The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the veg...The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the vegetation growing season(SOS)based on remote sensing data is easily affected by outliers because this data series is short. In this study, we determine that the spring minimum temperature is the most influential factor for SOS. The significant negative linear relationship between the two variables in the region is evaluated using Moderate Resolution Imaging Spectroradiometer–Normalized Difference Vegetation Index data for 2000–13. We then reconstruct the SOS time series based on the temperature data for 1960–2013.The regional mean SOS shows an advancing trend of 1.42 d(10 yr)during 1960–2013, with the SOS occurring on the 160th and 151st days in 1960 and 2013, respectively. The advancing trend enhances to 6.04 d(10 yr)during the past 14 years. The spatiotemporal variations of the reconstructed SOS data are similar to those deduced from remote sensing data during the past 14 years. The latter exhibit an even larger regional mean trend of SOS [7.98 d(10 yr)] during 2000–13. The Arctic Oscillation is found to have significantly influenced the changing SOS, especially for the eastern part of the region,during 2000–13.展开更多
The Three-River Headwaters Region(TRHR) of Qinghai Province, in the Tibetan Plateau of China, is the main source of the Yangtze, Yellow, and Lancang rivers, and is very significant to the security of freshwater resour...The Three-River Headwaters Region(TRHR) of Qinghai Province, in the Tibetan Plateau of China, is the main source of the Yangtze, Yellow, and Lancang rivers, and is very significant to the security of freshwater resources for China and southeastern Asia. It is a critical ecological region of China for its ecological functions, and has been changed or even degraded in recent decades owing to climate change and human pressure. To effectively protect and restore the degraded ecosystems, the Chinese government initiated a series of ecological conservation projects in TRHR. It is essential to quantitatively assess ecosystem changes and their relationship to driving factors for indepth understanding of long-term changes of ecosystems and effects of ecological restoration policies and offer practical insights for ecological restoration. Here, land cover data has been interpreted with the series data of Landsat during 1990–2015. The patterns of different ecosystems and their developing process have been derived from land cover change. The results show that ecosystem types in TRHR include forest, grassland, cropland,wetland, artificial surface and barren land, accounting for 4.51%, 70.80%, 0.15%, 9.47%, 0.16% and 14.90%,respectively. Barren land converted to wetland was the significant ecosystem change from 1990 to 2015. Increases in temperature and precipitation and implementation of ecological rehabilitation helped maintain relatively stable ecosystem patterns. It is necessary to continue ecological projects to improve and/or maintain the ecosystems in TRHR because there is still a risk of land degradation under increasing climate change and human activity.展开更多
Supported by MSS images in the mid and late 1970s,TM images in the early 1990s and TM/ETM images in 2004,grassland degradation in the"Three-River Headwaters"region (TRH region)was interpreted through analysis on R...Supported by MSS images in the mid and late 1970s,TM images in the early 1990s and TM/ETM images in 2004,grassland degradation in the"Three-River Headwaters"region (TRH region)was interpreted through analysis on RS images in two time series,then the spatial and temporal characteristics of grassland degradation in the TRH region were analyzed since the 1970s.The results showed that grassland degradation in the TRH region was a continuous change process which had large affected area and long time scale,and rapidly strengthen phenomenon did not exist in the 1990s as a whole.Grassland degradation pattern in the TRH region took shape initially in the mid and late 1970s.Since the 1970s,this degradation process has taken place continuously,obviously characterizing different rules in different regions.In humid and semi-humid meadow region,grassland firstly fragmentized, then vegetation coverage decreased continuously,and finally"black-soil-patch"degraded grassland was formed.But in semi-arid and arid steppe region,the vegetation coverage decreased continuously,and finally desertification was formed.Because grassland degradation had obviously regional differences in the TRH region,it could be regionalized into 7 zones, and each zone had different characteristics in type,grade,scale and time process of grassland degradation.展开更多
Soil erosion in the Three-River Headwaters Region(TRHR)of the Qinghai-Tibet Plateau in China has a significant impact on local economic development and ecological environment.Vegetation and precipitation are considere...Soil erosion in the Three-River Headwaters Region(TRHR)of the Qinghai-Tibet Plateau in China has a significant impact on local economic development and ecological environment.Vegetation and precipitation are considered to be the main factors for the variation in soil erosion.However,it is a big challenge to analyze the impacts of precipitation and vegetation respectively as well as their combined effects on soil erosion from the pixel scale.To assess the influences of vegetation and precipitation on the variation of soil erosion from 2005 to 2015,we employed the Revised Universal Soil Loss Equation(RUSLE)model to evaluate soil erosion in the TRHR,and then developed a method using the Logarithmic Mean Divisia Index model(LMDI)which can exponentially decompose the influencing factors,to calculate the contribution values of the vegetation cover factor(C factor)and the rainfall erosivity factor(R factor)to the variation of soil erosion from the pixel scale.In general,soil erosion in the TRHR was alleviated from 2005 to 2015,of which about 54.95%of the area where soil erosion decreased was caused by the combined effects of the C factor and the R factor,and 41.31%was caused by the change in the R factor.There were relatively few areas with increased soil erosion modulus,of which 64.10%of the area where soil erosion increased was caused by the change in the C factor,and 23.88%was caused by the combined effects of the C factor and the R factor.Therefore,the combined effects of the C factor and the R factor were regarded as the main driving force for the decrease of soil erosion,while the C factor was the dominant factor for the increase of soil erosion.The area with decreased soil erosion caused by the C factor(12.10×10^3 km^2)was larger than the area with increased soil erosion caused by the C factor(8.30×10^3 km^2),which indicated that vegetation had a positive effect on soil erosion.This study generally put forward a new method for quantitative assessment of the impacts of the influencing factors on soil erosion,and also provided a scientific basis for the regional control of soil erosion.展开更多
