Temporal trends of hydro‐climatic variables and runoff response to climatic variability and vegetation changes in the Yiluo River basin,China

The Yiluo River is the largest tributary for the middle and lower reaches of the Yellow River below Sanmenxia Dam. Changes of the hydrological processes in the Yiluo River basin, influenced by the climatic variability and human activities, can directly affect ecological integrity in the lower reach of the Yellow River. Understanding the impact of the climatic variability and human activities on the hydrological processes in the Yiluo River basin is especially important to maintain the ecosystem integrity and sustain the society development in the lower reach of the Yellow River basin. In this study, the temporal trends of annual precipitation, air temperature, reference evapotranspiration (ET₀) and runoff during 1961–2000 in the Yiluo River basin were explored by the Mann‐Kendall method (M‐K method), Yamamoto method and linear fitted model. The impacts of the climatic variability and vegetation changes on the annual runoff were discussed by the empirical model and simple water balance model and their contribution to change of annual runoff have been estimated. Results indicated that (i) significant upwards trend for air temperature and significant downwards trend both for precipitation and ET₀ were detected by the M‐K method at 95% confidence level. And the consistent trends were obtained by the linear fitted model; (ii) the abrupt change started from 1987 detected by the M‐K method and Yamamoto method, and so the annual runoff during 1961–2000 was divided into two periods: baseline period (1961–1986) and changeable period (1987–2000); and (iii) the vegetation changes were the main cause for change of annual runoff from baseline period to changeable period, and climatic variability contributed a little to the change of annual runoff of the Yiluo River. Copyright © 2009 John Wiley & Sons, Ltd.     

Evapotranspiration in the Mekong and Yellow river basins / Evapotranspiration dans les bassins du Mekong et du Fleuve Jaune

Abstract

Estimates of potential evapotranspiration (PET) and reference evapotranspiration (RET) were compared over the Mekong and Yellow river basins, representing humid and semi-arid Asian monsoon regions. Multiple regression relationships between monthly RET, PET, LAI (leaf area index) and climatic variables were explored for different vegetation types. Over the Mekong River basin, the spatial average of RET is only 1.7% lower than PET; however, RET is 140% higher than PET over parts of the Tibetan Plateau, due to the short and sparse grassland, and 30% lower than PET in parts of the lower basin due to the tall and well-developed forests. Over the Yellow River basin, RET is estimated to be higher than PET, on average about 50% higher across the whole basin, due to the generally sparse vegetation. A close linear relationship between annual RET and PET allows the establishment of a regional regression to predict monthly PET from monthly RET, climatic variables and/or vegetation LAI. However, the large prediction errors indicate that the Shuttleworth-Wallace (S-W) model, although it is more complex, should be recommended due to its more robust physical basis and because it successfully accounts for the effect of changing land surface conditions on PET. The limited available field data suggest that the S-W estimate may be more realistic. It was also found that vegetation conditions in summer are primarily controlled by the regional antecedent precipitation in the cold and dry seasons over the Loess Plateau in the middle reaches of the Yellow River.     

Comparison of evapotranspiration variations between the Yellow River and Pearl River basin, China

Based on daily meteorological data at 43 gauging stations in the Pearl River basin and 65 gauging stations in the Yellow River basin, we analyze changing properties of actual evapotranspiration (ET_a), reference evapotranspiration (ET_ref) and precipitation in these two river basins. In our study, Pearl River basin is taken as the ‘energy-limited’ system and the Yellow River basin as the ‘water-limited’ system. The results indicate decreasing ET_a in the Pearl River and Yellow River basin. However, different changing properties are detected for ET_ref when compared to ET_a. The middle and upper Yellow River basin are characterized by increasing ET_ref values, whereas the Pearl River basin is dominated by decreasing ET_ref values. This result demonstrates enhancing drying force in the Yellow River basin. ET_a depends mainly on the changes of precipitation amount in the Yellow River basin. In the Pearl River basin, however, ET_a changes are similar to those of ET_ref, i.e. both are in decreasing trend and which may imply weakening hydrological cycle in the Pearl River basin. Different influencing factors are identified behind the ET_a and ET_ref in the Pearl River and Yellow River basin: In the Pearl River basin, intensifying urbanization and increasing aerosol may contribute much to the evapotranspiration changes. Variations of precipitation amount may largely impact the spatial and temporal patterns of ET_a in the Yellow River basin. The current study is practically and scientifically significant for regional assessment of water resource in the arid and humid regions of China under the changing climate.     

