Three-River Source Region Research Articles

Controlling soil total nitrogen factors across shrublands in the Three Rivers Source Region of the Tibetan Plateau

Alpine shrublands in the Three Rivers Source Region (TRSR) store substantial soil total nitrogen (N); however, limited information is available regarding its storage and controlling factors. To quantify the storage and controlling factors of soil total N stock, we analysed 66 soil profiles from samples obtained from 22 shrubland sites located across the TRSR on the Tibetan Plateau. Analytical methods, such as ordinary least squares regression, one-way analysis of variance, curve estimation, and variation partitioning were used to evaluate the effects of soil characteristics (soil organic carbon), vegetation characteristics (community types and ground cover of shrublands), climatic factors (mean annual temperature - MAT), and topographical features (slope) on soil N stock. Our results showed that soil N storage at a soil depth interval of 0-100 cm was 63.10 ± 27.41 Tg (Tg = 1012 g), with an average soil N stock of 2.44 ± 1.06 kg m-2 in the TRSR shrublands. Although the type of vegetation community had a small effect on soil N stock, the latter increased with increasing shrubland ground cover and soil organic carbon. However, soil N stock decreased with increasing topographical slope and MAT. Furthermore, changes in MAT primarily affected the N stock of topsoil. Among all the controlling factors, soil organic carbon explained most of the variation in the soil N stock. Considering the effects of global warming, an increase in MAT has decreased the soil N stock. Long-term monitoring of changes in soil N stock should be conducted to improve the precise estimation of soil N storage across the shrublands in the TRSR of the Tibetan Plateau.

Interannual variations of monthly precipitation and associated mechanisms over the Three River Source region in China in winter months

AbstractThis study investigates the interannual variability of winter precipitation over the Three River Source (TRS) region in China based on precipitation observations collected at stations in the TRS region and reanalysis datasets for the period of 1980–2015. The results suggest that the TRS winter precipitation has distinct interannual variability with discordant trends in different months, that is, an increasing trend is found in November and February, a decreasing trend is found in other winter months, and interannual variations in precipitation are different in different months. The mechanisms for the interannual variation in monthly precipitation over the TRS region are significantly different in different winter months. The interannual variability of TRS precipitation in November is modulated by an anomalous westerly water vapour transport (WVT) branch. This anomalous WVT branch is related to a North Atlantic‐Europe‐Tibetan Plateau (NA‐E‐TP) wave‐train that originates in the North Atlantic due to the ocean–atmosphere interaction. In December, a circum‐global teleconnection (CGT) wave‐train can induce anomalous westerly WVT in the TRS region, resulting in increased precipitation there. This CGT wave‐train is triggered by warm SST anomalies in the central‐eastern tropical Pacific associated with the El Niño‐Southern Oscillation (ENSO). The interannual variability of TRS precipitation in January and February is affected by southwesterly WVT anomalies over the TRS region, which are associated with a southeastward propagating wave‐train over Eurasia caused by the North Atlantic Oscillation (NAO). In March, the interannual variability of TRS precipitation is modulated by the leading mode of the Eurasian circulation that resembles the Scandinavian (EU1) pattern, which can cause anomalous southwesterly WVT in the TRS region. In winter, the characteristics of sea surface temperature anomalies, weather systems, and atmospheric circulations associated with interannual variations of monthly precipitation in the TRS region are different for individual winter months.

Remote sensing inversion of grassland aboveground biomass based on high accuracy surface modeling

Accurate and effective accounting of grassland aboveground biomass (AGB) is essential for grassland carbon storage accounting and pastoral agriculture sustainability. In this study, we combined AGB field survey data and remote sensing data to build a suitable model to estimate the grassland AGB in the Three-River Source Region (TRSR) of China. Three machine learning models were used to simulate the grassland AGB from 2001 to 2019, including support vector machine (SVM), random forest (RF), and high accuracy surface modeling (HASM). The results show that (1) the HASM achieved better results than the RF and SVM models (R2 = 0.8459 > 0.72 > 0.5858; RMSE = 29 < 41 < 56), and the HASM results reproduce the spatial distribution characteristics of the biomass well. The subsequent spatiotemporal analysis of the AGB conducted in this study was based on the results of the HASM. (2) The highest AGB was located in the eastern and central-southern parts of the TRSR, and the lowest AGB was distributed in the western region. (3) The overall change in the AGB revealed that the percentage of the area that experienced a significant increase in AGB (21%) was larger than that of the area that experienced a significant decrease (13%), and the stable areas accounted for 66% of the total area. The grassland AGB increased by 1 g/m2/yr during 2001–2019. (4) The factors driving the changes in the AGB were analyzed. Overall, the warm and wet climate conditions promoted grass growth in most regions of the TRSR. (5) However, the biomass decreased in some regions with warm and wet conditions. For example, overgrazing and increased populations of grazing led to significant biomass decreases in the towns of Ziketang and Heka in Xinghai County. In this study, the grassland AGB was simulated based on the HASM model, with a high accuracy and a spatial resolution of 500 m. The results of this study provide a scientific basis for grassland resource protection and the highly effective implementation of grassland restoration projects in China.