Accurate measurements of the associated vegetation phenological dynamics are crucial for understanding the relationship between climate change and terrestrial ecosystems. However, at present, most vegetation phenologi...Accurate measurements of the associated vegetation phenological dynamics are crucial for understanding the relationship between climate change and terrestrial ecosystems. However, at present, most vegetation phenological calculations are based on a single algorithm or method. Because of the spatial, temporal, and ecological complexity of the vegetation growth processes, a single algorithm or method for monitoring all these processes has been indicated to be elusive. Therefore, in this study, from the perspective of plant growth characteristics, we established a method to remotely determine the start of the growth season(SOG) and the end of the growth season(EOG), in which the maximum relative change rate of the normalized difference vegetation index(NDVI) corresponds to the SOG, and the next minimum absolute change rate of the NDVI corresponds to the EOG. Taking the Three-River Headwaters Region in 2000–2013 as an example, we ascertained the spatiotemporal and vertical characteristics of its vegetation phenological changes. Then, in contrast to the actual air temperature data, observed data and other related studies, we found that the SOG and EOG calculated by the proposed method is closer to the time corresponding to the air temperature, and the trends of the SOG and EOG calculated by the proposed method are in good agreement with other relevant studies. Meantime, the error of the SOG between the calculated and observed in this study is smaller than that in other studies.展开更多
The Three-River Headwater Region(TRHR)of China is a typical representative of the alpine environment in the Central Asian plateau and the alpine grassland in the world.Grassland degradation is one of its serious eco-l...The Three-River Headwater Region(TRHR)of China is a typical representative of the alpine environment in the Central Asian plateau and the alpine grassland in the world.Grassland degradation is one of its serious eco-logical problems.The purpose of this study is to quantify the joint impacts of climate and human activities on grassland changes in TRHR after two phases of Ecological Conservation and Construction Project(Ecological Project).Grassland vegetation coverage is selected as an indicator for analyzing grassland changes.We adopt Sen+Mann-Kendall trend analysis,residual trend analysis and correlation analysis methods to analyze the trends in spatial-temporal changes and driving factors of grassland in TRHR from 2000 to 2019.The results show that:(1)The grassland has been mainly restored,and the degraded grassland area only accounts for 1.66%of TRHR.After the implementation of the first phase of the Ecological Project,the percentage of restored grassland area has significantly increased from 8.82%to 24.57%,and slightly decreased during the second phase.(2)The establish-ment of national nature reserves and the implementation of the Ecological Project have changed the situation that“the grassland inside the reserve is worse than that outside the reserve”.(3)Grassland restoration is mainly af-fected by the joint effects of climate and human activities.Nevertheless,grassland degradation is mainly affected by human activities such as overgrazing and grassland reclamation.All of these findings can enrich our under-standing of grassland restoration in TRHR.Artificial measures have certain limitations in promoting grassland restoration.Natural restoration should be considered when human beings strengthen ecological conservation and transform their production and life styles.展开更多
The ecological environment of the Three-River Headwater Region is primitive and unique,and sensitive and complex to external influences.The Three-River Headwater Region is the largest nature reserve in China,and is al...The ecological environment of the Three-River Headwater Region is primitive and unique,and sensitive and complex to external influences.The Three-River Headwater Region is the largest nature reserve in China,and is also a nature reserve with the highest concentration of biodiversity in the world's high-altitude areas,so the protection of ecological diversity in this region is particularly important.Ecological diversity is the material basis on which the entire humanity depends to survive and develop.It not only provides humans with basic needs such as food,energy and materials,and is also extremely important for maintaining ecological balance,regulating the climate and promoting the sustainable development of the region.Studying the topographical heterogeneity of the region is first of all a true grasp of the topography of the region,which has certain guiding significance for people's production and life.In addition,studying the impact of topographical heterogeneity on the climate of the region will help to study the formation and variation of regional climate.展开更多
The three-river source region (TRSR, including Yangtze, Yellow and Lancang rivers), located in the Qinghai-Tibetan Plateau, China, is a typical alpine zone with apparent ecosystem vulnerability and sensitivity. In thi...The three-river source region (TRSR, including Yangtze, Yellow and Lancang rivers), located in the Qinghai-Tibetan Plateau, China, is a typical alpine zone with apparent ecosystem vulnerability and sensitivity. In this paper, we introduced many interdisciplinary factors, such as landscape pattern indices (Shannon diversity index and Shannon evenness index) and extreme climate factors (number of extreme high temperature days, number of extreme low temperature days, and number of extreme precipitation days), to establish a new model for evaluating the spatial patterns of ecosystem vulnerability changes in the TRSR. The change intensity (CI) of ecosystem vulnerability was also analyzed. The results showed that the established evaluation model was effective and the ecosystem vulnerability in the whole study area was intensive. During the study period of 2001–2011, there was a slight degradation in the eco-environmental quality. The Yellow River source region had the best eco-environmental quality, while the Yangtze River source region had the worst one. In addition, the zones dominated by deserts were the most severely deteriorated areas and the eco-environmental quality of the zones occupied by evergreen coniferous forests showed a better change. Furthermore, the larger the change rates of the climate factors (accumulative temperature of ≥10°C and annual average precipitation) are, the more intensive the CI of ecosystem vulnerability is. This study would provide a scientific basis for the eco-environmental protection and restoration in the TRSR.展开更多
