Headwater Region Research Articles

Projected Intensified Hydrological Processes in the Three‐River Headwater Region, Qinghai Tibetan Plateau

AbstractThe Three‐River Headwater Region, also known as China's water tower, is highly sensitive to climate change and has experienced profound hydrological alterations in the last few decades. This study assessed the potential impacts of climate change on all the important hydrological components such as precipitation, evapotranspiration, streamflow, snow‐melt flow, and soil moisture (SM) content in the region. For this, climate data (i.e., temperature, precipitation, relative humidity, and windspeed) of three Global Climate Models (i.e., CanESM5, MPI‐ESM1.2‐HR, and NorESM2‐MM) was downscaled with the Statistical DownScaling Model (SDSM) and their ensemble was forced into a hydrological model to simulate the hydrological processes for 1981–2100. The screening process, which is central to all downscaling techniques, is very subjective in the SDSM. Therefore, we developed a quantitative screening approach by modifying the method applied by Mahmood and Babel (2013, https://doi.org/10.1007/s00704‐012‐0765‐0) for the selection of a set of logical predictors to cope with multi‐collinearity and their ranking. The analyses were performed for the near future period (NFP, 2021–2060) and far future period (FFP, 2061–2100) relative to the baseline period (BLP, 1981–2020). The results showed that the region will be hotter and wetter in the future, with intensive and frequent floods. For example, temperature, precipitation, evapotranspiration, and streamflow will increase by 1.0–1.5 (1–1.9)°C, 9–21 (15–27)%, 6–17 (9–29)%, and 9–46 (22–64)% in the NFP and by 2.0–2.8 (2.7–4.6)°C, 16–40 (43–87)%, 11–31 (24–73)%, and 20–95 (60–198)% in the FFP, respectively, under SSP2‐4.5 (SSP5‐8.5). Similar projections were explored for other hydrological components. Among all, surface flow showed an unprecedented increase (500%–1,000%) in the FFP. Peak flows will be much higher and will shift forward, and snowmelt will start earlier in the future. The results of the present study can be a good source for understanding the hydrological cycle and be used for the planning and management of water resources of the highly elevated and complex region of the Qinghai Tibetan Plateau.

Effects of hillslope aspect on erosion rate of alpine meadows in the Three-River Headwater Region, China

Soil erosion causes serious grassland degradation in the Three-River Headwater Region (TRHR) of the Qinghai-Tibet Plateau. Identifying source areas of erosion is important, including understanding the influences of hillslope aspect on soil erosion. However, the effect of hillslope aspect on soil erosion is a much-debated process, wherein contrasting results were previously reported. We hypothesized that aspect-induced differences in environmental variables will be related to differences in erosion magnitude and spatial pattern, and that these differences will impact soil physiochemical characteristics as well. To test this hypothesis, soil samples were collected at conjoined south- and north-facing hillslopes along elevational profiles in a small watershed in Yushu County, with measurements of soil water content (SWC), soil organic carbon (SOC), soil organic matter (SOM), soil particle size distribution, soil total nitrogen (STN) and phosphorus (STP). Soil erosion rate was estimated using 137Cs technology. The results showed that soil erosion rates of the two hillslopes ranged from 0.073 to 10.83 t ha-1 yr-1, and were 3 times greater on the south-facing hillslope. Soil water content ranged from 7.6% to 76.8% on the two hillslopes with lower values on the south-facing hillslope due to the greater solar radiation. By Spearman correlation analysis and path analysis, we concluded that lower soil water content on the south-facing hillslope restricts vegetation growth, and hence resulting in greater soil erosion under the case where vegetation growth is dominantly controlled by water availability. Greater soil erosion on the south-facing hillslope caused greater surficial accumulation of coarser materials and greater loss of soil nutrients, which are expected to complicate the hydrological erosion process. Moreover, the downslope increased soil erosion rate should be fully considered in conservation practices. These results will improve our understanding of the interaction and feedback mechanisms between soil characteristics, vegetation function, and soil erosion in the TRHR.