Parameter Sensitivities of the Community Land Model at Two Alpine Sites in the Three-River Source Region

The three-river source region plays an important role on China’s ecological security and Asia’s water supply. Historically, the region has experienced severe ecological degradation due to climate change and human activities. Reasonable simulations of the energy and water cycles are essential to predict the responses of land surface processes to future climate change. Current land surface models involve empirical functions that are associated with many parameters. These parameter uncertainties will largely affect the simulation when applied to a new domain. The Community Land Model (CLM) is a widely used land surface model, and version 5.0 is the newest version. Compared to the prior version CLM4.5, CLM5.0 has largely updated plant hydraulic and stomatal conductance schemes. How these changes affect parameter sensitivities is unknown. In our work, we tested 17 key parameters in CLM4.5 and 19 parameters in CLM5.0 at two eddy flux sites in the three-river source region: the Maqu and Maduo sites. We adopted the simplest one-at-a-time changes on each parameter and quantified their sensitivities by the parameter effect (PE). We found that the Maqu site was more sensitive to vegetation parameters, while the Maduo site was more sensitive to the initial soil water content in both CLM4.5 and CLM5.0. This is because Maduo grid cell has wetland that does not respond to vegetation parameters in CLM, which may not reflect the reality. Further model development on wetland vegetation parameterization is important. Our validation on the default simulation showed CLM5.0 did not always improve the simulations. The largest difference between CLM5.0 and CLM4.5 was that soil moisture (SM) showed a much stronger decrease in response to a higher leaf area index (LAI) in CLM5.0 than in CLM4.5, suggesting that SM is more sensitive to vegetation changes in CLM5.0.

Variations of Vegetation Phenology Extracted from Remote Sensing Data over the Tibetan Plateau Hinterland during 2000–2014

How vegetation phenology responds to climate change is a key to the understanding of the mechanisms driving historic and future changes in regional terrestrial ecosystem productivity. Based on the 250-m and 8-day moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) data for 2000–2014 in the Three-River Source Region (TRSR) of Qinghai Province, China, i.e., the hinterland of the Tibetan Plateau, we extracted relevant vegetation phenological information (e.g., start, end, and length of growing season) and analyzed the changes in the TRSR vegetation in response to climate change. The results reveal that, under the increasingly warm and humid climate, the start of vegetation growing season (SOS) advanced 1.03 day yr−1 while the end of vegetation growing season (EOS) exhibited no significant changes, which led to extended growing season length. It is found that the SOS was greatly affected by the preceding winter precipitation, with progressively enhanced precipitation facilitating an earlier SOS. Moreover, as the variations of SOS and its trend depended strongly on topography, we estimated the elevation break-points for SOS. The lower the elevations were, the earlier the SOS started. In the areas below 3095-m elevation, the SOS delay changed rapidly with increasing elevation; whereas above that, the SOS changes were relatively minor. The SOS trend had three elevation break-points at 2660, 3880, and 5240 m.

