Guangju Zhao

Temporal Variation of Streamflow, Sediment Load and Their Relationship in the Yellow River Basin, China

Variation of streamflow and sediment load in the Yellow River basin has received considerable attention due to its drastic reduction during the past several decades. This paper presents a detailed investigation on the changes of streamflow and sediment load from 1952 to 2011 using monthly observations at four gauging stations along the Yellow River. The results show significant decreasing trends for both streamflow and sediment load at all four gauging stations over the past 60 years. The wavelet transform demonstrated discontinuous periodicities from 1969 to 1973 and after 1986 due to the construction of large reservoirs and implementation of numerous soil and water conservations practices. The sediment rating curves with the power-law function was applied to investigate the relationship between discharge and sediment load. The results indicate distinct variations of the relationship between streamflow and sediment and implied significant hydro-morphological changes within different periods. The reducing sediment supply from the source region and the increased erosive power of the river are detected at Lanzhou station, while the decrease of the transport capacity at Toudaoguai is caused by severe siltation. Significant changes in the relationship between streamflow and sediment load are found at Huayuankou and Gaocun stations, which are largely induced by evident sediment income and trapping effects of large reservoirs. It is estimated that numerous reservoirs have strongly altered the regime and magnitude of streamflow and trapped large amount of sediment, leading to severe siltation and evident reduction of their total volumes. A decrease in precipitation, incoming water from the upper reaches, soil and water conservation measures as well as water consumption contribute most to the significant reduction of streamflow. The decrease of sediment load mainly resulted from various soil and water conservation measures and trapping in reservoirs from 1986 to 2011.

Changes in sediment discharge in a sediment-rich region of the Yellow River from 1955 to 2010: implications for further soil erosion control

The well-documented decrease in the discharge of sediment into the Yellow River has attracted considerable attention in recent years. The present study analyzed the spatial and temporal variation of sediment yield based on data from 46 hydrological stations in the sediment-rich region of the Yellow River from 1955 to 2010. The results showed that since 1970 sediment yield in the region has clearly decreased at different rates in the 45 sub-areas controlled by hydrological stations. The decrease in sediment yield was closely related to the intensity and extent of soil erosion control measures and rainstorms that occurred in different periods and sub-areas. The average sediment delivery modulus (SDM) in the study area decreased from 7,767.4 t/(km2 ·a) in 1951–1969 to 980.5 t/(km2·a) in 2000–2010. Our study suggested that 65.5% of the study area with the SDM below 1,000 t/(km2·a) is still necessary to control soil deterioration caused by erosion, and soil erosion control measures should be further strengthened in the areas with the SDM above 1,000 t/(km2·a).

Check dam identification using multisource data and their effects on streamflow and sediment load in a Chinese Loess Plateau catchment

Abstract During the recent six decades, numerous check dams have been constructed for soil erosion control and agricultural production, and have become the key measure for soil and water conservation in the Loess Plateau. Obtaining check dam information is very important for soil erosion control and river basin management. This study utilizes remote-sensing images in conjunction with Google Earth images and field survey to derive the spatial distribution of the check dams in the Huangfuchuan catchment. Multisource data including topographic maps, Landsat images, and images from Google Earth are collected for check dam identification. The results are verified based on a field survey. The water surface area of the check dams derives from in situ measurement and images present good relationship with the high correlation coefficient of 0.96. Furthermore, the area extent and number of check dams derived from the remote sensing images are similar to those from Google Earth images. Historically, an increase in the check dam number, controlled area, and storage capacity indicate their substantial trapping effects on streamflow and sediment load in the Huangfuchuan catchment. This study may be a good reference for proposing an efficient approach to identify the check dams and provide decision supports for soil and water conservation in the Loess Plateau.