Less concentrated precipitation and more extreme events over the Three River Headwaters region of the Tibetan Plateau in a warming climate

Widely known as the “China Water Tower”, changes in precipitation concentration and insufficient rainfall days over the Three River Headwaters region (TRH) may threaten food and water security in TRH and downstream areas. However, current research on rainfall occurrences in TRH lacks a comprehensive understanding of the spatiotemporal variations in precipitation concentration, the seasonal distribution of rainy days across different rainfall categories, and their correlations with global warming. In this study, we utilize the CN05.1 gridded daily rainfall dataset to address these gaps. Our analysis reveals a decreasing trend in both the precipitation concentration index (PCI) and precipitation concentration degree (PCD), accompanied by an earlier onset of the precipitation concentration period (PCP) in TRH over the past six decades. The distribution of monthly rainfall becomes more uniform throughout the year, with precipitation spreading across a greater number of days annually. Notably, the reduction in both the number of rainy days and the proportion of rainfall during the summer, along with the decrease in the frequency of light and moderate rainfall days and the increase in the frequency of moderately heavy and heavier rainfall days, will lead to a more extreme distribution of summer precipitation in TRH. The increase in the number of rainy days across all intensity categories and the proportion of precipitation during winter, has favorable implications for the sustainable development and water security in TRH. Additionally, the relative increase in the occurrence of heavy and extremely heavy rainfall days in spring demonstrates the most pronounced change, with a notable rise of 12.74% to 28.24% per decade. This provides a certain degree of alleviation for spring drought in TRH. Furthermore, we find that for every 1-degree Celsius increase in global temperature, both PCI and PCD decrease by 9.82% and 8.5%, and PCP advances by 6.41 days. With the 50th percentile of precipitation serving as a dividing line, stronger precipitation events beyond this threshold exhibit a higher positive response to global warming. Conversely, weaker precipitation events falling below the 50th percentile show a higher negative response to global warming. Light rainy days decrease by 16.2% per degree Celsius of warming, while very heavy and extremely heavy rainy days increase by 26.4% and 27.5%, respectively. These findings have important implications for mitigating droughts and floods, as well as for developing a comprehensive framework for the management of water resources and agricultural irrigation in TRH.

Bacterial rarity in a subarctic stream network: Biodiversity patterns, assembly mechanisms and types of rarity.

Dendritic stream networks are an intriguing subject for exploring the spatial and temporal variability of the rare and common bacterial biosphere, yet very few such studies have been conducted. We sampled riverine bacterioplankton at 13 sites in a subarctic riverine network across 3 years, with five sampling times each year. Ordinations showed a consistent pattern of downstream shift for both rare and abundant subcommunities. We also detected a temporal signal, with seasonal community shifts reflecting changes in water temperature and groundwater contribution, and an inter-annual pattern where the year 2018 differed from other years. Phylogenetic turnover of the rare subcommunity indicated homogeneous selection, whereas the abundant subcommunity was mainly stochastically structured. Transiently rare taxa were the dominant type of rarity with the highest proportion at the headwater regions. The bacterioplankton community was characterized by a small group of core taxa that occurred at most sites with little temporal variation, a very large number of permanently or transiently rare taxa, and taxa shifting through time between the rare and abundant biosphere. While this basic structure could have been detected with less extensive temporal replication, a comprehensive understanding of the rare biosphere in riverine bacterioplankton can only be achieved via inter-annual, spatially replicated sampling that covers the whole stream network.

Responses of annual streamflow variability to annual precipitation, extreme climate events and large-scale climate phenomena in the Qinghai-Tibet Plateau