Improved evaluation method of the soil wind erosion intensity based on the cloud–AHP model under the stress of global climate change

Under the stress of global climate change, soil wind erosion has become a major environmental issue in the Three-River Source Region (TRSR) of China. However, few large-scale studies have been conducted on soil wind erosion owing to the lack of investigational data or complex parameters. Moreover, the uncertainty and randomness in the weight determination process cannot be avoided using the traditional method. Thus, a cloud–analytic hierarchy process (cloud–AHP) model was proposed to construct a wind erosion intensity index model for the TRSR based on seven typical land surface parameters. The following results were obtained. (1) The cloud–AHP model can better eliminate the randomness and uncertainty in the weight determination process. (2) The proposed evaluation method of wind erosion intensity has better applicability in the TRSR with overall accuracy of 93%. (3) The overall wind erosion intensity in this region is moderate. The wind erosion intensity was the largest in the Yangtze River (0.55, moderate erosion) and smallest in the source region of the Lancang River (0.50, mild erosion). (4) Significant differences are observed in the influences of various vegetation types on wind erosion intensity. Bare land exhibits the highest wind erosion intensity, whereas a coniferous forest exhibits the smallest. Moreover, grassland is a key control zone of soil and water conservation because it has the largest spatial heterogeneity of internal erosion intensity. These results can provide data and technical support for preventing and controlling soil erosion and protecting the environment in the region.

Overload type and optimization of meadow carrying capacity in Maqin County in the Three-River Source Region, China

Alpine meadows, comprising the main ecosystem of the Three-River Source Region, play an important role in the economic development of western pastoral areas. To determine whether the grazing level was too intense or the nutrient-carrying capacity of the meadows was overloaded, and to offer solutions in Maqin County, Qinghai Province, China, the meadows carrying capacity was determined by combining grass-yield and nutrients data for different seasons across different meadows. The results showed that the levels of crude protein (CP), ether extract (EE), ash, soluble sugars (SS), gas production, and energy value of forage in the summer–autumn grazing meadows were higher than those of the winter–spring meadows. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) of forage in the summer–autumn grazing meadows were lower than those of the winter–spring meadows. We found that no pastures were overloaded with metabolizable energy (ME) for the whole year but digestible crude protein (DCP) was overloaded in winter–spring. And there were differences in the amount carrying capacity (forage yield) of seasonal grazing meadows for the different herds, the overload types were annual overloading (herd A), overloaded in summer–autumn (herd B), overloaded in winter–spring (herd C), and not overloaded (herd D). Compared with the previous grazing mode, theoretical carrying capacity, DCP carrying capacity, and ME carrying capacity of herd A increased by 20, 19, and 27 sheep units, respectively, after optimization; herd B: 36, 31, and 45 sheep units, respectively; herd C: 28, 23, and 44 sheep units, respectively; and herd D: 43, 40, and 61 sheep units, respectively. In the Three-River Source Region and similar alpine pastoral areas, the grassland-livestock structure should be optimized to improve grassland vegetation status and increase the theoretical carrying capacity.

Dynamic Changes of Plateau Wetlands in the Damqu River Basin, Yangtze River Source Region, China, 1988–2015

The assessment of wetland changes on the Tibetan Plateau (TP) is an important component of global change research. The Damqu River Basin (DRB) lies within the southern source of the Yangtze River and is part of the core wetlands area of the Three Rivers Source Region (TRSR). We examined the distribution of wetlands across this region based on remote sensing image interpretations. The results revealed clear evidence of changes over the period between 1988 and 2015, with the ​​wetland area in 2015 being 8964.51 km2 (53.52% of the total basin). Wetlands at this time were concentrated between 4700 and 5000 m (upper limit: 5600 m), with land slopes between 0 and 6°, and a northward aspect. The data also showed that the wetland area decreased by 71.16 km2 between 1988 and 2015, equivalent to 0.79% of the 1988 total. The annual value of the normalized difference vegetation index (NDVI) decreased over 63.36% of the region within the DRB during 1988–2015. The area of three major lakes in the DRB declined from 2009 to 2015. The results of this analysis demonstrated that precipitation variation was the underlying cause of the observed vegetation index and lake area changes within the DRB between 1988 and 2015.

Identification of conflict between wildlife living spaces and human activity spaces and adjustments in/around protected areas under climate change：A case study in the Three-River Source Region

