Importance and vulnerability of the world’s water towers

Factors controlling the water quality of rock glacier springs in European and American mountain ranges

Rock glaciers (RGs) provide significant water resources in mountain areas under climate change. Recent research has highlighted high concentrations of solutes including trace elements in RG-fed waters, with negative implications on water quality. Yet, sparse studies from a few locations hinder conclusions about the main drivers of solute export from RGs. Here, in an unprecedented effort, we collected published and unpublished data on rock glacier hydrochemistry around the globe. We considered 201 RG springs from mountain ranges across Europe, North and South America, using a combination of machine learning, multivariate and univariate analyses, and geochemical modeling. We found that 35 % of springs issuing from intact RGs (containing internal ice) have water quality below drinking water standards, compared to 5 % of springs connected to relict RGs (without internal ice). The interaction of ice and bedrock lithology is responsible for solute concentrations in RG springs. Indeed, we found higher concentrations of sulfate and trace elements in springs sourcing from intact RGs compared to water originating from relict RGs, mostly in specific lithological settings. Enhanced sulfide oxidation in intact RGs is responsible for the elevated trace element concentrations. Challenges for water management may arise in mountain catchments rich in intact RGs, and where the predisposing geology would make these areas geochemical RG hotspots. Our work represents a first comprehensive attempt to identify the main drivers of solute concentrations in RG waters.

Evaluating MODIS cloud-free snow cover datasets using massive spatial benchmark data in the Tibetan Plateau

Accurate snow cover data is crucial for understanding climate change, managing water resources, and calibrating models. The MODIS (Moderate-resolution Imaging Spectroradiometer) and its cloud-free snow cover datasets are widely used, but they have not been systematically evaluated due to different benchmark data and evaluation parameters. Conventional methods using station observations as a ground truth suffer from underrepresentation and mismatches in temporal and spatial scales. This study established a scale-matched spatial benchmark dataset, compiling from 18,433 Landsat series and 11,172 Sentinel-2 images over two decades, totaling ∼1.86 billion samples and ∼320 million snow samples. We evaluated seven MODIS cloud-free snow cover datasets for seasons, elevation zones, land covers and subregions using this benchmark data. For the clear-sky part, NIEER_MODIS_SCE (MODIS snow cover extent product over China) performs best due to its use of optimal NDSI thresholds suitable for each land use type. This highlights the importance of regional customization in snow mapping algorithms, and it can be further improved in spring, forests and zone 1 by combining it with M*D10A1GL06. For the cloud removed part, one-step integrated spatiotemporal cloud removal datasets perform better than any other approach does. The second-best dataset is obtained from a simple but effective single temporal cloud removal method using nearby time information. For the whole dataset, the best NIEER_MODIS_SCE has an overall accuracy of 0.82 and snow retrieval accuracy of 84.56 %. It performs excellently in most settings but weakest in forests thus requiring more efficient strategies. This research provides new perspectives and methods for objectively assessing MODIS snow cover products and other relevant datasets. These methods can be readily extended to other regions and adapted to future satellite missions. And such findings may guide the selection of more valid snow cover data and the developing of even better snow detecting strategies.

Nonlinear woody vegetation effects on Holocene fire activity across the world's highlands

The accelerated warming in the world's highlands has prompted significant ecological adjustments and an increase in the frequency of forest fires. Nevertheless, the correlation between woody biomass and increased fire activity in the past has received limited attention. A total of 138 charcoal and 145 pollen records were analyzed to investigate the relationship between fire and woody biomass (arboreal pollen, AP) in the world's highlands during the Holocene. The findings indicate biomass burning in the Rockies, Alps and Andes stepped increased in the early to middle Holocene but decreased in the late Holocene. The positive AP-fuel feedback was recorded in the early-middle Holocene, whereas the negative AP-fuel feedback emerged in the late Holocene, the latter were attributed to denser forests in the Rockies and intensified human activities in the Alps and Andes. Conversely, Holocene biomass burning in the Tianshan-Altai Mountains, Africa and Tibetan Plateaus exhibited overall decreasing trends with sudden decreases in the Tianshan-Altai Mountains and Tibetan Plateau and a notable increase in the African Plateau over the past millennium. The variability observed in fire regime changes in the past millennium is likely influenced by human activities. Results illustrate that fire responses to woody vegetation are nonlinear, such that the same direction of change in vegetation can elicit different fire responses depending on their components at a site. Our study offers crucial insights into the influence of woody biomass on fire dynamics in the world's highlands, providing important contextual information about how these montane systems may respond to future climate change and anthropogenic activity.