Long‐term trend analysis for major climate variables in the Yellow River basin*

Some previous studies have shown that drying‐up of the lower Yellow River resulted from decreasing precipitation and excessive industrial and agricultural consumption of water from the middle and downstream regions of the Yellow River. On the basis of average air temperature, precipitation, and pan evaporation data from nearly 80 gauging stations in the Yellow River basin, the monotonic trends of major climate variables over the past several decades are analysed. The analysis was mainly made for 12 months and the annual means. The isograms for annual and typical months are given in the paper. The result shows that the average temperature in the study area exhibits an increasing trend, mainly because of the increase of temperature in December, January and February. The largest trend is shown in December and the smallest is in August. There are 65 of 77 stations exhibiting a downward trend for annual precipitation. In all seasons except summer, there is a similar trend in the upstream region of the Yellow River, south of latitude 35°N. It is interesting to note that the pan evaporation has decreased in most areas of the Yellow River basin during the past several decades. April and July showed the greatest magnitude of slope, and the area from Sanmenxia to Huayuankou as well as the Yiluo River basin exhibited the strongest declining trend. The conclusion is that the decreasing pan evaporation results from complex changes of air temperature, relative humidity, solar radiation, and wind speed, and both climate change and human activities have affected the flow regime of the Yellow River during the past several decades. Copyright © 2007 John Wiley & Sons, Ltd.     

黄河径流量的历史演变规律及成因

基于黄河上、中和下游的径流及气候资料，对径流的年代际变化规律及与气候变化的关系进行了分析.结果表明：黄河流域的径流均存在显著的年代际变化趋势，径流的显著特征是从20世纪80年代开始的减少趋势，但并未达到历史的最低，径流减少的趋势在下游比上游更显著，而这种变化趋势与流域的气候变化趋势基本一致，说明在年代际尺度上，径流的变化主要受气候的控制；在不同季节，这种关系有明显差异，如在冬季两者的变化趋势有较大差异.分析还发现，近年来流域地表的干化是流域径流减少的原因，气温的升高更加剧了流域地表干化.     

Factors controlling sediment yield in China's Loess Plateau

The Loess Plateau in China, an area with some of the highest sediment yield in the world, contributes predominant proportion of the sediments found in the Yellow River. We examined sediment yield and its control variables in the plateau based on a multi‐year dataset from 180 gauging stations in areas varying in size from 10² to 10⁴ km². Various morphometric, hydrologic, climatic and land cover variables were estimated in order to understand and predict the variations in sediment yield. The results show a spatial pattern of sediment yield exhibiting an obvious zonal distribution and a coupling between precipitation and vegetation cover that fits the Langbein–Schumm law. A critical threshold of precipitation and vegetation cover was observed among the relationships of sediment yield and precipitation/vegetation cover. A multiple regression equation with three control variables, i.e. vegetation cover, percentage of cultivated loess and annual runoff, explains 65% of the total variation in sediment yield. For the loess dominated basins, where the cultivated loess accounts for more than 60% of the total area, annual runoff was the dominant variable, explaining 76% of the observed variation in sediment yield. The established equation could be a valuable tool for predicting total sediment yield in the Loess Plateau. Copyright © 2010 John Wiley & Sons, Ltd.     