As the source of the Yellow River,Yangtze River,and Lancang River,the Three-River Source Region(TRSR)in China is very important to China’s ecological security.In recent decades,TRSR’s ecosystem has degraded because ...As the source of the Yellow River,Yangtze River,and Lancang River,the Three-River Source Region(TRSR)in China is very important to China’s ecological security.In recent decades,TRSR’s ecosystem has degraded because of climate change and human disturbances.Therefore,a range of ecological projects were initiated by Chinese government around 2000 to curb further degradation.Current research shows that the vegetation of the TRSR has been initially restored over the past two decades,but the respective contribution of ecological projects and climate change in vegetation restoration has not been clarified.Here,we used the Moderate Resolution Imaging Spectroradiometer(MODIS)Enhanced Vegetation Index(EVI)to assess the spatial-temporal variations in vegetation and explore the impact of climate and human actions on vegetation in TRSR during 2001–2018.The results showed that about 26.02%of the TRSR had a significant increase in EVI over the 18 yr,with an increasing rate of 0.010/10 yr(P<0.05),and EVI significantly decreased in only 3.23%of the TRSR.Residual trend analysis indicated vegetation restoration was jointly promoted by climate and human actions,and the promotion of human actions was greater compared with that of climate,with relative contributions of 59.07%and40.93%,respectively.However,the degradation of vegetation was mainly caused by human actions,with a relative contribution of71.19%.Partial correlation analysis showed that vegetation was greatly affected by temperature(r=0.62,P<0.05)due to the relatively sufficient moisture but lower temperature in TRSR.Furthermore,the establishment of nature reserves and the implementation of the Ecological Protection and Restoration Program(EPRP)improved vegetation,and the first stage EPRP had a better effect on vegetation restoration than the second stage.Our findings identify the driving factors of vegetation change and lay the foundation for subsequent effective management.展开更多
蒸散发(Evapotranspiration,ET)是陆地水、碳和能量交换的重要组成部分。基于不同模型和不同遥感数据估算的ET,存在不同程度的不确定性。贝叶斯模型平均(Bayesian model averaging,BMA)提供了降低不确定性的一种途径。本研究采用中国三...蒸散发(Evapotranspiration,ET)是陆地水、碳和能量交换的重要组成部分。基于不同模型和不同遥感数据估算的ET,存在不同程度的不确定性。贝叶斯模型平均(Bayesian model averaging,BMA)提供了降低不确定性的一种途径。本研究采用中国三江源地区水热通量观测数据,以ARTS、PT-JPL、MOD16和SSEBop遥感蒸散发产品为基础,进行了BMA集成研究,生成了三江源地区2003–2015年250 m空间分辨率的年均地表蒸散发数据集。通过验证各输入模型和BMA集成模型结果,发现基于BMA的ET与通量观测数据相关性达0.94,能够解释观测数据季节变化的89%,优于单个模型的性能。说明BMA模型集成能够整合不同模型内在优势,降低结果估算的不确定性,从而获得更可靠的估算结果。本数据集可为三江源区域水热变化研究和生态系统调节功能评估提供更精确的数据支持。展开更多
The Three-River Headwaters(TRH)region in the Tibetan Plateau is vulnerable to climate change;changes in summer(June–August)precipitation have a significant impact on water security and sustainability in both local an...The Three-River Headwaters(TRH)region in the Tibetan Plateau is vulnerable to climate change;changes in summer(June–August)precipitation have a significant impact on water security and sustainability in both local and downstream areas.However,the changes in summer precipitation of different intensities over the TRH region,along with their influencing factors,remain unclear.In this study,we used observational and ERA5 reanalysis data and employed a precipitation categorization and water vapor budget analysis to quantify the categorized precipitation variations and investigate their possible linkages with the water vapor budget.Our results showed an increasing trend in summer precipitation at a rate of 0.9 per year(p<0.1)during 1979–2020,with a significant dry-to-wet transition in 2002.The category‘very heavy precipitation’(10 mm d−1)contributed 65.1%of the increased summer precipitation,which occurred frequently in the northern TRH region.The dry-to-wet transition was caused by the effects of varied atmospheric circulations in each subregion.Southwesterly water vapor transport through the southern boundary was responsible for the increased net water vapor flux in the western TRH region(158.2%),while southeasterly water vapor transport through the eastern boundary was responsible for the increased net water vapor flux in the central TRH(155.2%)and eastern TRH(229.2%)regions.Therefore,we inferred that the dry-to-wet transition of summer precipitation and the increased‘very heavy precipitation’over the TRH was caused by increased easterly and southerly water vapor transport.展开更多
The Three-River Headwaters region in China is an ecological barrier providing en- vironmental protection and regional sustainable development for the mid-stream and down- stream areas, which also plays an important ro...The Three-River Headwaters region in China is an ecological barrier providing en- vironmental protection and regional sustainable development for the mid-stream and down- stream areas, which also plays an important role in animal husbandry in China. This study estimated the grassland yield in the Three-River Headwaters region based on MODIS NPP data, and calculated the proper livestock-carrying capacity of the grassland. We analyzed the overgrazing number and its spatial distribution characteristics through data comparison be- tween actual and proper livestock-carrying capacity. The results showed the following: (1) total grassland yield (hay) in the Three-River Headwaters region was 10.96 million tons in 2010 with an average grassland yield of 465.70 kg/hm2 (the spatial distribution presents a decreasing trend from the east and southeast to the west and northwest in turn); (2) the proper livestock-carrying capacity in the Three-River Headwaters region is 12.19 million sheep units (hereafter described as "SU"), and the average stocking capacity is 51.27 SU [the proper carrying capacity is above 100 SU/km2 in the eastern counties, 60 SU/km2 in the cen- tral counties (except Madoi County), and 30 SU/km2 in the western counties]; and (3) total overgrazing number was 6.52 million SU in the Three-River Headwaters region in 2010, with an average overgrazing ratio of 67.88% and an average overgrazing number of 27.43 SU/km2 A higher overgrazing ratio occurred in Tongde, Xinghai, Yushu, Henan and Z^kog. There was no overgrazing in Zhiduo, Tanggula Township and Darlag, Qumerleb and Madoi. The re- mainder of the counties had varying degrees of overgrazing.展开更多