The diversity and risk of potential pathogenic bacteria on the surface of glaciers in the southeastern Tibetan Plateau

Glaciers, which constitute the world's largest global freshwater reservoir, are also natural microbial repositories. The frequent pandemic in recent years underscored the potential biosafety risks associated with the release of microorganisms from the accelerated melting of glaciers due to global warming. However, the characteristics of pathogenic microorganisms in glaciers are not well understood. The glacier surface is the primary area where glacier melting occurs that is often the main subject of research on the dynamics of pathogenic microbial communities in efforts to assess glacier biosafety risks and devise preventive measures. In this study, high-throughput sequencing and quantitative polymerase chain reaction methods were employed in analyses of the composition and quantities of potential pathogenic bacteria on the surfaces of glaciers in the southeastern Tibetan Plateau. The study identified 441 potential pathogenic species ranging from 215 to 4.39 × 1011 copies/g, with notable seasonal and environmental variations being found in the composition and quantity of potential pathogens. The highest level of diversity was observed in April and snow, while the highest quantities were observed in October and cryoconite. Host analysis revealed that >70 % of the species were pathogens affecting animals, with the highest proportion of zoonotic pathogens being observed in April. Analysis of aerosols and glacial meltwater dispersion suggested that these microbes originated from West Asia, primarily affecting the central and southern regions of China. Null model analysis indicated that the assembly of potential pathogenic microbial communities on glacier surfaces was largely governed by deterministic processes. In conclusion, potential pathogenic bacteria on glacier surfaces mainly originated from the snow and exhibited significant temporal and spatial variation patterns. These findings can be used to enhance researchers' ability to predict potential biosafety risks associated with pathogenic bacteria in glaciers and to prevent their negative impact on populations and ecological systems.

Snow cover phenology dataset over global mountain regions from 2000 to 2023

Monitoring temporal and spatial changes in the mountain seasonal snowpack is a key step to better quantify the impact of recent climate warming on this very sensitive environment. In this context, to support the research on large scale, there is an urgent need of consistent and accurate data sets over global mountain regions. This paper presents a dataset derived from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery collection 6.1 onboard of Terra satellite containing information on snow cover area and snow cover phenology (duration, start and end of the season) at 500 m ground resolution and covering the global mountain regions as delineated by the Global Mountain Biodiversity Assessment (GMBA) shapefile. The dataset contains yearly averaged snow cover area (SCA), snow cover duration (SCD), first snow day (FSD) and last snow day (LSD). The snow cover area SCA is based on snow cover fraction daily maps averaged on a yearly basis. To derive the snow phenology variables, SCD, FSD, LSD, a second-order autoregressive approach was adopted to interpolate the data thus reducing the impact of cloud coverage. The dataset was processed for the entire MODIS time series starting from October 2000 up to September 2023 and it is provided on yearly basis considering the hydrological year timeframe: from 1st October to 30th September of the subsequent year for the Northern Hemisphere and from 1st April to 31st March of the subsequent year for the Southern Hemisphere. The use of the data can be manyfold from quantifying the snowpack changes in the last 23 years, to addressing the impact of snowpack changes on water resources and vegetation phenology.

Driving factors of the distribution of microplastics in the surface soil of the typical uninhabited and habited areas in the Qinghai-Tibet Plateau, China

Microplastics (MPs) are widely detected in the soil of the Qinghai-Tibet Plateau with increasing economic activities. However, studies concerning the driving factors affecting the presence of these surface soil MPs for the typical regions with different geographic conditions are still lacking. Here we chose three representative regions (Ali, Yushu, and Haixi) from east to west across the plateau to investigate the distribution and further explore the contributing factors of surface soil MPs. The Spearman rank correlation, Geodetector, Random Forest Regression and Principal Component Analysis were used to unveil how the driving factors influence MPs distribution across the plateau. The results revealed that the MPs abundance, type, size, color and polymer across the Ali, Yushu, and Haixi were different. Microplastic abundance was inversely correlated with the distance from roads and residential areas, but was positively related to precipitation. Moreover, traffic elements were the primary source of MPs pollution in the Ali and Yushu but residential activities were the leading source of MPs contamination in the Haixi. Besides, backward trajectory simulations suggested that atmospheric transport may also contribute to the presence of soil MPs in the representative regions. These results further indicated that different regions may require different measures for controlling MPs pollutions in surface soil. This study provides new insights into the distribution and source of MPs and further offers valuable methodology for future research aimed at uncover driving factors contributing MPs pollution across different regions with various geographical conditions.