Loess Landslide Inventory Map Based on GF-1 Satellite Imagery

Rainfall-induced landslides are a major threat in the hilly and gully regions of the Loess Plateau. Landslide mapping via field investigations is challenging and impractical in this complex region because of its numerous gullies. In this paper, an algorithm based on an object-oriented method (OOA) has been developed to recognize loess landslides by combining spectral, textural, and morphometric information with auxiliary topographic parameters based on high-resolution multispectral satellite data (GF-1, 2 m) and a high-precision DEM (5 m). The quality percentage (QP) values were all greater than 0.80, and the kappa indices were all higher than 0.85, indicating good landslide detection with the proposed approach. We quantitatively analyze the spectral, textural, morphometric, and topographic properties of loess landslides. The normalized difference vegetation index (NDVI) is useful for discriminating landslides from vegetation cover and water areas. Morphometric parameters, such as elongation and roundness, can potentially improve the recognition capacity and facilitate the identification of roads. The combination of spectral properties in near-infrared regions, the textural variance from a grey level co-occurrence matrix (GLCM), and topographic elevation data can be used to effectively discriminate terraces and buildings. Furthermore, loess flows are separated from landslides based on topographic position data. This approach shows great potential for quickly producing accurate results for loess landslides that are induced by extreme rainfall events in the hilly and gully regions of the Loess Plateau, which will help decision makers improve landslide risk assessment, reduce the risk from landslide hazards and facilitate the application of more reliable disaster management strategies.

Impacts of Rainfall and Land Use on Sediment Regime in a Semi-Arid Region: Case Study of the Wuqi Catchment in the Upper Beiluo River Basin, China

The middle reaches of the Yellow River Basin transport the vast majority of sediment (>85% of the basins total available sediment load), which has had profound effects on the characteristics of the middle and lower reaches of the Yellow River. With recent land use and land cover change, the Yellow River Basin has experienced significant sediment regime fluctuations. In this study, we analyzed the sediment regime from the Wuqi catchment which feeds into the upper reaches of the Beiluo River. Results show that a significant decreasing trend in annual suspended sediment discharge and suspended sediment concentration has existed from 1985 to 2008. The change-point year (the year that abrupt changes in sediment regime occurred in the catchment) was detected in 2001 (p < 0.05) for suspended sediment discharge and sediment concentration. There was a significant decreasing trend in streamflow discharge with the change-point year detected in 2002. Meanwhile, erosive rainfall and heavy rainfall exhibits an increasing but not significant trend. Coevally, land use has undergone considerable transformation. Compared to rainfall, land use, and land cover change and soil and water conservation have played a major role in influencing the sediment regime post-2000. In order to reduce soil erosion and sediment yield, more attention should be paid to changes in land use pattern and the impacts of soil and water conservation.

Dynamic sediment discharge in the Hekou–Longmen region of Yellow River and soil and water conservation implications

The middle reaches of the Yellow River Basin transport the vast majority of sediment (>85% of the basins total available sediment load), which has had profound effects on the characteristics of the middle and lower reaches of the Yellow River. Since the late 1950s, soil and water conservation measures have been extensively implemented in the Loess Plateau, China, especially since the 1970s. This has resulted in sediment discharge changing significantly. In this study, data from 22 catchments in the region of the Loess Plateau from Hekou to Longmen in the middle reaches of the Yellow River were analyzed to investigate the responses of the sediment regime to climate change and human activities. The non-parametric Mann-Kendall test and the Pettitt test were used to identify trends and shifts in sediment discharge. All 22 catchments had a significantly decreasing trend (P<0.01) in annual sediment discharge. Change point years were detected between 1971 and 1994, and were concentrated between 1978 and 1984 in 17 catchments. Moreover, erosive rainfall exhibited a tendency to decrease, but this was not a significant trend. Compared to rainfall, human activities, primarily soil and water conservation and environmental rehabilitation campaigns, have played a more prominent role in the changes in sediment regimes. In order to reduce soil erosion and sediment yield, more attention should be paid to proper and rational soil and water conservation and eco-restoration in this region.