Based on the precipitation and temperature data of the 12 meteorological stations in the "Three-River Headwaters" region and the observed runoff data of Zhimenda in the headwater sub-region of the Yangtze River, Tan...Based on the precipitation and temperature data of the 12 meteorological stations in the "Three-River Headwaters" region and the observed runoff data of Zhimenda in the headwater sub-region of the Yangtze River, Tangnaihai in the headwater sub-region of the Yellow River and Changdu in the headwater sub-region of the Lancang River during the period 1965-2004, this paper analyses the trends of precipitation, temperature, runoff depth and carries out significance tests by means of Mann-KendalI-Sneyers sequential trend test. Mak- kink model is applied to calculate the potential evaporation. The runoff model driven by pre- cipitation and potential evaporation is developed and the influence on runoff by climate change is simulated under different scenarios. Results show that during the period 1965-2004 the temperature of the "Three-River Headwaters" region is increasing, the runoff of the three hydrological stations is decreasing and both of them had abrupt changes in 1994, while no significant trend changes happen to the precipitation. The runoff model suggests that the precipitation has a positive effect on the runoff depth, while the potential evaporation plays a negative role. The influence of the potential evaporation on the runoff depth of the Lancang River is found to be the significant in the three rivers; and that of the Yellow River is the least. The result of the scenarios analysis indicates that although the precipitation and the potential evaporation have positive and negative effects on runoff relatively, fluctuated characteristics of individual effect on the runoff depth in specific situations are represented.展开更多
The Three-River Headwater Region(TRHR), known as the "Water Tower of China", is an important ecological shelter for national security interests and regional sustainable development activities for many downstream r...The Three-River Headwater Region(TRHR), known as the "Water Tower of China", is an important ecological shelter for national security interests and regional sustainable development activities for many downstream regions in China and a number of Southeast Asian countries. The TRHR is a high-elevation, cold environment with a unique, but typical alpine vegetation system. Net primary productivity(NPP) is a key vegetation parameter and ecological indicator that can reflect both natural environmental changes and carbon budget levels. Given the unique geographical environment and strategic location of the TRHR, many scholars have estimated NPP of the TRHR by using different methods; however, these estimates vary greatly for a number of reasons. To date, there is no paper that has reviewed and assessed NPP estimation studies conducted in the TRHR. Therefore, in this paper, we(1) summarized the related methods and results of NPP estimation in the TRHR in a systematic review of previous research;(2) discussed the suitability of existing methods for estimating NPP in the TRHR and highlighted the most significant challenges; and(3) assessed the estimated NPP results. Finally, developmental directions of NPP estimation in the TRHR were prospected.展开更多
Based on a monthly dataset of precipitation time series (1961-2010) from 12 me- teorological stations across the Three-River Headwater Region (THRHR) of Qinghai Province China, the spatio-temporal variation and ab...Based on a monthly dataset of precipitation time series (1961-2010) from 12 me- teorological stations across the Three-River Headwater Region (THRHR) of Qinghai Province China, the spatio-temporal variation and abrupt change analysis of precipitation were exam- ined by using moving average, linear regression, spline interpolation, the Mann-Kendall test and so on. Major conclusions were as follows. (1) The long-term annual and seasonal pre- cipitation in the study area indicated an increasing trend with some oscillations during 1961-2010; however, the summer precipitation in the Lantsang (Lancang) River Headwater Region (LARHR), and the autumn precipitation in the Yangtze River Headwater Region (YERHR) of the THRHR decreased in the same period. (2) The amount of annual precipita- tion in the THRHR and its three sub-headwater regions was greater in the 1980s and 2000s. The springs were fairly wet after the 1970s, while the summers were relatively wet in the 1960s, 1980s and 2000s. In addition, the amount of precipitation in the autumn was greater in the 1970s and 1980s, but it was relatively less for the winter precipitation, except in the 1990s (3) The normal values of spring, summer, winter and annual precipitation in the THRHR and its three sub-headwater regions all increased, but the normal value of summer precipitation in the LARHR had a negative trend and the normal value of winter precipitation declined in general. (4) The spring and winter precipitation increased in most of the THRHR. The summer autumn and annual precipitation increased mainly in the marginal area of the west and north and decreased in the regions of Yushu, Zaduo, Jiuzhi and Banma. (5) The spring and winter precipitation in the THRHR and its three sub-headwater regions showed an abrupt change, except for the spring precipitation in the YARHR. The abrupt changes of spring precipitation were mainly in the late 1980s and early 1990s, while the abrupt changes of winter precipita- tion were primary in the mid- to late 1970s. This research would be helpful for further under- standing the trends and periodicity of precipitation and for watershed-based water resource management in the THRHR.展开更多
基金supported by the National Key Research and Development Program of China(Grant Nos.2016YFA0600400 and 2016YFA0602500)supported by the Open Research Fund of the Key Laboratory of Tibetan Environmental Changes and Land Surface Processes,Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant No.41405082)
文摘The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the vegetation growing season(SOS)based on remote sensing data is easily affected by outliers because this data series is short. In this study, we determine that the spring minimum temperature is the most influential factor for SOS. The significant negative linear relationship between the two variables in the region is evaluated using Moderate Resolution Imaging Spectroradiometer–Normalized Difference Vegetation Index data for 2000–13. We then reconstruct the SOS time series based on the temperature data for 1960–2013.The regional mean SOS shows an advancing trend of 1.42 d(10 yr)during 1960–2013, with the SOS occurring on the 160th and 151st days in 1960 and 2013, respectively. The advancing trend enhances to 6.04 d(10 yr)during the past 14 years. The spatiotemporal variations of the reconstructed SOS data are similar to those deduced from remote sensing data during the past 14 years. The latter exhibit an even larger regional mean trend of SOS [7.98 d(10 yr)] during 2000–13. The Arctic Oscillation is found to have significantly influenced the changing SOS, especially for the eastern part of the region,during 2000–13.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program (Grant No.2019QZKK0608)the National Nature Science Foundation of China (Grant No.41730752 and No.41971277).
