Wuding River Basin Research Articles

Spatiotemporal variation in rainfall erosivity on the Chinese Loess Plateau during the period 1956–2008

Water resources and soil erosion are the most important environmental concerns on the Chinese Loess Plateau, where soil erosion and sediment yield are closely related to rainfall erosivity. Daily rainfall data from 60 meteorological stations were used to investigate the spatiotemporal variations in annual rainfall, annual erosive rainfall and annual rainfall erosivity on the Chinese Loess Plateau during the period 1956–2008. The annual rainfall, erosive rainfall and rainfall erosivity decreased over the past five decades, as determined by the Mann–Kendall test. A comparison of the annual averaged rainfall, erosive rainfall and rainfall erosivity from 1980 to 2008 with that from 1956 to 1979 revealed a remarkable spatial difference in the rainfall trends on the Loess Plateau. Regions of the plateau with major decreases in rainfall were primarily in the Hekouzhen-Longmen section of the middle Yellow River, especially in the Wuding River basin, the Fenhe basin and the northern-central Shanxi province, where the annual rainfall and erosive rainfall decreased by more than 10% and the annual rainfall erosivity decreased by more than 15%. The rainfall erosivity also decreased more than the annual rainfall. Because the annual rainfall has decreased significantly on the Chinese Loess Plateau over the past 50 years, it is important to better understand the ecological and hydrological processes affected by this climate change.

Variability of effective discharge for suspended sediment transport in a large semi-arid river basin

The variability of effective discharge is analysed for three geomorphological zones (gullied hilly loess, valley–hill loess and eolian sand) in the Wuding River basin, China, based on mean daily flow discharge and mean daily suspended sediment discharge from 1959 to 1969, a period when human disturbance in this catchment was less intensive. A modified approach to the determination of discharge class intervals is developed, framed in terms of equal arithmetic intervals of the standard deviation S for all the discharges, such as S , 0.75 S , 0.5 S , and 0.25 S . The average flow duration of effective discharge in the river basin ranges primarily from 0.026% to 3.16% in the two loess regions (corresponding to large flood events), and from 18.75% to 91.51% in the eolian sand region (corresponding to low or moderate flows). The average flow duration of effective discharge is significantly influenced by the size of class intervals and by characteristics of the flow and sediment regime. Using the most appropriate class interval of 0.25 S , the average flow duration of effective discharge is about 0.026% in the two loess regions (other than 0.104% at Hengshan), but in the eolian sand region it reaches 24.50% at Yulin and 52.66% at Hanjiamao, respectively. Histograms of suspended sediment transport indicate that there is a bimodal dominant discharge for suspended sediment transport, with one peak in the range of low flows and the other in the range of large floods. Drainage density and specific sediment yields are lower in the eolian sand region, where effective discharge events occur more frequently and suspended sediment concentration is much lower than that carried by events of the same discharge in the loess region. In contrast, drainage density is higher in the two loess regions, where infrequent hyperconcentrated flows generate high specific sediment yields. Effective discharge differs significantly from bankfull discharge across the whole Wuding River basin.

Temporal variation of soil moisture over the Wuding River basin assessed with an eco-hydrological model, in-situ observations and remote sensing

Abstract. The change pattern and trend of soil moisture (SM) in the Wuding River basin, Loess Plateau, China is explored based on the simulated long-term SM data from 1956 to 2004 using an eco-hydrological process-based model, Vegetation Interface Processes model, VIP. In-situ SM observations together with a remotely sensed SM dataset retrieved by the Vienna University of Technology are used to validate the model. In the VIP model, climate-eco-hydrological (CEH) variables such as precipitation, air temperature and runoff observations and also simulated evapotranspiration (ET), leaf area index (LAI), and vegetation production are used to analyze the soil moisture evolution mechanism. The results show that the model is able to capture seasonal SM variations. The seasonal pattern, multi-year variation, standard deviation and coefficient of variation (CV) of SM at the daily, monthly and annual scale are well explained by CEH variables. The annual and inter-annual variability of SM is the lowest compared with that of other CEH variables. The trend analysis shows that SM is in decreasing tendency at α=0.01 level of significance, confirming the Northern Drying phenomenon. This trend can be well explained by the decreasing tendency of precipitation (α=0.1) and increasing tendency of temperature (α=0.01). The decreasing tendency of runoff has higher significance level (α=0.001). Because of SM's decreasing tendency, soil evaporation (ES) is also decreasing (α=0.05). The tendency of net radiation (Rn), evapotranspiration (ET), transpiration (EC), canopy intercept (EI) is not obvious. Net primary productivity (NPP), of which the significance level is lower than α=0.1, and gross primary productivity (GPP) at α=0.01 are in increasing tendency.

Grid-size effects on estimation of evapotranspiration and gross primary production over a large Loess Plateau basin, China

A distributed eco-hydrological model based on soil—vegetation—atmosphere transfer processes is applied to estimate actual evapotranspiration (ET) and gross primary production (GPP) over the Wuding River basin, Loess Plateau, China, based on digital elevation model, vegetation and soil information between 2000 and 2003 over three grid sizes: 250 m, 1 km and 8 km. The spatial patterns of annual ET and GPP are related to precipitation variability and land-use/cover conditions. The grid size is shown to affect the spatial patterns of annual ET and GPP, the effect on GPP being more significant than that on ET. Geostatistical and regression analyses demonstrate that precipitation and vegetation influence the scaling effect of ET and GPP in a complex way. When precipitation is high, the scaling effect of ET is more dependent on precipitation. The scaling effect of ET and GPP from 1-km to 8-km grid size is much larger than that from 250-m to 1-km grid size, showing the 1-km grid size to be a feasible choice for simulation of their spatial patterns. Although the annual GPP is more sensitive to the grid size than annual ET, both daily ET and daily GPP averaged over the whole basin seem to be insensitive to the grid size, illustrating that the coarse grid size can be used to simulate spatially-averaged variables without losing much accuracy.