Solar activity and large-scale climate phenomena have significant effects on extreme climate events and streamflow variability. As the roof of the world and the water tower of Asia, the Qinghai-Tibet Plateau (QTP) is highly sensitive to climate change. Therefore, it is of great significance to study the relationship between extreme hydrometeorological events of the QTP and climate change for global hydroclimate research. In this study, we analyzed the spatiotemporal variation and significant oscillation period of several hydrometeorological variables such as extreme precipitation indices (EPIs), extreme temperature indices (ETIs) and annual streamflow variability based on the observation data of hydrometeorological stations in the QTP during 1962–2019 using Sen’s slope estimator, Mann-Kendall test and continuous wavelet analysis (CWT). And the teleconnection patterns and the lead-lag relationship between annual precipitation, extreme climate events, multiple nonstationary climate mode and annual streamflow were evaluated using wavelet coherence (WTC). The results show that the climate of the QTP has been wetter and warmer in the past 58 years. The annual streamflow of several natural rivers in the QTP mainly show an increasing trend over the last 60 years. The annual streamflow of natural river (except Yellow River) increases significantly in three-rivers headwater region, and the rivers in the northeast and northwest also show a significant increase trend, but there is no significant change in the natural river streamflow in the south of QTP. In addition, the annual streamflow of natural rivers had significant periodicities in the bands of 2–4 years, 4–7 years and 7–11 years. The significant coherence of WTC spectra between annual precipitation and streamflow indicate that precipitation is the main reason for annual streamflow variation in the QTP. The variation of extreme climate events significantly regulates the regional annual streamflow. All EPIs except consecutive dry days show an in-phase correlation with annual streamflow of most headwater. Annual streamflow of Naijin River is positively and negatively correlated with extreme warm and extreme cold, respectively, and has a clearer lead-lag relationship than that with EPIs. Annual streamflow of headwater has higher correlations with EI Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) than with sunspot number (SSN). Solar activity may first affect ENSO and PDO, and then this effect is transferred sequentially to the hydrological cycle of the QTP by SSN-modulated PDO and PDO-SSN co-modulated ENSO. It is of great significance to investigate the response of streamflow variation to annual precipitation, extreme climate events and large-scale climate phenomena for water resources management, flood control, ecosystem restoration, and the well-being of surrounding residents and sustainable development in the QTP.

Biology, distribution, and conservation of the Gamilaroi crayfish Euastacus gamilaroi Morgan, 1997 (Decapoda: Astacidea: Parastacidae), a freshwater crayfish from New South Wales, Australia

Abstract Euastacus gamilaroi Morgan 1997, the Gamilaroi crayfish, was initially described based on specimens collected in 1954 from Hanging Rock, New South Wales, but since then scant subsequent records hinder conservation of this endangered species. Extensive sampling during 2006–2023 delineated the distribution, habitat preferences, biological traits, and conservation status of the species. Together with concurrent molecular taxonomic analyses were extend the species range from headwater regions of highland streams above 960 m altitude of Burrows Creek to include highland streams of Duncan and Dungowan creeks (Peel-Namoi River/western drainage) and Tomalla, Back, and Ben Halls creeks (Barnard-Manning River/eastern drainage). We provide information on the distribution, biology, and ecological associations of the species. Results advocate for the classification of E. gamilaroi as an endangered species, recognizing its distinctive ecological niche and its status as a climate refugee, aiming to protect this rare species from climate-related challenges. We also present a taxonomic key differentiating E. gamilaroi from other species of Parastacidae in the region.

Soil water sources and their implications for vegetation restoration in the Three-Rivers Headwater Region during different ablation periods

Abstract. Amid global warming, the timely supplementation of soil water is crucial for the effective restoration and protection of the ecosystem. It is therefore of great importance to understand the temporal and spatial variations of soil water sources. The research collected 2451 samples of soil water, precipitation, river water, ground ice, supra-permafrost water, and glacier snow meltwater in June, August, and September 2020. The goal was to quantify the contribution of various water sources to soil water in the Three-Rivers Headwater Region (China) during different ablation periods. The findings revealed that precipitation, ground ice, and snow meltwater constituted approximately 72 %, 20 %, and 8 % of soil water during the early ablation period. The snow is fully liquefied during the latter part of the ablation period, with precipitation contributing approximately 90 % and 94 % of soil water, respectively. These recharges also varied markedly with altitude and vegetation type. The study identified several influencing factors on soil water sources, including temperature, precipitation, vegetation, evapotranspiration, and the freeze–thaw cycle. However, soil water loss will further exacerbate vegetation degradation and pose a significant threat to the ecological security of the “Chinese Water Tower”. It emphasizes the importance of monitoring soil water, addressing vegetation degradation related to soil water loss, and determining reasonable soil and water conservation and vegetation restoration models.