Overlap between wildlife living spaces and human activity spaces represents one of the main causes of human-wildlife conflict. It is therefore necessary to identify and adjust the spatial distribution of conflicts because climate change will modify the ranges and locations of species. The MaxEnt model was used to simulate the distribution of wildlife living spaces under current and future climatic conditions (RCP4.5 scenario) based on species distribution data and environmental data from the Three-River Source Region. Furthermore, the logistic-cellular automata model was used to simulate the changes in human activity spaces (construction land and arable land) by 2050. Areas of overlap between wildlife living spaces and human activity spaces were determined by overlay analysis. Then, the areas of construction and arable land that would conflict with wildlife were redistributed outside highly suitable wildlife living spaces. In addition, ecological corridors connecting current and future living spaces were planned for the migration of certain species in response to climate change based on the minimum cumulative resistance model. The results showed that the areas of highly suitable wildlife living spaces will decrease under the influence of climate change if global warming occurs. In the future, the area of overlap between highly suitable wildlife living spaces and construction land will be 125 km2, and that between highly suitable wildlife living spaces and arable land will be 340 km2. The redistribution of these areas will cause human activity spaces to become more concentrated. Moreover, 110 ecological corridors should be constructed across roads in the Three-River Source Region.

A new remote-sensing-based indicator for integrating quantity and quality attributes to assess the dynamics of ecosystem assets

Ecological benefits provided by ecosystem assets play an important role in improving human wellbeing. However, there are few feasible methods to combine data on the quantity and quality of ecosystem assets to describe their state and trend. Here, we developed a new remote-sensing-based indicator by synthesizing ecosystem asset quantity and quality data for effective assessment at a regional or national scale. The new indicator includes a typological ecosystem asset index (TEAI) (e.g., forest ecosystem asset index) and an integrated ecosystem asset index (IEAI). The TEAI and IEAI can be used to assess the state and trend of a specific ecosystem or set of regional ecosystems, respectively. We applied the new indicator in the context of ecological protection policy in the Three-Rivers Source Region (TRSR), a region known as the ‘Chinese water tower’. From 2000 to 2015, the IEAI increased by 4.02% due to an increase in the ecosystem asset area (0.2%) and the ecosystem asset quality (0.66% and 0.02% increases in excellent and good level ecosystem assets, respectively). The implementation of ecological protection and ecological restoration programs was the main direct driver of regional ecological asset improvement. Our results suggest the new indicator is feasible for quickly and accurately evaluating the state and trend of ecosystem assets and can be used to guide ecosystem management at a large regional scale.

A preliminary assessment of environmental flow in the three rivers' source region, Qinghai Tibetan Plateau, China and suggestions

The three rivers' source region (TRSR) located in the Qinghai-Tibetan Plateau is an important ecological region of China for its location and high elevation. However, the ecological condition of the region is critical to water conservation and ecological security in China. Therefore, the present study focused on determining the environmental flow requirements (EFRs) of the Lancang (above Xiangda streamflow gauge), Yangtze (Zhimenda), and Yellow (Tangnaihai) Rivers, which will be helpful in the sustainable development of the region. Because of lacking ecological data, we used four hydrological methods (i.e., flow duration curve shifting, Tennant, flow duration curve analysis, and low flow index method) to assess the EFRs for the minimum and optimum eco-environmental conditions of these rivers. Since there was missing data on most gauges and we had streamflow data of only one gauge (Zhimenda) in the Yangtze headwater region, a hydrological model was applied to complete the missing data and simulate the streamflow data for the Tuotuo, DamChu, Chumar, and Tongtian Rivers for the estimation of the EFRs insides the region. The environmental flows of 118 m3/s (76% of mean annual flow, MAF), 312 m3/s (72% of MAF), 484 m3/s (77% of MAF) were determined for the conservation of the optimum riverine ecosystem and 67 m3/s (43% of MAF), 155 m3/s (36% of MAF), and 290 m3/s (47% of MAF) for the minimum eco-environmental conditions for the Lancang, Yangtze, Yellow Rivers, respectively. It was also noticed that low flow months (November to April) required more proportions of mean monthly flow than high flow months (May to October). These preliminary results will be very supportive of the water resources managers and policymakers in the case of any sustainable socio-economic development in the region.