Physically based simulation of the streamflow decrease caused by sediment‐trapping dams in the middle Yellow River

As a result of climate change/variation and its aggravation by human activities over the past several decades, the hydrological conditions in the middle Yellow River in China have dramatically changed, which has led to a sharp decrease of streamflow and the drying up of certain tributaries. This paper simulated and analysed the impact of sediment‐trapping dams (STDs, a type of large‐sized check dam used to prevent sediment from entering the Yellow River main stem) on hydrological processes, and the study area was located in the 3246 km² Huangfuchuan River basin. Changes in the hydrological processes were analysed, and periods of natural and disturbed states were defined. Subsequently, the number and distribution of the STDs were determined based on data collected from statistical reports and identified from remote sensing images, and the topological relationships between the STDs and high‐resolution river reaches were established. A hydrological model, the digital Yellow River integrated model, was used to simulate the STD impact on the hydrological processes, and the maximum STD impact was evaluated through a comparison between the simulation results with and without the STDs, which revealed that the interception effect of the STDs contributed to the decrease of the streamflow by approximately 39%. This paper also analysed the relationship between the spatial distribution of the STDs and rainfall in the Huangfuchuan River basin and revealed that future soil and water conservation measures should focus on areas with a higher average annual rainfall and higher number of rainstorm hours. © 2015 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.     

The 1800-year variation of the lower Yellow River bank breachings in relation to the drainage basin vegetation reconstructed using cave stalagmite records

Rivers are closely related to climate, and the hydrogeomorphic features and stability of river channels respond sensitively to climatic change. However, the history of instrumental observations of climatic, hydrological and channel changes is short, notably limiting our ability to understand the complex river responses to long-term climate change and human activity. In this study, we show that cave stalagmite records reflected the variations in precipitation and temperature in the Yellow River basin, and the net primary productivity (NPP) of vegetation over the past 1800 years can therefore be reconstructed. We found that the reconstructed annual mean precipitation (P_m) and NPP closely related to the 1800-year variation of the lower Yellow River (LYR) channel instability indexed by the frequency of the LYR levee breaching events (LBEs) (F_b) derived from historical documents. The temporal variations in P_m, NPP and F_b exhibited an anti-phase relationship (negative correlation) and in-phase relationship (positive correlation), referred to as Type I and Type II relationships, respectively. The two types alternately appeared, dividing the studied period into several sub-periods. Type I occurred when the vegetation remained in a quasi-natural condition, and Type II occurred when the vegetation had been altered by humans to some degree. These features reflect complex river behaviours in response to climate change and human activity and may be explained by the interaction between climate, vegetation and human activity on the millennial timescale. © 2018 John Wiley & Sons, Ltd.     

Spatiotemporal variations of vegetation cover on the Chinese Loess Plateau(1981―2006):Impacts of climate changes and human activities

Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981-2006 have been investigated using GIMMS and SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed a continued increasing phase during 1981―1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations during 1990―1998; (3) vegetation cover declined rapidly during 1999―2001; and (4) vegetation cover increased rapidly during 2002―2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth. The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led to some beneficial effect in ecology.     

全球变化与植被

本文讨论了全球变化与植被的相互依赖与制约关系，以黄土高原为例，研究了古气候与植被之间的关系以及青藏高原隆升对黄河流域生态环境的改造，分析了人类活动对被的破坏给黄土高原生态系统的影响，提出了植被差异与变迁是引起气候快速和区域变化的主要原因。     

Quantitative assessment of the impact of climate variability and human activities on runoff changes: a case study in four catchments of the Haihe River basin,China

Quantitative evaluation of the effect of climate variability and human activities on runoff is of great importance for water resources planning and management in terms of maintaining the ecosystem integrity and sustaining the society development. In this paper, hydro‐climatic data from four catchments (i.e. Luanhe River catchment, Chaohe River catchment, Hutuo River catchment and Zhanghe River catchment) in the Haihe River basin from 1957 to 2000 were used to quantitatively attribute the hydrological response (i.e. runoff) to climate change and human activities separately. To separate the attributes, the temporal trends of annual precipitation, potential evapotranspiration (PET) and runoff during 1957–2000 were first explored by the Mann–Kendall test. Despite that only Hutuo River catchment was dominated by a significant negative trend in annual precipitation, all four catchments presented significant negative trend in annual runoff varying from ?0.859 (Chaohe River) to ?1.996 mm a^?1 (Zhanghe River). Change points in 1977 and 1979 are detected by precipitation–runoff double cumulative curves method and Pettitt's test for Zhanghe River and the other three rivers, respectively, and are adopted to divide data set into two study periods as the pre‐change period and post‐change period. Three methods including hydrological model method, hydrological sensitivity analysis method and climate elasticity method were calibrated with the hydro‐climatic data during the pre‐change period. Then, hydrological runoff response to climate variability and human activities was quantitatively evaluated with the help of the three methods and based on the assumption that climate and human activities are the only drivers for streamflow and are independent of each other. Similar estimates of anthropogenic and climatic effects on runoff for catchments considered can be obtained from the three methods. We found that human activities were the main driving factors for the decline in annual runoff in Luanhe River catchment, Chaohe River catchment and Zhanghe River catchment, accounting for over 50% of runoff reduction. However, climate variability should be responsible for the decrease in annual runoff in the Hutuo River catchment. Copyright © 2012 John Wiley & Sons, Ltd.     