Riverine carbon dioxide release in the headwater region of the Qilian Mountains, northern China

Rivers are important sources of the carbon dioxide (CO2) released into the atmosphere; however, research on CO2 emission from riverine headwater regions is sparse, particularly from rivers in the Tibetan Plateau (TP) region, which has large area of glaciers and permafrost. We conducted a three-year (2020–2022) observational study of CO2 flux rates from the riverine headwater region of the Qilian Mountains (QLMs) to determine diel and seasonal CO2 variations and flux rates. Our results revealed that the annual average CO2 emission was 0.45 (0.03–1.60) kg CO2 m−2 yr−1, with the highest flux rates observed in winter [0.87 (0.08–2.67) μmol CO2 m−2 s−1], which was approximately three times higher than flux rates in other seasons. Glacier meltwater altered the diel pattern of riverine CO2 flux rates by diluting CO2 and dissolved inorganic carbon. Meanwhile, CO2 release from rivers in the permafrost region was dictated by stream order, with a linear decrease as stream order increased. Considering diel variations, the total CO2 fluxes from the headwater regions of the QLMs were approximately 32.70 (25.00–41.28) Gg C/yr, representing 76 % of the pre-calibration total CO2 fluxes ignoring diel variations. This study provides essential insights into CO2 release from headwaters, which have substantial implications for understanding CO2 outgassing.

Recent intensified erosion and massive sediment deposition in Tibetan Plateau rivers

Recent climate change has caused an increase in warming-driven erosion and sediment transport processes on the Tibetan Plateau (TP). Yet a lack of measurements hinders our understanding of basin-scale sediment dynamics and associated spatiotemporal changes. Here, using satellite-based estimates of suspended sediment, we reconstruct the quantitative history and patterns of erosion and sediment transport in major headwater basins from 1986 to 2021. Out of 13 warming-affected headwater regions, 63% of the rivers have experienced significant increases in sediment flux. Despite such intensified erosion, we find that 30% of the total suspended sediment flux has been temporarily deposited within rivers. Our findings reveal a pronounced spatiotemporal heterogeneity within and across basins. The recurrent fluctuations in erosion-deposition patterns within river channels not only result in the underestimation of erosion magnitude but also drive continuous transformations in valley morphology, thereby endangering local ecosystems, landscape stability, and infrastructure project safety.

How much we know about precipitation climatology over Tianshan Mountains––the Central Asian water tower

Tianshan Mountains are the headwater regions for the central Asia rivers, providing water resources for ecological protection and economic development in semiarid regions. Due to scarce observations, the hydroclimatic characteristics of the Tianshan Mountains Precipitation (TMP) measured over highland (>1500 m) regions remain to be revealed. Here, we show the TMP belongs to a monsoon-like climate regime, with a distinct annual range and a high ratio of summer-to-yearly rainfall, and exhibits six abrupt changes, dividing the annual cycle into six precipitation sub-seasons. Over the past 60 years, the yearly TMP has significantly increased by 17.3%, with a dramatic increase in winter (135.7%). The TMP displays a significant 40-day climatological intra-seasonal oscillation (CISO) in summer. The TMP CISO’s wet phase results from the confrontation of the eastward propagating mid-tropospheric Balkhash Lake Low and the southward migrating Mongolian High. The sudden changes in the two climatological circulation systems trigger TMP’s changes, shaping the 40-day CISO. Emerging scientific issues are also discussed.