Spatial and temporal change patterns of net primary productivity and its response to climate change in the Qinghai-Tibet Plateau of China from 2000 to 2015

The vegetation ecosystem of the Qinghai-Tibet Plateau in China, considered to be the “natural laboratory” of climate change in the world, has undergone profound changes under the stress of global change. Herein, we analyzed and discussed the spatial-temporal change patterns and the driving mechanisms of net primary productivity (NPP) in the Qinghai-Tibet Plateau from 2000 to 2015 based on the gravity center and correlation coefficient models. Subsequently, we quantitatively distinguished the relative effects of climate change (such as precipitation, temperature and evapotranspiration) and human activities (such as grazing and ecological construction) on the NPP changes using scenario analysis and Miami model based on the MOD17A3 and meteorological data. The average annual NPP in the Qinghai-Tibet Plateau showed a decreasing trend from the southeast to the northwest during 2000–2015. With respect to the inter-annual changes, the average annual NPP exhibited a fluctuating upward trend from 2000 to 2015, with a steep increase observed in 2005 and a high fluctuation observed from 2005 to 2015. In the Qinghai-Tibet Plateau, the regions with the increase in NPP (change rate higher than 10%) were mainly concentrated in the Three-River Source Region, the northern Hengduan Mountains, the middle and lower reaches of the Yarlung Zangbo River, and the eastern parts of the North Tibet Plateau, whereas the regions with the decrease in NPP (change rate lower than −10%) were mainly concentrated in the upper reaches of the Yarlung Zangbo River and the Ali Plateau. The gravity center of NPP in the Qinghai-Tibet Plateau has moved southwestward during 2000–2015, indicating that the increment and growth rate of NPP in the southwestern part is greater than those of NPP in the northeastern part. Further, a significant correlation was observed between NPP and climate factors in the Qinghai-Tibet Plateau. The regions exhibiting a significant correlation between NPP and precipitation were mainly located in the central and eastern Qinghai-Tibet Plateau, and the regions exhibiting a significant correlation between NPP and temperature were mainly located in the southern and eastern Qinghai-Tibet Plateau. Furthermore, the relative effects of climate change and human activities on the NPP changes in the Qinghai-Tibet Plateau exhibited significant spatial differences in three types of zones, i.e., the climate change-dominant zone, the human activity-dominant zone, and the climate change and human activity interaction zone. These research results can provide theoretical and methodological supports to reveal the driving mechanisms of the regional ecosystems to the global change in the Qinghai-Tibet Plateau.

Changes in the depths of seasonal freezing and thawing and their effects on vegetation in the Three-River Headwater Region of the Tibetan Plateau

Frozen ground degradation plays an important role in vegetation growth and activity in high-altitude cold regions. This study estimated the spatiotemporal variations in the active layer thickness (ALT) of the permafrost region and the soil freeze depth (SFD) in the seasonally frozen ground region across the Three Rivers Source Region (TRSR) from 1980 to 2014 using the Stefan equation, and differentiated the effects of these variations on alpine vegetation in these two regions. The results showed that the average ALT from 1980 to 2014 increased by 23.01 cm/10a, while the average SFD decreased by 3.41 cm/10a, and both changed intensively in the transitional zone between the seasonally frozen ground and permafrost. From 1982–2014, the increase in the normalized difference vegetation index (NDVI) and the advancement of the start of the vegetation growing season (SOS) in the seasonally frozen ground region (0.0078/10a, 1.83d/10a) were greater than those in the permafrost region (0.0057/10a, 0.39d/10a). The results of the correlation analysis indicated that increases in the ALT and decreases in the SFD in the TRSR could lead to increases in the NDVI and advancement of the SOS. Surface soil moisture played a critical role in vegetation growth in association with the increasing ALT and decreasing SFD. The NDVI for all vegetation types in the TRSR except for alpine vegetation showed an increasing trend that was significantly related to the SFD and ALT. During the study period, the general frozen ground conditions were favorable to vegetation growth, while the average contributions of ALT and SFD to the interannual variation in the NDVI were greater than that of precipitation but less than that of temperature.

Responses of soil moisture to regional climate change over the Three Rivers Source Region on the Tibetan Plateau