Historical reconstruction of glacier mass balance and its contribution to water resources in the Sawir Mountains from 2000 to 2020

Glacial changes are crucial to regional water resources and ecosystems in the Sawir Mountains. However, glacial changes, including the mass balance and glacial meltwater of the Sawir Mountains, have sparsely been reported. Three model calibration strategies were constructed including a regression model based on albedo and in-situ mass balance of Muz Taw Glacier (A-Ms), regression model based on albedo and geodetic mass balance of valley, cirque, and hanging glaciers (A-Mr), and degree-day model (DDM) to obtain a reliable glacier mass balance in the Sawir Mountains and provide the latest understanding in the contribution of glacial meltwater runoff to regional water resources. The results indicated that the glacial albedo reduction was significant from 2000 to 2020 for the entire Sawir Mountains, with a rate of 0.015 (10a)-1, and the spatial pattern was higher in the east compared to the west. Second, the three strategies all indicated that the glacier mass balance has been continuously negative during the past 20 periods, and the average annual glacier mass balance was -1.01 m w.e. Third, the average annual glacial meltwater runoff in the Sawir Mountains from 2000 to 2020 was 22 × 106 m3, and its contribution to streamflow was 25.81 % from 2000 to 2018. The glacier contribution rates in the Ulkun- Ulastu, Lhaster, and Kendall River basins were 31.37 %, 22.51 %, and 19.27 %, respectively.

Legacy and alternative perfluoroalkyl acids in the Yellow River on the Qinghai-Tibet Plateau: Levels, spatiotemporal characteristics, and multimedia transport processes

The source region of the Yellow River (SRYR) located in the northeast of the Qinghai-Tibetan Plateau is not only the largest runoff-producing area in the Yellow River Basin, but also the most important freshwater-supply ecological function area in China. In this study, the short-term spatiotemporal distribution of selected legacy and alternative perfluoroalkyl acids (PFAAs) in the SRYR was first investigated in multiple environmental media. Total PFAA concentrations were in the range of 1.16-14.3 ng/L, 4.25-42.1 pg/L, and 0.21-13.0 pg/g dw in rainwater, surface water, and sediment, respectively. C4-C7 PFAAs were predominant in various environmental matrices. Spatiotemporal characteristics were observed in the concentrations and composition profiles. Particularly, the spatial distribution of rainwater and the temporal distribution of surface water exhibited highly significant differences (p<0.01). Indian monsoon, westerly air masses, and local mountain-valley breeze were the driving factors that contributed to the change of rainwater. Rainwater, meltwater runoff, and precursor degradation were important sources of PFAA pollution in surface water. Organic carbon content was a major factor influencing PFAA distribution in sediment. These results provide a theoretical basis for revealing the regional transport and fate of PFAAs, and are also important prerequisites for effectively protecting the freshwater resource and aquatic environment of the Qinghai-Tibetan Plateau.

Quantifying future water resource vulnerability in a high-mountain third pole river basin under climate change

Understanding the water resource vulnerability (WRV) in global mountain regions under climate change is crucial for water resources management and socio-economic development. However, the WRV in the high-mountain Third Pole region (with quite a few transboundary river basins) remains largely unclear. Here, we have applied a comprehensive assessment framework of WRV to a Third Pole high-mountain river basin (Nujiang-Salween River, NSR) and its dependent downstream. The framework consisted of sensitivity, exposure, adaptability, hazard, and water stress indices, considering climate change, socio-economics, government effectiveness, natural disasters, and water supply capacity of the target river basin. Our results indicate that the downstream area (with intensive human activities) often exhibited significantly higher WRV than the mountain region; while the WRV shows an M-shaped change with increasing elevation, with the highest vulnerability occurring in a relatively low elevation range (e.g., 500-1500 m for the NSR basin). In the near future, we find that the spatial pattern of WRV in the basin is alternately influenced by adaptation, water scarcity, and exposure; whereas climate change serves as the main driver affecting the WRV in the far future. These findings enhance our understanding of the WRV in high-mountain transboundary basins of the Third Pole under global change.