Comparison and Optimization of Water Conservation Function in Natural Forests and Tea Plantations in a Headwater Catchment, Taihu Lake Basin

The rapid expansion of tea plantations (Camellia sinensis), which replace local natural forests, decreases the water conservation function in the headwater region and threatens regional water security. However, studies focusing on the comprehensive evaluation and improvement of the water conservation function of natural forests and tea plantations are lacking. In this study, we developed a comprehensive evaluation method for the water conservation function by investigating, monitoring, and conducting process model simulations of 221 tea plantation and natural forest (bamboo forest) samples obtained in the field. We also quantified the trade-off between water conservation and carbon sequestration. The results showed that the tea plantations had lower annual water conservation than the bamboo forests. Slope was the most critical influential variable affecting water conservation in tea plantations. Strict control should be exercised in the development of steep slopes above 20° for tea plantations, to enhance the regional water conservation capacity. Water conservation in bamboo forests increased to the maximum level at a planting density (SD) of approximately 2500–2700 tree/ha and then decreased quickly. The optimal SD values of bamboo forests were 2500, 2600, and 2650 trees/ha at slopes of 10°, 15°, and 20°, respectively, which can maintain higher water conservation and adequate carbon sequestration. Overall, water conservation and carbon sequestration increased by approximately 22.6% and 13.7%, respectively, compared with the average values for bamboo forests. However, at slopes >20°, a strong trade-off was observed between water conservation and carbon sequestration, and competing ecosystem services accompanied those, which were hard to balance and which resulted here in disproportionate water conservation at the cost of carbon sequestration loss.

Primary driving factors of ecological environment system change based on directed weighted network illustrating with the Three-River Headwaters Region

The primary driving factors of ecological environment change have received significant attention. However, previous research methods for identifying the main drivers of ecological environment change have primarily relied on correlation analysis and regression analysis. While these methods can reveal co-occurrences, associations, and correlations among elemental characteristics, they often struggle to uncover the deep-seated interactions among elements within complex, unstable, nonlinear, and high-dimensional systems. To address this, we used the Three-River Headwaters Region as a case study and introduced a complex network model from the perspective of the ecological environment system to investigate the main driving factors of ecological environment change. In our analysis, we considered 12 factors related to the atmosphere, hydrology, vegetation, and soil, including evaporation, long-wave radiation, short-wave radiation, specific humidity, soil temperature, precipitation rate, soil water content, air temperature, air pressure, vegetation normalization index, wind speed, and natural surface runoff. Watersheds were selected as the fundamental units for constructing ecological environment datasets. We applied the Ensemble Empirical Mode Decomposition (EEMD) method and Hilbert-Huang Transform (HHT) to analyze causal relationships between time series pairs and constructed two directed weighted network models based on sub-catchments. The results showed that both network models yielded consistent conclusions, with the sparse network exhibiting higher efficiency. Radiation and temperature were identified as the primary driving factors of ecosystem change, and the water cycle was determined to be the ultimate manifestation of ecological system change throughout the Three-River Headwaters Region. Furthermore, based on node out-strength, we generated a vegetation protection priority map.

DNA barcode shows discordant cases among morphological and molecular species identification in Isbrueckerichthys (Siluriformes: Loricariidae)

Abstract Isbrueckerichthys is a genus of armored catfish (Siluriformes: Loricariidae) with five species in the lowlands from the Ribeira de Iguape basin and in the uplands of the Tibagi River basin. Despite the validation of the morphological species, molecular data to investigate gene flow and species delimitation have not been completed for all species. For this purpose, we compared sequences of COI region associated with barcoding molecular identification, aiming for a species delimitation analysis and generating population data of I. alipionis, I. epakmos, I. duseni, I. cf. duseni, I. saxicola, and I. calvus. The K2P genetic distance, molecular species delimitation analysis, and well-sustained branches in the phylogenetic tree validate I. alipionis, I. epakmos, and I. duseni, and suggest I. cf. duseni as a valid molecular operational taxonomic unit. However, no differences were detected between I. saxicola and I. calvus. The discordance between molecular and morphological species may be due to the recent dispersal of some Isbrueckerichthys representatives at the border between the Ribeira de Iguape and Tibagi basins. The isolation features of the mountainous region of Ribeira de Iguape basin and headwaters captures to uplands are presented to explain the dispersion and the cases of incipient speciation in Isbrueckerichthys lineages.