Changes in daily temperature and precipitation extremes in the Yellow River Basin, China

Spatiotemporal changes in climatic extremes in the Yellow River Basin from 1959 to 2008 were investigated on the basis of a suite of 27 climatic indices derived from daily temperature and precipitation data from 75 meteorological stations with the help of the Mann–Kendall test, linear regression method and GIS technique. Furthermore, the changes in the probability distribution of the extreme indices were examined. The results indicate: (1) The whole basin is dominated by significant increase in the frequency of warm days and warm nights, and dominated by significant decrease in the frequency of cold days and cold nights. Although trends in absolute temperature indices show less spatial coherence compared with that in the percentile-based temperature indices, overall increasing trends can be found in Max Tmax (TXx), Min Tmax (TXn), Max Tmin (TNx) and Min Tmin (TNn). (2) Although the spatial patterns and the number of stations with significant changes for threshold and duration temperature indices are also not identical, general positive trends in warm indices (i.e., summer days (SU25), tropical nights (TR20), warm spell duration indicator and growing season length) and negative trends in cold indices (i.e., frost days, ice days and cold spell duration indicator) can be found in the basin. Annual nighttime temperature has increased at a faster rate than that in daytime temperature, leading to obvious decrease in diurnal temperature range. (3) The changes in precipitation indices are much weaker and less spatially coherent compared with these of temperature indices. For all precipitation indices, only few stations are characterized by significantly change in extreme precipitation, and their spatial patterns are always characterized by irregular and insignificant positive and negative changes. However, generally, changes in precipitation extremes present drying trends, although most of the changes are insignificant. (4) Results at seasonal scale show that warming trends occur for all seasons, particularly in winter. Different from that in other three seasons, general positive trends in max 1-day precipitation (Rx1DAY) and max 5-day precipitation (Rx5DAY) are found in winter. Analysis of changes in probability distributions of indices for 1959–1983 and 1984–2008 indicate a remarkable shift toward warmer condition and a less pronounced tendency toward drier condition during the past decades. The results can provide beneficial reference to water resource and eco-environment management strategies in the Yellow River Basin for associated policymakers and stakeholders.     

Scaling properties of the runoff variations in the arid and semi-arid regions of China: a case study of the Yellow River basin

We analyzed long daily runoff series at six hydrological stations located along the mainstem Yellow River basin by using power spectra analysis and multifractal detrended fluctuation analysis (MF-DFA) technique with aim to deeply understand the scaling properties of the hydrological series in the Yellow River basin. Research results indicate that: (1) the runoff fluctuations of the Yellow River basin exhibit self-affine fractal behavior and different memory properties at different time scales. Different crossover frequency (1/f) indicates that lower crossover frequency usually corresponds to larger basin area, and vice versa, showing the influences of river size on higher frequency of runoff variations. This may be due to considerable regulations of river channel on the runoff variations in river basin of larger basin size; (2) the runoff fluctuations in the Yellow River basin exhibit short-term memory properties at smaller time scales. Crossover analysis by MF-DFA indicates unchanged annual cycle within the runoff variations, implying dominant influences of climatic changes on changes of runoff amount at longer time scales, e.g. 1 year. Human activities, such as human withdrawal of freshwater and construction of water reservoirs, in different reaches of the Yellow River basin may be responsible for different scaling properties of runoff variations in the Yellow River basin. The results of this study will be helpful for hydrological modeling in different time scales and also for water resource management in the arid and semi-arid regions of China.     

