June−September) of the 1966−2017 period in a typical loess hill and gully landform basin were analyzed. Basin-wide rainfall of the flood season decreased nonsignificantly with an average rate of −0.6 mm/flood season for the whole study period by using the trend-free pre-whitening based Mann−Kendall trend test, while the decreasing rate was weakened on the time scale. A remarkable warming trend (1985−1999) and two decreasing trends (1966−1984 and 2000−2017) were observed, and the overall increasing trend could be found in air temperature series with a rate of 0.01 °C/flood season during the study period. Statistical models were developed to describe the rainfall-runoff and rainfall-sediment processes in the pre-impact period (when the hydrological series was stationary). Furthermore, the relative effects of climate variability and human activities on hydrological changes were quantified. Results proved the dominant role of human activities (versus climate variability) on the reductions of both streamflow and sediment load. The relative contribution of human activities to streamflow decrease was 84.6% during the post-impact period 1995−2017, while the contributions were 48.8% and 80.1% for two post-impact periods (1982−1996 and 1997−2017), respectively, to the reduction of sediment load. Besides, the effect of the exclusion of anomalous streamflow or sediment events on change-point detection was also analyzed. It indicated that the anomalous events affect the detection of change points and should be given full consideration in order to decide whether to remove them in the change-point detection. Otherwise, the full series with anomalous samples will completely affect the attribution results of hydrological changes. We also suggest that large-scale SWC measures with different construction quality and operational life could intercept and relieve most floods and high sediment concentration processes, but may amplify the peaks of streamflow and sediment when the interception capacities are exceeded under the condition of extreme rainstorm events.