AbstractIn this study, soil moisture data from two reanalysis datasets (ERA‐Interim, ERA5), a satellite soil moisture product from the European Space Agency (ESA) and three assimilation datasets from the Global Land Data Assimilation System (GLDAS), that is, GLADS‐NOAH025, GLADS‐NOAH10, and GLDAS‐CLM were compared with the observed soil moisture data in Maqu and Maduo stations over the Three Rivers Source Region (TRSR) on the Tibetan Plateau in China. Comparative statistical parameters between the soil moisture observations and the products, including the root mean square error, correlation coefficient (R), and standard deviation ratio were calculated to evaluate the products in different seasons. It was found that most products overestimated the soil moisture values, among which GLADS‐NOAH025 had relatively good consistency with the observations in the surface soil layer (0–10 cm), whereas GLDAS‐CLM agreed well with the observations in the 10–40 cm layer. Both ERA5 and ERA‐interim soil moisture overestimated soil moisture at all levels. The responses of soil moisture to regional climate change over the TRSR were also investigated by using the GLDAS‐NOAH025 soil moisture product, the ESA soil moisture product, and the observations during the nonfreezing period. The results show that the trends of soil moisture are consistent with the precipitation changes in the main central part of the TRSR. A significant positive correlation was found between soil moisture and precipitation in most regions of the TRSR, which indicates that soil moisture increases with the increase of precipitation, except in the northwest TRSR, where the variation of soil moisture was possibly influenced by both the precipitation changes and the increase of evapotranspiration.

Risk prevention and control strategies for the severely affected areas of snow disaster in the Three Rivers Source Region (TRSR), China

Risk prevention and control strategies for the severely affected areas of snow disaster in the Three Rivers Source Region (TRSR), China

Comprehensive Research on Remote Sensing Monitoring of Grassland Degradation: A Case Study in the Three-River Source Region, China

In this study, we proposed climate use efficiency (CUE), a new index in monitoring grassland ecosystem function, to mitigate the disturbance of climate fluctuation. A comprehensive evaluation index (EI), combining with actual vegetation net primary productivity (NPP), CUE, vegetation coverage, and surface bareness, was constructed for the dynamic remote sensing monitoring of grassland degradation/restoration on a regional scale. By using this index, the grassland degradation/restoration in the Three-River Source Region (TRSR) was quantitatively evaluated during 2001–2016, which has been an important ecological barrier area in China. Results showed the following: During the study period, the grassland of Yellow River source (SRYe) had high vegetation coverage, NPP, CUE, and low bareness, whereas Yangtze River source (SRYa) had low vegetation coverage, NPP, CUE, and high bareness. The vegetation coverage and CUE of the grassland showed upward trends, with annual change rates of 0.75% and 0.45% year −1. The surface bareness and NPP showed downward trends, with annual change rates of −0.37% year−1 and −0.24 g C m−2 yr−2, respectively. Assessment of EI revealed that 67.18% of the grassland of TRSR showed a recovery trend during the study period. The overall restoration of the SRYe was the best, followed by SRYa. However, the status of Lancang River source (SRLa) was poor.

Comparison of energy partitioning between artificial pasture and degraded meadow in three-river source region on the Qinghai-Tibetan Plateau: A case study

To reveal the differences in energy exchange between a degraded alpine meadow (DM) and an artificial pasture (AP, that was artificially planted with Elymus nutans on the ploughed degraded meadow), the energy partitioning and its biophysical controls were compared between the two study sites in the Three-River Source Region (TRSR) on the Qinghai-Tibetan Plateau. The mean maximum leaf area index (LAI) for AP and DM was 2.66 and 1.08 m2 m−2, respectively. The net radiation (Rn), sensible heat flux (H), latent heat flux (λE), and soil heat flux (G) showed similar seasonal changes for the two study sites; no obvious differences in energy partitioning were noted between AP and DM during the non-growing season. However, during the growing season, Rn of DM was about 5.4% higher than that of AP, although almost the same downward shortwave and longwave radiation was received at both sites. Moreover, the mean albedo (α) of DM was lower by 0.02 than that of AP, and the mean soil surface temperature of DM was 4.1 °C lower than that of AP. The partitioning of available energy into H and λE of DM differed markedly from those of AP, and the λE/Rn ratio of DM was 16.4% higher than that of AP, whereas the H/Rn ratio of the former was 20.9% lower than that of the latter during the growing season. The growing season (annual) mean Bowen ratio (β) was 0.69 ± 0.04 and 0.90 ± 0.03 (2.38 ± 0.09 and 2.93 ± 0.12) at DM and AP, respectively, indicating that more available energy of DM was used for λE in comparison with that for AP. The difference in vegetation was considered to be the major factor leading to differences in the energy partitioning between the two sites. The results of the case study suggest that meadow degradation increases water loss through evapotranspiration and that enlarging the area of artificial pasture can increase the plant productivity and improve the water conservation capacity in this region.