BOOK REVIEWS

Abstract

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.     

Spatiotemporal variations of vegetation cover on the Chinese Loess Plateau (1981–2006): Impacts of climate changes and human activities

Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981–2006 have been investigated using GIMMS and SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed a continued increasing phase during 1981–1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations during 1990–1998; (3) vegetation cover declined rapidly during 1999–2001; and (4) vegetation cover increased rapidly during 2002–2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth. The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led to some beneficial effect in ecology. Supported by the National Natural Science Foundation of China (Grant No. 40671019) and the Knowledge Innovation Project of the Institute of Geographical Sciences and Natural Resources Research of Chinese Academy of Sciences     

Analysis of long‐term water balance in the source area of the Yellow River basin

To analyse the long‐term water balance of the Yellow River basin, a new hydrological model was developed and applied to the source area of the basin. The analysis involved 41 years (1960–2000) of daily observation data from 16 meteorological stations. The model is composed of the following three sub‐models: a heat balance model, a runoff formation model and a river‐routing network model. To understand the heat and water balances more precisely, the original model was modified as follows. First, the land surface was classified into five types (bare, grassland, forest, irrigation area and water surface) using a high‐resolution land‐use map. Potential evaporation was then calculated using land‐surface temperatures estimated by the heat balance model. The maximum evapotranspiration of each land surface was calculated from potential evaporation using functions of the leaf area index (LAI). Finally, actual evapotranspiration was estimated by regulating the maximum evapotranspiration using functions of soil moisture content. The river discharge estimated by the model agreed well with the observed data in most years. However, relatively large errors, which may have been caused by the overestimation of surface flow, appeared in some summer periods. The rapid decrease of river discharge in recent years in the source area of the Yellow River basin depended primarily on the decrease in precipitation. Furthermore, the results suggested that the long‐term water balance in the source area of the Yellow River basin is influenced by land‐use changes. Copyright © 2007 John Wiley & Sons, Ltd.     

Sedimentary records of environmental evolution in the Sanmen Lake Basin and the Yellow River running through the Sanmenxia Gorge eastward into the sea

A series of independent faulted basins developed in the present middle reaches of the Yellow River during late Cenozoic, among which the Sanmen Lake Basin is located in the east edge of the Loess Plateau, a transitional zone between the second and third macromorphological step of China. The thick strata of the Sanmen Group deposited in the large basin. The Sanmen Group is a perfect place for the study on paleoenvironmental change, tectono-climatic cycles as well as the formation and evolution of the Yellow River. In this paper, the paleoenvironmental changes, regional tectonic movement and the evolutionary process of the Sanmen Lake Basin during the past 5 Ma were reconstructed based on the analysis of paleomagnetic stratigraphy, pollen, TOC and carbonate content from the Huangdigou outcrop near the Sanmenxia Reservoir, Pinglu County, Shanxi Province. The sedimentary records from the outcrop indicate that the basin was first formated by fault activity at about 5.4 MaBP, and after the strong tectonic movement at 3.6 MaBP the lake enlarged and the rainfall of summer monsoon increased. There was no great climatic transition near 2.6 MaBP, corresponding to the bottom age of loess in the Loess Plateau. After Olduvai event (about 1.77 MaBP) the Picea and Abies were presented in the sediments, which indicates a colder climate. The tectonic movement at 1.2 MaBP caused the light angular discordance between the upper and lower Sanmen Group. The sedimentary records show a cold and wet climate during the prosperous periods of loess accumulation such as L15, L9, L6. The tectonic intensification periods of the Sanmen Basin correspond with the tectonic movements in the Qinghai-Xizang Plateau chronologically. The earliest age of the outflow from the Paleo-Sanmen Lake or the partly cutting off of the Sanmenxia Gorge was about 0.41- 0.35 MaBP. The age of cutting thoroughly the Sanmenxia Gorge by the Yellow River and the disappearance of the Paleo-Sanmen Lake was about 0.15 MaBP, which symbolized the formation of the present Yellow River and had an important influence on the environmental and morphological evolution in the middle and lower reaches of the Yellow River.     