文摘The Three-River Headwaters Region(TRHR) of Qinghai Province, in the Tibetan Plateau of China, is the main source of the Yangtze, Yellow, and Lancang rivers, and is very significant to the security of freshwater resources for China and southeastern Asia. It is a critical ecological region of China for its ecological functions, and has been changed or even degraded in recent decades owing to climate change and human pressure. To effectively protect and restore the degraded ecosystems, the Chinese government initiated a series of ecological conservation projects in TRHR. It is essential to quantitatively assess ecosystem changes and their relationship to driving factors for indepth understanding of long-term changes of ecosystems and effects of ecological restoration policies and offer practical insights for ecological restoration. Here, land cover data has been interpreted with the series data of Landsat during 1990–2015. The patterns of different ecosystems and their developing process have been derived from land cover change. The results show that ecosystem types in TRHR include forest, grassland, cropland,wetland, artificial surface and barren land, accounting for 4.51%, 70.80%, 0.15%, 9.47%, 0.16% and 14.90%,respectively. Barren land converted to wetland was the significant ecosystem change from 1990 to 2015. Increases in temperature and precipitation and implementation of ecological rehabilitation helped maintain relatively stable ecosystem patterns. It is necessary to continue ecological projects to improve and/or maintain the ecosystems in TRHR because there is still a risk of land degradation under increasing climate change and human activity.
基金CAS Action-plan for West Development,No.KZCX2-XB2-06-03National Key Project of Scientific andTechnical Supporting Programs,No.2006BAC08B00
文摘Supported by MSS images in the mid and late 1970s,TM images in the early 1990s and TM/ETM images in 2004,grassland degradation in the"Three-River Headwaters"region (TRH region)was interpreted through analysis on RS images in two time series,then the spatial and temporal characteristics of grassland degradation in the TRH region were analyzed since the 1970s.The results showed that grassland degradation in the TRH region was a continuous change process which had large affected area and long time scale,and rapidly strengthen phenomenon did not exist in the 1990s as a whole.Grassland degradation pattern in the TRH region took shape initially in the mid and late 1970s.Since the 1970s,this degradation process has taken place continuously,obviously characterizing different rules in different regions.In humid and semi-humid meadow region,grassland firstly fragmentized, then vegetation coverage decreased continuously,and finally"black-soil-patch"degraded grassland was formed.But in semi-arid and arid steppe region,the vegetation coverage decreased continuously,and finally desertification was formed.Because grassland degradation had obviously regional differences in the TRH region,it could be regionalized into 7 zones, and each zone had different characteristics in type,grade,scale and time process of grassland degradation.
文摘Soil erosion in the Three-River Headwaters Region(TRHR)of the Qinghai-Tibet Plateau in China has a significant impact on local economic development and ecological environment.Vegetation and precipitation are considered to be the main factors for the variation in soil erosion.However,it is a big challenge to analyze the impacts of precipitation and vegetation respectively as well as their combined effects on soil erosion from the pixel scale.To assess the influences of vegetation and precipitation on the variation of soil erosion from 2005 to 2015,we employed the Revised Universal Soil Loss Equation(RUSLE)model to evaluate soil erosion in the TRHR,and then developed a method using the Logarithmic Mean Divisia Index model(LMDI)which can exponentially decompose the influencing factors,to calculate the contribution values of the vegetation cover factor(C factor)and the rainfall erosivity factor(R factor)to the variation of soil erosion from the pixel scale.In general,soil erosion in the TRHR was alleviated from 2005 to 2015,of which about 54.95%of the area where soil erosion decreased was caused by the combined effects of the C factor and the R factor,and 41.31%was caused by the change in the R factor.There were relatively few areas with increased soil erosion modulus,of which 64.10%of the area where soil erosion increased was caused by the change in the C factor,and 23.88%was caused by the combined effects of the C factor and the R factor.Therefore,the combined effects of the C factor and the R factor were regarded as the main driving force for the decrease of soil erosion,while the C factor was the dominant factor for the increase of soil erosion.The area with decreased soil erosion caused by the C factor(12.10×10^3 km^2)was larger than the area with increased soil erosion caused by the C factor(8.30×10^3 km^2),which indicated that vegetation had a positive effect on soil erosion.This study generally put forward a new method for quantitative assessment of the impacts of the influencing factors on soil erosion,and also provided a scientific basis for the regional control of soil erosion.