Water use efficiency of net primary production in global terrestrial ecosystems

The carbon and water cycles of terrestrial ecosystems, which are strongly coupled via water use efficiency (WUE), are influenced by global climate change. To explore the relationship between the carbon and water cycles and predict the effect of climate change on terrestrial ecosystems, it is necessary to study the WUE in global terrestrial ecosystems. In this study, the 13-year WUE (i.e., net primary production (NPP)/evapotranspiration (ET)) of global terrestrial ecosystems was calculated based on the Moderate Resolution Imaging Spectro-radiometer (MODIS) NPP (MOD17A3) and ET (MOD16A3) products from 2000 to 2012. The results indicate that the annual average WUE decreased but not significantly, and the 13-year mean value was 868.88 mg C m −2 mm −1. The variation trend of WUE value for each pixel differed greatly across the terrestrial ecosystems. A significant variation (P<0.05) occurred in about 18.50% of the land surface. WUE was spatially distributed from 0 to 2541 mg C m −2 mm −1, and 58.78% of the WUE values were concentrated in the interval of 600–1200 mg C m −2 mm −1. The WUE increased from north to south in Africa and Oceania and from east to west in Europe and South America. Both latitudinal and longitudinal gradients existed in Asia and North America. The following trends in the WUE of different continents and Köppen–Geiger climates were observed: Europe (1129.71 mg C m −2 mm −1)> Oceania (1084.46 mg C m −2 mm −1)> Africa (893.51 mg C m −2 mm −1)> South America (893.07 mg C m −2 mm −1)> North America (870.79 mg C m −2 mm −1)> Asia (738.98 mg C m −2 mm −1) and warm temperate climates (1094 mg C m −2 mm −1)> snowy climates (862 mg C m −2 mm −1)> arid climates (785 mg C m −2 mm −1)> equatorial climates (732 mg C m −2 mm −1)> polar climates (435 mg C m −2 mm −1). Based on the WUE value and the present or future rainfall, the maximum carbon that fixed in one region may be theoretically calculated. Also, under the background of global climatic change, WUE may be regarded as an important reference for allotting CO 2 emissions offsets and carbon transactions.

Have conservation measures improved Yellow River health

The Yellow River is the second-longest river in China with a length of 5,464 km (3,395 mi). It originates from the eastern Qinghai–Tibet Plateau flows eastward through the Loess Plateau, and empties into the Bohai Sea. The whole river basin, which covers approximately 752,443 km2 (290,520 mi2), was regarded as “the cradle of Chinese Civilization” (Zhu et al. 2004) and has played an important role in regional economic development. However, extreme floods, hyperconcentrated sediment flow, and water shortages have been ongoing environmental problems that the Chinese national government must face and resolve in the Yellow River Basin. The Yellow River is well known worldwide due to its extraordinarily high suspended sediment concentration. The Loess Plateau, located in the upper-middle reaches of the Yellow River, contributed approximately 90% of the sediment in the mainstream. Additionally, catastrophic floods that occurred frequently in the tributaries during summer months brought hyperconcentrated sediment flow to the main stem of the river. Large amounts of sediment deposition have made the Yellow River a “suspended” river in which the channel bottom reaches up to 10 m (33 ft) above ground. The continual elevation of the river bed has resulted in a great decline of sediment transport capacity.

Analysis of streamflow and sediment flux changes in the Yangtze River basin

The present paper focuses on the variation of the annual streamflow and sediment fluxes in the Yangtze River basin from 1956 to 2009 using annual observations at 10 hydrological gauging stations. Both simple linear regression analysis and the Mann-Kendall test are applied to the time series for trend detection, and the relations between streamflow and precipitation and between sediment flux and precipitation are analyzed with the help of a double mass curve function. The results present differing trends of changes in streamflow and sediment.

Effects of climate change and human activities on runoff and sediment inputs of the largest freshwater lake in China, Poyang Lake

ABSTRACT The nonparametric Mann-Kendall test and the Pettitt test were employed to examine the change trends and shifts of runoff and sediment input to Poyang Lake between 1961 and 2013. Water balance and linear regression models were used to evaluate the impacts of climate variability and human activities on the runoff and sediment discharge changes. The results showed that runoff inputs to the lake had insignificant temporal trends and change points, while sediment inputs had significant decreasing trends, with an abrupt change in 1989. Quantitative assessment demonstrated that human activities led to a small decrease (5.5%) in runoff inputs to the lake, and a dramatic (121.4%) decrease in sediment inputs to the lake between the reference period (before the change point) and the human-influenced period (after the change point). This work provides a useful reference for future policy makers in water resource utilization and environmental safety of the Poyang Lake basin.