Storage, patterns and controls of soil organic carbon in the alpine shrubland in the Three Rivers Source Region on the Qinghai-Tibetan Plateau

Alpine shrubland ecosystems in the Three Rivers Source Region (TRSR) store substantial soil organic carbon (SOC), but the storage, patterns and control of SOC in those ecosystems have rarely been investigated. In this study, using data from 66 soil profiles surveyed from 22 sites between 2011 and 2013, we estimated the storage and patterns of SOC, and their relationships with climatic factors, elevation, ground cover and slope. Our results showed that SOC storage in the top 100 cm across the TRSR shrubland was 0.68 ± 0.38 Pg C, with an average SOC density (soil carbon storage per area) of 26.21 ± 14.58 kg m−2. Spatially, SOC density increased with longitude and latitude. Vertically, SOC in the topsoil at 30 cm and 50 cm accounted for 56% and 75%, respectively, of the total at 100 cm. SOC density showed a decreasing trend with increasing elevation, but it was greater in regions of higher ground cover. The density had no relationship with either mean annual precipitation or slope. Increasing mean annual temperature had positive effects on SOC density, which is inconsistent with the global trend. With increasing soil depth, however, the effects of temperature on SOC density were not significant. Therefore, in a global warming scenario, increasing temperature gives shrubland considerable C sink potential on the topsoil, and the regions of C sequestration differ as a result of uneven increases in temperature. Hence, further monitoring of dynamic changes is necessary to provide a more accurate assessment of potential C sequestration in TRSR shrubland.

Interannual Variation of the Spring and Summer Precipitation over the Three River Source Region in China and the Associated Regimes

AbstractThis study analyzes the interannual and interdecadal variability of spring and summer precipitation over the Three River Source (TRS) region in China using four datasets. A general consistency is revealed among the four datasets with regard to the interannual and interdecadal variability of TRS precipitation during 1979–2015, demonstrating a confidence of the four datasets in representing the precipitation variability over the TRS region. The TRS spring and summer precipitation shows distinct interannual and interdecadal variability, with an overall increasing trend in the spring precipitation and an interdecadal oscillation in the summer precipitation. The regimes associated with the interannual variability of TRS spring and summer precipitation are further investigated. The interannual variability of TRS spring precipitation is essentially modulated by an anomalous easterly water vapor transport (WVT) branch associated with the leading mode of Eurasian spring circulation. El Niño–Southern Oscillation (ENSO) may affect the interannual variability of TRS spring precipitation by causing southerly WVT anomalies toward the TRS region. The interannual variability of TRS summer precipitation is essentially modulated by an anomalous southwesterly WVT branch over the TRS region, which is mainly associated with a Eurasian wave train connected with the summer North Atlantic Oscillation. A strong East Asian summer monsoon and an El Niño–decaying summer may also contribute to the southwesterly WVT anomalies over the TRS region.

Enhanced connections between summer precipitation over the Three-River-Source region of China and the global climate system

This study reveals an enhanced correlation between the interannual variability of summer precipitation over the Three-River-Source (TRS) region of China and North Atlantic Oscillation (NAO), western Indian Ocean sea surface temperature (SST), El Nino-Southern Oscillation (ENSO), and the East Asian summer monsoon (EASM) for past decades, revealing an enhanced connection between the summer climate of the TRS region and the global climate system. Underlying causes are investigated based on a comparison on the climate effects associated with the aforementioned factors between periods 1961–1980 and 1991–2014. Enhanced connections to NAO are mainly attributed to the fact that the increased atmospheric moisture over the Arctic region has an enhanced latent heating on convective activity over the Hudson Bay-Davis Strait region under negative-phase NAO, generating an intensified anomalous high over Greenland and further stimulating an Eurasian wave-train influencing the TRS region. Similarly, for an El-Nino decaying summer, convection anomalies over the Maritime Continent are more significant due to enhanced latent heating observed in 1991–2014, which in turn have a more significant influence on the summer climate in TRS region. Regarding western Indian Ocean SSTs, warming in the western Indian Ocean is characterized by a warming center north (south) of the equator for 1991–2014 (1961–1980); correspondingly, the associated Kelvin wave-induced Ekman divergence mechanism is more pronounced over the Bay of Bengal and South China Sea for 1991–2014. Enhanced connections to the EASM are mainly attributable to a combined effect of Indian Ocean warming and anomalous convective activity over the Maritime Continent associated with ENSO.