基金supported by National Natural Science Foundation of China (Grant No. 41801099)
文摘Accurate measurements of the associated vegetation phenological dynamics are crucial for understanding the relationship between climate change and terrestrial ecosystems. However, at present, most vegetation phenological calculations are based on a single algorithm or method. Because of the spatial, temporal, and ecological complexity of the vegetation growth processes, a single algorithm or method for monitoring all these processes has been indicated to be elusive. Therefore, in this study, from the perspective of plant growth characteristics, we established a method to remotely determine the start of the growth season(SOG) and the end of the growth season(EOG), in which the maximum relative change rate of the normalized difference vegetation index(NDVI) corresponds to the SOG, and the next minimum absolute change rate of the NDVI corresponds to the EOG. Taking the Three-River Headwaters Region in 2000–2013 as an example, we ascertained the spatiotemporal and vertical characteristics of its vegetation phenological changes. Then, in contrast to the actual air temperature data, observed data and other related studies, we found that the SOG and EOG calculated by the proposed method is closer to the time corresponding to the air temperature, and the trends of the SOG and EOG calculated by the proposed method are in good agreement with other relevant studies. Meantime, the error of the SOG between the calculated and observed in this study is smaller than that in other studies.
基金This research is jointly funded by Key Technologies Research and De-velopment Program of China(Grant No.2017YFC0404503)funding project for basic scientific research operations of China’s Central Public Welfare Scientific Research Institutes(AR2117).
文摘The Three-River Headwater Region(TRHR)of China is a typical representative of the alpine environment in the Central Asian plateau and the alpine grassland in the world.Grassland degradation is one of its serious eco-logical problems.The purpose of this study is to quantify the joint impacts of climate and human activities on grassland changes in TRHR after two phases of Ecological Conservation and Construction Project(Ecological Project).Grassland vegetation coverage is selected as an indicator for analyzing grassland changes.We adopt Sen+Mann-Kendall trend analysis,residual trend analysis and correlation analysis methods to analyze the trends in spatial-temporal changes and driving factors of grassland in TRHR from 2000 to 2019.The results show that:(1)The grassland has been mainly restored,and the degraded grassland area only accounts for 1.66%of TRHR.After the implementation of the first phase of the Ecological Project,the percentage of restored grassland area has significantly increased from 8.82%to 24.57%,and slightly decreased during the second phase.(2)The establish-ment of national nature reserves and the implementation of the Ecological Project have changed the situation that“the grassland inside the reserve is worse than that outside the reserve”.(3)Grassland restoration is mainly af-fected by the joint effects of climate and human activities.Nevertheless,grassland degradation is mainly affected by human activities such as overgrazing and grassland reclamation.All of these findings can enrich our under-standing of grassland restoration in TRHR.Artificial measures have certain limitations in promoting grassland restoration.Natural restoration should be considered when human beings strengthen ecological conservation and transform their production and life styles.
文摘The ecological environment of the Three-River Headwater Region is primitive and unique,and sensitive and complex to external influences.The Three-River Headwater Region is the largest nature reserve in China,and is also a nature reserve with the highest concentration of biodiversity in the world's high-altitude areas,so the protection of ecological diversity in this region is particularly important.Ecological diversity is the material basis on which the entire humanity depends to survive and develop.It not only provides humans with basic needs such as food,energy and materials,and is also extremely important for maintaining ecological balance,regulating the climate and promoting the sustainable development of the region.Studying the topographical heterogeneity of the region is first of all a true grasp of the topography of the region,which has certain guiding significance for people's production and life.In addition,studying the impact of topographical heterogeneity on the climate of the region will help to study the formation and variation of regional climate.
基金supported by the Foundation of Director of Institute of Remote Sensing and Digital Earth,Chinese Academy of Sciences(Y4SY0200CX)the Special Project on High Resolution of Earth Observation System for Major Function Oriented Zones Planning(00-Y30B14-9001-14/16)
文摘The three-river source region (TRSR, including Yangtze, Yellow and Lancang rivers), located in the Qinghai-Tibetan Plateau, China, is a typical alpine zone with apparent ecosystem vulnerability and sensitivity. In this paper, we introduced many interdisciplinary factors, such as landscape pattern indices (Shannon diversity index and Shannon evenness index) and extreme climate factors (number of extreme high temperature days, number of extreme low temperature days, and number of extreme precipitation days), to establish a new model for evaluating the spatial patterns of ecosystem vulnerability changes in the TRSR. The change intensity (CI) of ecosystem vulnerability was also analyzed. The results showed that the established evaluation model was effective and the ecosystem vulnerability in the whole study area was intensive. During the study period of 2001–2011, there was a slight degradation in the eco-environmental quality. The Yellow River source region had the best eco-environmental quality, while the Yangtze River source region had the worst one. In addition, the zones dominated by deserts were the most severely deteriorated areas and the eco-environmental quality of the zones occupied by evergreen coniferous forests showed a better change. Furthermore, the larger the change rates of the climate factors (accumulative temperature of ≥10°C and annual average precipitation) are, the more intensive the CI of ecosystem vulnerability is. This study would provide a scientific basis for the eco-environmental protection and restoration in the TRSR.