Integrating impacts of climate change on aquatic environments in inter-basin water regulation: Establishing a critical threshold for best management practices

Inter-basin water diversion (IBWD) is a viable strategy to tackle water scarcity and quality degradation due to climate change and increasing water demand in headwaters regions. Nevertheless, the capacity of IBWD to mitigate the impacts of climate change on water quality has rarely been quantified, and the underlying processes are not well understood. Therefore, this study aims to elucidate how the IBWD manipulated total phosphorus (TP) loading dilution and conveying patterns under climate change and determine a critical threshold for the quantity of water entering downstream reservoirs (WIN) for operational scheduling. To resolve this issue, climate-driven hydrologic variability over a 60-year period was derived utilizing the least square fitting approach. Subsequently, six scenarios evaluating the response of in-lake TP concentrations (TPL) to increased temperatures and IBWDs of 50 %, 100 %, and 150 % from the baseline water volume in 2030 and 2050 were studied by employing a calibrated hydrological-water quality model (SWAT-YRWQM). In the next stage, three datasets derived from mathematical statistics based on the observed data, the Vollenweider formula, and modeled projections were integrated to formulate best management practices. The results revealed that elevated air temperatures would lead to reduced annual catchment runoff but increased IBWD. Additionally, our study quantified the IBWD potential for mitigating water quality degradation, indicating the adverse effects of climate change on TPL would be weakened by 4.2–14.4 %. A critical threshold for WIN was also quantified at 617 million m3, maintaining WIN at or near 617 million m3 through optimized operational scheduling of IBWD could effectively restrict external inflow TP loading to lower levels. This study clearly illustrates the intricate interactive effects of climate change and IBWD on aquatic environments. The methodology elucidated in this study for determining the critical threshold of WIN could be applied in water management for analogous watershed-receiving waterbody systems.

Erosional modulation of the balance between alkalinity and acid generation from rock weathering

The balance between alkalinity generation by carbonate and silicate weathering and sulfuric acid generation by sulfide weathering controls the effect of weathering on atmospheric pCO2 over geologic timescales. How this balance varies across environmental gradients remains poorly constrained. Here, we analyze this balance across an erosional gradient of two orders of magnitude in the Three Rivers (Yangtze, Mekong, and Salween Rivers) Headwater Region (TRHR), eastern Qinghai-Tibet Plateau (QTP). By employing major element chemistry and multiple isotopes (δ34SSO4, δ18OSO4, and δ18OH2O) coupled with forward and inverse approaches, we unmix contributions of silicates, carbonates, evaporites, and sulfides to the total weathering budget. Across the TRHR, riverine SO42– is derived mainly from a mixture of an evaporite source with uniform values of δ34SSO4 and δ18OSO4, and a sulfide source that contributes highly variable values of δ34S (−12.2 ‰ to +4.1 ‰) and δ18O (−17.7 ‰ to −1.6 ‰). Contributions of sulfide oxidation to riverine SO42– vary from 16 % to 94 %, and sulfuric acid consumes 6 % to 63 % of the alkalinity produced by weathering. The fractions of weathering alkalinity derived from carbonate weathering range from 36 % to 98 % relative to silicate weathering. The combination of silicate, carbonate, and sulfide weathering suggests that the instantaneous weathering fluxes of most sampled catchments in the TRHR act as a sink of atmospheric CO2 over timescales shorter than marine carbonate burial (∼104 years), but as a carbon source over timescales longer than carbonate burial and shorter than sulfide burial (∼107 years). The spatial variability of the balance between alkalinity and acid generation, and, thus, the relationship between chemical weathering and atmospheric pCO2, are largely dependent on lithology. However, within comparable lithologic settings, sulfide and carbonate weathering rates rise with increasing erosion, whereas silicate weathering rates remain constant. Consequently, plateau weathering shifts from a sink to a source of atmospheric CO2 with increasing erosion. These findings suggest that sulfide weathering is more sensitive to erosion than carbonate and silicate weathering, and that it could play an important role in the long-term carbon cycle during mountain building.