Sources and pathways of spring flow and climate change effects in the Dungju Ri & Yude Ri catchments, Bhutan Himalaya

Springs and streams are vital water sources for supporting the livelihood of Himalayan residents. Escalating climate change, population growth, and economic development strain the region's freshwater resources. A national survey reveals declining spring and stream flows in Bhutan, necessitating an improved understanding of their generation. Monthly grab water samples were collected during April 2022-January 2023 from main streams, springs and other source waters at various elevations at Yude Ri and Dungju Ri catchments, Bhutan Himalayas. Samples were analyzed for pH, specific conductance, and major ions and end-member mixing analysis in combination with diagnostic tools of mixing models was used to determine sources, relative contributions, and recharge dynamics of spring flows. The results indicated that direct precipitation dominated spring flows (0.59 ± 0.21), followed by shallow groundwater (0.31 ± 0.18), and soil subsurface water (0.10 ± 0.15). The contributions of spring flow components followed an elevation gradient, with higher and lower fractions, respectively, of direct precipitation and shallow groundwater at higher elevations, e.g., 0.90 ± 0.1 to 0.13 ± 0.08 for direct precipitation and 0.03 ± 0.03 to 0.37 ± 0.19 for shallow groundwater from 3266 m to 1558 m. Spring flows primarily relied on precipitation (∼70 % from both direct precipitation and soil water), making them very sensitive to changes in precipitation. Significant contributions of shallow groundwater also indicated the vulnerability of spring flows to decreased snowfall relative to rainfall and the earlier onset of snowmelt, particularly for those located in the snow-rain transition zone (∼2500 m). Our results suggest high vulnerability of spring flows to the climate change in the Himalayas.

Dark brown carbon from wildfires: a potent snow radiative forcing agent?

Deposition of wildfire smoke on snow contributes to its darkening and accelerated snowmelt. Recent field studies have identified dark brown carbon (d-BrC) to contribute 50-75% of shortwave absorption in wildfire smoke. d-BrC is a distinct class of water-insoluble, light-absorbing organic carbon that co-exists in abundance with black carbon (BC) in snow across the world. However, the importance of d-BrC as a snow warming agent relative to BC remains unexplored. We address this gap using aerosol-snow radiative transfer calculations on datasets from laboratory and field measurement. We show d-BrC increases the annual mean snow radiative forcing between 0.6 and 17.9 W m- 2, corresponding to different wildfire smoke deposition scenarios. This is a 1.6 to 2.1-fold enhancement when compared with BC-only deposition on snow. This study suggests d-BrC is an important contributor to snowmelt in midlatitude glaciers, where ~40% of the world's glacier surface area resides.

Phylotranscriptomic and ecological analyses reveal the evolution and morphological adaptation of Abies

Coniferous forests are under severe threat of the rapid anthropogenic climate warming. Abies (firs), the fourth-largest conifer genus, is a keystone component of the boreal and temperate dark-coniferous forests and harbors a remarkably large number of relict taxa. However, the uncertainty of the phylogenetic and biogeographic history of Abies significantly impedes our prediction of future dynamics and efficient conservation of firs. In this study, using 1,533 nuclear genes generated from transcriptome sequencing and a complete sampling of all widely recognized species, we have successfully reconstructed a robust phylogeny of global firs, in which four clades are strongly supported and all intersectional relationships are resolved, although phylogenetic discordance caused mainly by incomplete lineage sorting and hybridization was detected. Molecular dating and ancestral area reconstruction suggest a Northern Hemisphere high-latitude origin of Abies during the Late Cretaceous, but all extant firs diversified during the Miocene to the Pleistocene, and multiple continental and intercontinental dispersals took place in response to the late Neogene climate cooling and orogenic movements. Notably, four critically endangered firs endemic to subtropical mountains of China, including A. beshanzuensis, A. ziyuanensis, A. fanjingshanensis and A. yuanbaoshanensis from east to west, have different origins and evolutionary histories. Moreover, three hotspots of species richness, including western North America, central Japan, and the Hengduan Mountains, were identified in Abies. Elevation and precipitation, particularly precipitation of the coldest quarter, are the most significant environmental factors driving the global distribution pattern of fir species diversity. Some morphological traits are evolutionarily constrained, and those linked to elevational variation (e.g., purple cone) and cold resistance (e.g., pubescent branch and resinous bud) may have contributed to the diversification of global firs. Our study sheds new light on the spatiotemporal evolution of global firs, which will be of great help to forest management and species conservation in a warming world.