基金Under the auspices of the Second Tibetan Plateau Scientific Expedition and Research(STEP)Program(No.2019QZKK0106)the Key Technologies Research on Development and Service of Yellow River Simulator for Super-Computing Platform(No.201400210900)the‘Beautiful China’Ecological Civilization Construction Science and Technology Project(No.XDA23100203)。
文摘As the source of the Yellow River,Yangtze River,and Lancang River,the Three-River Source Region(TRSR)in China is very important to China’s ecological security.In recent decades,TRSR’s ecosystem has degraded because of climate change and human disturbances.Therefore,a range of ecological projects were initiated by Chinese government around 2000 to curb further degradation.Current research shows that the vegetation of the TRSR has been initially restored over the past two decades,but the respective contribution of ecological projects and climate change in vegetation restoration has not been clarified.Here,we used the Moderate Resolution Imaging Spectroradiometer(MODIS)Enhanced Vegetation Index(EVI)to assess the spatial-temporal variations in vegetation and explore the impact of climate and human actions on vegetation in TRSR during 2001–2018.The results showed that about 26.02%of the TRSR had a significant increase in EVI over the 18 yr,with an increasing rate of 0.010/10 yr(P<0.05),and EVI significantly decreased in only 3.23%of the TRSR.Residual trend analysis indicated vegetation restoration was jointly promoted by climate and human actions,and the promotion of human actions was greater compared with that of climate,with relative contributions of 59.07%and40.93%,respectively.However,the degradation of vegetation was mainly caused by human actions,with a relative contribution of71.19%.Partial correlation analysis showed that vegetation was greatly affected by temperature(r=0.62,P<0.05)due to the relatively sufficient moisture but lower temperature in TRSR.Furthermore,the establishment of nature reserves and the implementation of the Ecological Protection and Restoration Program(EPRP)improved vegetation,and the first stage EPRP had a better effect on vegetation restoration than the second stage.Our findings identify the driving factors of vegetation change and lay the foundation for subsequent effective management.
文摘蒸散发(Evapotranspiration,ET)是陆地水、碳和能量交换的重要组成部分。基于不同模型和不同遥感数据估算的ET,存在不同程度的不确定性。贝叶斯模型平均(Bayesian model averaging,BMA)提供了降低不确定性的一种途径。本研究采用中国三江源地区水热通量观测数据,以ARTS、PT-JPL、MOD16和SSEBop遥感蒸散发产品为基础,进行了BMA集成研究,生成了三江源地区2003–2015年250 m空间分辨率的年均地表蒸散发数据集。通过验证各输入模型和BMA集成模型结果,发现基于BMA的ET与通量观测数据相关性达0.94,能够解释观测数据季节变化的89%,优于单个模型的性能。说明BMA模型集成能够整合不同模型内在优势,降低结果估算的不确定性,从而获得更可靠的估算结果。本数据集可为三江源区域水热变化研究和生态系统调节功能评估提供更精确的数据支持。
基金supported by Science and Technology Project of China Huaneng Research on Integrated Meteorology and Hydrology Forecasting System in Lancang River Basin(HNKJ21-HF241)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(2019QZKK0207-02)+1 种基金the Research Programme of the Kunming Engineering Corporation Limited(DJ-HXGG-2021-04)the Key Research and Development Programme of Yunnan(202203AA080010)as part of the Science and Technology Plan Project of Yunnan Provincial Department of Science and Technology.Support from Swedish STINT(CH 2019-8377 and CH 2020-8767)is also acknowledged.
文摘The Three-River Headwaters(TRH)region in the Tibetan Plateau is vulnerable to climate change;changes in summer(June–August)precipitation have a significant impact on water security and sustainability in both local and downstream areas.However,the changes in summer precipitation of different intensities over the TRH region,along with their influencing factors,remain unclear.In this study,we used observational and ERA5 reanalysis data and employed a precipitation categorization and water vapor budget analysis to quantify the categorized precipitation variations and investigate their possible linkages with the water vapor budget.Our results showed an increasing trend in summer precipitation at a rate of 0.9 per year(p<0.1)during 1979–2020,with a significant dry-to-wet transition in 2002.The category‘very heavy precipitation’(10 mm d−1)contributed 65.1%of the increased summer precipitation,which occurred frequently in the northern TRH region.The dry-to-wet transition was caused by the effects of varied atmospheric circulations in each subregion.Southwesterly water vapor transport through the southern boundary was responsible for the increased net water vapor flux in the western TRH region(158.2%),while southeasterly water vapor transport through the eastern boundary was responsible for the increased net water vapor flux in the central TRH(155.2%)and eastern TRH(229.2%)regions.Therefore,we inferred that the dry-to-wet transition of summer precipitation and the increased‘very heavy precipitation’over the TRH was caused by increased easterly and southerly water vapor transport.