A spatio-temporal fusion strategy for improving the estimation accuracy of the aboveground biomass in grassland based on GF-1 and MODIS

The accurate estimation of the aboveground biomass (AGB) is crucial for the sustainable utilization and management of grassland resources. Spatio-temporal inconsistencies between field samples and satellite images are major source of error in the estimation of grassland AGB. To solve this problem, this study selected the Three Rivers Headwater Region as the study area and proposed a selection strategy for base-period images of spatio-temporal fusion that was suitable for use at a large spatial scale in which cloud-free images are difficult to obtain. The spatial and temporal adaptive reflectance fusion model (STARFM) based on the selection strategy was used to generate a synthetic Normalized Difference Vegetation Index (NDVI) dataset with high spatial-temporal resolution by using the maximum value composite of GF-1 NDVI and MODIS NDVI to enhance the spatial-temporal quality of the images for field-scale application. Three estimation models for grassland AGB were then constructed by the random forest algorithm using synthetic NDVI, MODIS NDVI, GF-1 NDVI respectively, together with ancillary data. Following this, the estimation model with the highest accuracy was used to generate a 16-m eight-day time-series AGB in the growing season. The results showed: (1) The synthetic NDVI was correlated closely with the observed GF-1 NDVI, with an average R of 0.825 and a RMSE of 0.087. The temporal trend of the synthetic NDVI for each grassland type was highly consistent with that of the MODIS NDVI in the growing season with a correlation higher than 0.9. (2) The synthetic NDVI reduced the spatial difference between field samples and images to 16-fold, and the temporal difference was controlled to within four days under ideal conditions. (3) The synthetic NDVI improved the estimation accuracy of grassland AGB by about 15.9% and 19.7% (R2), and 13.7% and 17.5% (RMSE) relative to MODIS NDVI and GF-1 NDVI, respectively. (4) The time-series AGB revealed accurately the spatial distribution of and seasonal temporal variations in the grassland biomass. The results of this study may serve as scientific guidance for timely monitoring of grassland conditions and precise management of grassland resources in China.

Enhancing sustainable livelihoods in the Three Rivers Headwater Region: A geospatial and obstacles context

Applying novel approaches to assess the sustainable livelihood potentially contribute to learning and managing social-ecological systems. This research demonstrates the trajectory of sustainable livelihoods in the Three Rivers Headwater Region (TRHR) of Western China for a period of 2003 to 2017, utilizing a bespoke Sustainable Livelihood Index (SLI). Devised through a top-down data collation method, the SLI integrates comprehensive official statistics, encompassing socio-economic metrics alongside climatic and other environmental conditions. We employed spatial visualization and cold hotspot analysis to discern the spatio-temporal nuances of the SLI. Furthermore, the Obstacle Factor Analysis (OFA) was implemented to identify salient barriers impacting the SLI. Results indicated a steady rise in the SLI over the examined period, indicating progressive enhancements in the livelihood sustainability. However, marked disparities were observed across the TRHR counties, reflecting heterogeneity in socioeconomic progress and resource allocation. While Yushu county displayed commendable growth, Jiuzhi county stood out as a significant cold spot. Notably, natural and financial resources surfaced as paramount stresses to SLI progression, emphasizing the necessity for robust resource management and economic support. Key challenges, such as the grassland carrying pressure index, deteriorated grassland territories, and per capita disposable income were identified as critical obstacles to the sustainable livelihood of pastoral communities. These factors collectively influence economic viability, grassland resource stewardship, and human capital development, which are intertwined with local economic gains and future potentials. In nutshell, this study highlights the multifaceted challenges faced by the TRHR in charting sustainable livelihood pathways and champions recalibrated policies to protect natural assets, amplify economic support, reinforce human capital, and nurture regional synergies for sustainable evolution. The key insights suggest the pressing need for innovative, nature-based solutions that amplify regional-scale livelihood resilience, especially considering the challenges related to natural assets, financial support, and human capital development.