Estimation of potential evapotranspiration over the Yellow River basin: reference crop evaporation or Shuttleworth–Wallace?

Potential evapotranspiration (PET) is a key input to hydrological models. Its estimation has often been via the Penman–Monteith (P–M) equation, most recently in the form of an estimate of reference evapotranspiration (RET) as recommended by FAO‐56. In this paper the Shuttleworth–Wallace (S–W) model is implemented to estimate PET directly in a form that recognizes vegetation diversity and temporal change without reference to experimental measurements and without calibration. The threshold values of vegetation parameters are drawn from the literature based on the International Geosphere–Biosphere Programme land cover classification. The spatial and temporal variation of the LAI of vegetation is derived from the composite NOAA‐AVHRR normalized difference vegetation index (NDVI) using a method based on the SiB2 model, and the Climate Research Unit database is used to provide the required meteorological data. All these data inputs are publicly and globally available. Consequently, the implementation of the S–W model developed in this study is applicable at the global scale, an essential requirement if it is to be applied in data‐poor or ungauged large basins. A comparison is made between the FAO‐56 method and the S–W model when applied to the Yellow River basin for the whole of the last century. The resulting estimates of RET and PET and their association with vegetation types and leaf area index (LAI) are examined over the whole basin both annual and monthly and at six specific points. The effect of NDVI on the PET estimate is further evaluated by replacing the monthly NDVI product with the 10‐day product. Multiple regression relationships between monthly PET, RET, LAI, and climatic variables are explored for categories of vegetation types. The estimated RET is a good climatic index that adequately reflects the temporal change and spatial distribution of climate over the basin, but the PET estimated using the S–W model not only reflects the changes in climate, but also the vegetation distribution and the development of vegetation in response to climate. Although good statistical relationships can be established between PET, RET and/or climatic variables, applying these relationships likely will result in large errors because of the strong non‐linearity and scatter between the PET and the LAI of vegetation. It is concluded that use of the implementation of the S–W model described in this study results in a physically sound estimate of PET that accounts for changing land surface conditions. Copyright © 2006 John Wiley & Sons, Ltd.     

Run-off affected by climate and anthropogenic changes in a large semi-arid river basin

A rapid reduction in run-off has been observed in the middle reaches of the Yellow River basin in recent decades. Understanding the contributions of climate change and human activities, such as vegetation restoration and water consumption, to surface water resource reduction has become urgent and very important for future regional planning. Here, we use attribution approaches to explore the effects of climate change and human activities on run-off over the past six decades. The results showed that the observed annual run-off at Tongguan station, which is located within the mainstream of the Yellow River, exhibited a significant decreasing trend of −0.69 mm year⁻¹ (p < .01) and varied from −0.28 to −1.46 mm year⁻¹ (p < .01) in the eight selected tributaries from 1960 to 2015. Two relatively abrupt changes in the double mass curves occurred around 1979 and 1999; compared with Period 1 (P1; 1960–1979), the average catchment run-off decreased 32% during Period 2 (P2; 1980–1999) and up to 49% during Period 3 (P3; 2000–2015). We calculated that approximately 29% of the reduction in the run-off during P2 and 18% during P3 were attributed to climate change. Increased surface water consumption resulted in effective run-off reduction, with relative contributions of approximately 27% and 28% during P2 and P3, respectively. With the implementation of the “Grain-for-Green” project, the vegetation coverage rapidly increased from 36% in P1 to 52% in P3 and reduced run-off by 35% during P3. These findings explain the run-off reduction and benefit water resource management in the middle reaches of the Yellow River basin.     

Variation of precipitation for the last 300 years over the middle and lower reaches of the Yellow River

Reconstruction of high-resolution historical climatic series is the key issue for Past Global Changes (PAGES) and Climate Variability and Predictability (CLIVAR), the two core projects of the international research programme on global changes. High-resolu- tion historical climatic data are vital for our under-standing the mechanisms of climatic variability, im-proving climate model, and distinguishing anthropo-genic effects from the natural forcing on climate change[1,2]. China, with co…