基金The Chinese National Non-profit Program for Environment Protection,No.201109030
文摘The Three-River Headwaters region in China is an ecological barrier providing en- vironmental protection and regional sustainable development for the mid-stream and down- stream areas, which also plays an important role in animal husbandry in China. This study estimated the grassland yield in the Three-River Headwaters region based on MODIS NPP data, and calculated the proper livestock-carrying capacity of the grassland. We analyzed the overgrazing number and its spatial distribution characteristics through data comparison be- tween actual and proper livestock-carrying capacity. The results showed the following: (1) total grassland yield (hay) in the Three-River Headwaters region was 10.96 million tons in 2010 with an average grassland yield of 465.70 kg/hm2 (the spatial distribution presents a decreasing trend from the east and southeast to the west and northwest in turn); (2) the proper livestock-carrying capacity in the Three-River Headwaters region is 12.19 million sheep units (hereafter described as "SU"), and the average stocking capacity is 51.27 SU [the proper carrying capacity is above 100 SU/km2 in the eastern counties, 60 SU/km2 in the cen- tral counties (except Madoi County), and 30 SU/km2 in the western counties]; and (3) total overgrazing number was 6.52 million SU in the Three-River Headwaters region in 2010, with an average overgrazing ratio of 67.88% and an average overgrazing number of 27.43 SU/km2 A higher overgrazing ratio occurred in Tongde, Xinghai, Yushu, Henan and Z^kog. There was no overgrazing in Zhiduo, Tanggula Township and Darlag, Qumerleb and Madoi. The re- mainder of the counties had varying degrees of overgrazing.
基金National Key Technology R&D Programme of China, No.2009CB421403
文摘Based on the precipitation and temperature data of the 12 meteorological stations in the "Three-River Headwaters" region and the observed runoff data of Zhimenda in the headwater sub-region of the Yangtze River, Tangnaihai in the headwater sub-region of the Yellow River and Changdu in the headwater sub-region of the Lancang River during the period 1965-2004, this paper analyses the trends of precipitation, temperature, runoff depth and carries out significance tests by means of Mann-KendalI-Sneyers sequential trend test. Mak- kink model is applied to calculate the potential evaporation. The runoff model driven by pre- cipitation and potential evaporation is developed and the influence on runoff by climate change is simulated under different scenarios. Results show that during the period 1965-2004 the temperature of the "Three-River Headwaters" region is increasing, the runoff of the three hydrological stations is decreasing and both of them had abrupt changes in 1994, while no significant trend changes happen to the precipitation. The runoff model suggests that the precipitation has a positive effect on the runoff depth, while the potential evaporation plays a negative role. The influence of the potential evaporation on the runoff depth of the Lancang River is found to be the significant in the three rivers; and that of the Yellow River is the least. The result of the scenarios analysis indicates that although the precipitation and the potential evaporation have positive and negative effects on runoff relatively, fluctuated characteristics of individual effect on the runoff depth in specific situations are represented.
基金National Key Research and Development Program of China,No.2016YFC0500205National Basic Research Program of China(973 Program),No.2015CB954103,No.2015CB954101
文摘The Three-River Headwater Region(TRHR), known as the "Water Tower of China", is an important ecological shelter for national security interests and regional sustainable development activities for many downstream regions in China and a number of Southeast Asian countries. The TRHR is a high-elevation, cold environment with a unique, but typical alpine vegetation system. Net primary productivity(NPP) is a key vegetation parameter and ecological indicator that can reflect both natural environmental changes and carbon budget levels. Given the unique geographical environment and strategic location of the TRHR, many scholars have estimated NPP of the TRHR by using different methods; however, these estimates vary greatly for a number of reasons. To date, there is no paper that has reviewed and assessed NPP estimation studies conducted in the TRHR. Therefore, in this paper, we(1) summarized the related methods and results of NPP estimation in the TRHR in a systematic review of previous research;(2) discussed the suitability of existing methods for estimating NPP in the TRHR and highlighted the most significant challenges; and(3) assessed the estimated NPP results. Finally, developmental directions of NPP estimation in the TRHR were prospected.
基金The National Science and Technology Support Plan, No.2009BAC61B01
文摘Based on a monthly dataset of precipitation time series (1961-2010) from 12 me- teorological stations across the Three-River Headwater Region (THRHR) of Qinghai Province China, the spatio-temporal variation and abrupt change analysis of precipitation were exam- ined by using moving average, linear regression, spline interpolation, the Mann-Kendall test and so on. Major conclusions were as follows. (1) The long-term annual and seasonal pre- cipitation in the study area indicated an increasing trend with some oscillations during 1961-2010; however, the summer precipitation in the Lantsang (Lancang) River Headwater Region (LARHR), and the autumn precipitation in the Yangtze River Headwater Region (YERHR) of the THRHR decreased in the same period. (2) The amount of annual precipita- tion in the THRHR and its three sub-headwater regions was greater in the 1980s and 2000s. The springs were fairly wet after the 1970s, while the summers were relatively wet in the 1960s, 1980s and 2000s. In addition, the amount of precipitation in the autumn was greater in the 1970s and 1980s, but it was relatively less for the winter precipitation, except in the 1990s (3) The normal values of spring, summer, winter and annual precipitation in the THRHR and its three sub-headwater regions all increased, but the normal value of summer precipitation in the LARHR had a negative trend and the normal value of winter precipitation declined in general. (4) The spring and winter precipitation increased in most of the THRHR. The summer autumn and annual precipitation increased mainly in the marginal area of the west and north and decreased in the regions of Yushu, Zaduo, Jiuzhi and Banma. (5) The spring and winter precipitation in the THRHR and its three sub-headwater regions showed an abrupt change, except for the spring precipitation in the YARHR. The abrupt changes of spring precipitation were mainly in the late 1980s and early 1990s, while the abrupt changes of winter precipita- tion were primary in the mid- to late 1970s. This research would be helpful for further under- standing the trends and periodicity of precipitation and for watershed-based water resource management in the THRHR.