Assessing the impact of climate variability and human activities on streamflow from the Wuding River basin in China

AbstractLocated in the Loess Plateau of China, the Wuding River basin (30 261 km2) contributes significantly to the total sediment yield in the Yellow River. To reduce sediment yield from the catchment, large‐scale soil conservation measures have been implemented in the last four decades. These included building terraces and sediment‐trapping dams and changing land cover by planting trees and improving pastures. It is important to assess the impact of these measures on the hydrology of the catchment and to provide a scientific basis for future soil conservation planning. The non‐parametric Mann–Kendall–Sneyers rank test was employed to detect trends and changes in annual streamflow for the period of 1961 to 1997. Two methods were used to assess the impact of climate variability on mean annual streamflow. The first is based on a framework describing the sensitivity of annual streamflow to precipitation and potential evaporation, and the second relies on relationships between annual streamflow and precipitation. The two methods produced consistent results. A significant downward trend was found for annual streamflow, and an abrupt change occurred in 1972. The reduction in annual streamflow between 1972 and 1997 was 42% compared with the baseline period (1961–1971). Flood‐season streamflow showed an even greater reduction of 49%. The streamflow regime of the catchment showed a relative reduction of 31% for most percentile flows, except for low flows, which showed a 57% reduction. The soil conservation measures reduced streamflow variability, leading to more uniform streamflow. It was estimated that the soil conservation measures account for 87% of the total reduction in mean annual streamflow in the period of 1972 to 1997, and the reduction due to changes in precipitation and potential evaporation was 13%. Copyright © 2007 John Wiley & Sons, Ltd.

Estimating daily evapotranspiration in Wuding River Basin based on MODIS remote sensing data

Estimating daily evapotranspiration in Wuding River Basin based on MODIS remote sensing data

Investigations into the Effects of Human Activities on the Hydrological Cycle in the Yellow River Basin

The Yellow River is the origin of Chinese Nation. The water shortage problem has become so serious in recent years that the social and economy development of the basin has been greatly affected. Investigation into and study of the effects of human activities on hydrological cycle in the Yellow River Basin has very important value to rational allocation, optimized regulation, and effective protection of water resources in the basin. The research principle and method is the natural-artificial dual evolution mode of hydrological cycle. A quantitative analysis was conducted starting from a typical sub-basin in the middle reach of the Yellow River Basin: the Wuding River Basin. Empirical hydrological cycle formulae for the Wuding River are tested to reflect dynamic variation of basin vegetation/land cover. A trend of non-linearity of hydrological cycle in the Wuding River is observed. The principle of the natural-artificial dual evolution mode of hydrological cycle was then applied in the whole Yellow River Basin. The reason for the variation of the hydrological cycle is investigated under natural-artificial driving forces. Results show that natural force takes a main role in evolution of hydro-logical cycle in the source region of the Yellow River Basin. Then as the Yellow River flows downstream, artificial driving forces by human activities such as reservoirs, water and soil conservation measures, and water withdrawal and diversion become more and more important in the evolution of hydrological cycle. The method of nonlinear correction to hydrological cycle is introduced and applied in the Yellow River Basin.

Theory and practice of runoff space-time distribution

Based on the domestic and foreign concerning researches, this paper submits the runoff space-time distribution theory which shows evident scientific significances and powerful practical functions. On the basis of digital basin unit cell deriving from the digital elevation model (DEM) and assumption of linear confluence, this theory has been applied successfully to the runoff correlation researches in humid regions. In order to prove the adaptability of the theory in arid and semi-drought regions, this paper is used to the runoff correlation an alysis in Wuding River basin—a tributary of Yellow River Basin, and has gained preliminary effective verification.

Theory of annual runoff evolution under�natural-artificial dual mode and case study of Wuding River basin on the middle Yellow River

Water cycling process in a river basin becomes more complicated because of the intensified impact by human activities. Study of the law of annual runoff, evolution in a river basin is of great significance to quantitative analysis of the water resources condition in varied environment and prediction of the law of the water resources evolution in the future because year-based time span may best reflect the law of the water resources evolution driven by the nature and human activities in the river basin. This paper advances the theory of annual runoff evolution under natural-artificial dual mode based on the dual mode of the water resources evolution, and the theory is applied for the Wuding River Basin on the middle Yellow River as a case study. A thorough analysis of the precipitation-runoff relationship is made in the case of dynamic variation of ground surface conditions of the Wuding River basin, and the concept of water-soil conservation index are a that indicates adoption of various measures for water and soil conservation to reflect ground surface conditions. Furthermore, precipitation-runoff empirical model is developed to reflect dynamic variation of the ground surface conditions of the river basin. The study may lay a solid foundation for the integrated theoretical platform of the law of the water resources evolution in the Yellow River basin and the dual model of the evolution.