Trends and contribution of different grassland types in restoring the Three River Headwater Region, China, 1988–2012

Rapid greening of the Qinghai–Tibet Plateau had been confirmed, but the contributions to the overall change and its causes in various grassland types has been less studied. Previous research has focused on exogenous factors such as climate change and human activities, rather than on endogenous factors, such as grassland types. Using net primary productivity (NPP), precipitation and temperature data, we applied trend, contribution and pull contribution analysis to understand the spatiotemporal evolution and driving factors of six different grassland types at a pixel scale in the Three River Headwater Region (TRHR) of China from 1988 to 2012. The results showed that grassland NPP in the TRHR increased at an average growth amount of 3.46 gC m−2 yr−1 and an average growth rate of 2.26 %. The average growth amount of alpine desert and alpine steppe (0.42 gC m−2 yr−1, 1.74 gC m−2 yr−1, respectively) showed great potential improvement. The average growth rate (1.27 %, 1.87 %) of montane meadow and alpine meadow, respectively, presented a high potential to increase (P < 0.05). Alpine meadow, montane meadow and temperate steppe were positive pullers to the average growth amount. Alpine steppe and alpine desert were positive pullers to the average growth rate. In general, alpine meadow had the highest growth amount contribution (84.86 %), while alpine meadow and alpine steppe had the highest contribution to the growth rate (62.16 %, 34.24 %, respectively). The study implied that, in addition to external factors, differences in internal factors such as the community composition and structure of different grassland types could also affected the grassland recovery process. These results contribute to understanding the specific differences in the contribution of regional grassland restoration processes from vegetation composition. Assessing grasslands with the potential to increase productivity, we can provide scientific reference for implementing more precise and efficient measures in future grassland management restoration.

Variation of hydro-climatic extremes in headwater regions of Hei River basin under climate change

Study regionHeadwater regions of Hei River basin, located in the northeast of Tibetan Plateau. Study focusHydro-climatic extremes analysis for historical (1971–2015) and future (2024–2100) period. New hydrological insights for the regionRemarkable climate change has been observed in high mountain areas, which may result in more frequent hydro-climatic extremes. Investigating hydro-climatic extremes variations is important for mitigating hydro-climatic disasters and implementing water resource management. Warm extremes present an increasing trend in frequency and magnitude for historical and future period, while the cold extremes show a decreasing trend in the study area. Meanwhile, frequency and amount of precipitation extremes present an increasing trend for historical and future period. As a result, the intensity of meteorological and hydrological droughts show decreasing trends while floods present an increasing trend, indicating a certain drought relief in the study area. But future occurrence of extreme droughts or floods will increase. Moreover, floods for different return periods will rise with different change rate under different scenarios (SSP 1–2.6, SSP 2–4.5, SSP 3–7.0 and SSP 5–8.5). Therefore, extreme floods or droughts risks should not be underestimated and need be addressed accordingly. The findings highlight the importance of adaptive strategies to cope with more frequent hydro-climatic extremes under climate change.

Modeling the impact of climate change on streamflow in glacier/snow-fed northern Tianshan basin

Study regionUrumqi River headwater region in eastern Tianshan, central Asia. Study focusClimate change is anticipated to accelerate glacier shrinkage and alter hydrological conditions, causing variations in the runoff patterns in the catchment and significantly threatening the regional water resources. However, few models exhibit adequate performance to simulate both surface alterations and glacier/snow runoff. Therefore, this study combined the glacier module with the Soil and Water Assessment Tool (SWAT) model to estimate the effect of climate change on the streamflow in the Urumqi River headwater region. The Urumqi River Headwater region is representative because of its long data series, viatal location, and local water availability, and it contains the longest-observed reference glacier (Urumqi Glacier No.1) in China, which spans the period from 1958 to the present. New hydrological insights for the regionThe SWAT model performed satisfactorily for both calibration (1983–2005) and validation (2006–2016) periods with a Nash-Sutcliffe efficiency (NSE) greater than 0.80. The water balance analysis suggested that the snow/glacier melt contributed approximately 25% to the water yield. At the end of the 21st century, the temperature would increase by 2.4–3.8 °C while the precipitation would decrease by 1–2% under two future scenarios (ssp245 and ssp585). Thus, a 34–36% reduction in streamflow was projected due to above climate change impacts. This information would contribute to the development of adaptation strategies for sustainable water resource management.