Identifying climate refugia for wild yaks (Bos mutus) on the Tibetan Plateau

Climate change is threatening fragile alpine ecosystems and their resident ungulates, particularly the wild yak (Bos mutus) that inhabits alpine areas between the tree line and glaciers on the Tibetan Plateau. Although wild yaks tend to shift habitats in response to changes in climatic factors, the precise impacts of climate change on their habitat distribution and climate refugia remain unclear. Based on over 1000 occurrence records, the maximum entropy (MaxEnt) algorithm was applied to simulate habitat ranges in the last glacial maximum (LGM), Mid-Holocene, current stage, and three greenhouse gas emission scenarios in 2070. Three habitat patches were identified as climate refugia for wild yaks that have persisted from the LGM to the present and are projected to persist until 2070. These stable areas account for approximately 64% of the current wild yak habitat extent and are sufficiently large to support viable populations. The long-term persistence of these climate refugia areas is primarily attributed to the unique alpine environmental features of the Tibetan Plateau, where relatively stable arid or semi-arid climates are maintained, and a wide range of forage resource supplies are available. However, habitat loss by 2070 caused by insufficient protection is predicted to lead to severe fragmentation in the southeastern and northwestern Kunlun, Hengduan, central-western Qilian, and southern Tanggula-northern Himalaya Mountains. Habitat disturbance has also been caused by increasing anthropogenic effects in the southern Tanggula and northern Himalaya Mountains. We suggest that sufficient protection, transboundary cooperation, and community involvement are required to improve wild yak conservation efforts. Our combined modeling method (MaxEnt-Zonation-Linkage Mapper-FRAGSTAT) can be utilized to identify priority areas and linkages between habitat patches while assessing the conservation efficiency of protected areas and analyzing the coupled relationship between climate change and anthropogenic impacts on the habitat distribution of endangered species.

Spatial patterns and environmental functions of dissolved organic matter in grassland soils of China

Soil dissolved organic matter (DOM) is crucial to atmospheric, terrestrial and aquatic environments as well as human life. Here, by characterizing DOM from 89 grassland soils throughout China, we reveal the spatial association between DOM geochemistry in the dry season vs annual ecosystem exchange and cancer cases. The humic-like and high molecular weight (3.4-25 kDa) fractions with lower biodegradability, decline from the northern to the southern regions of China, and are correlated with lower soil respiration and net ecosystem productivity at the continental scale. The <1.2 kDa and proteinaceous fractions could serve as a geographical indicator of nasopharyngeal cancer incidence and mortality, while the 3.4-25 kDa and humified fractions are potentially associated with pancreatic cancer cases (P < 0.05). Our findings highlight that exploiting the environmental functions of soil DOM and mitigating the negative impacts are necessary, and require actions tailored to local soil DOM conditions.

A dataset of topographic correction coefficients for shortwave downward radiation over the Pan-Third Pole

Prevalent Shortwave downward radiation (SWDR) estimates assume a flat surface, neglecting topographic effects and leading to significant errors in mountainous regions. We introduce SWDR topography correction coefficients (TCCs), based on the mountain radiative transfer model tailored for the Pan-Third Pole region. This dataset effectively bridges the disparities between flat-surface SWDR and rugged-surface SWDR, forming part of the Long-term Earth System spatiotemporally Seamless Radiation budget dataset (LessRad). Validation results using a three-dimensional radiative transfer model demonstrate the efficacy of this method in correcting solar direct radiation, sky diffuse radiation, and SWDR under diverse conditions. At a spatial resolution of 2.5 arc-minutes, the correction accuracy for solar direct radiation is characterized by a coefficient of determination (R²) of 0.998, a relative root mean square error (rRMSE) of 2.4%, and a relative bias (rbias) of 0.8%. For sky diffused radiation, an R² of 0.965, a rRMSE of 1.2%, and a rbias of -0.8%. SWDR corrections under clear and cloudy skies also show high accuracy, demonstrating the robustness of the TCCs approach.

Six years of high-resolution climatic data collected along an elevation gradient in the Italian Alps

The complex meso- and microclimatic heterogeneity inherent to mountainous regions, driven by both topographic and biotic factors, and the lack of observations, poses significant challenges to using climate models to predict and understand impacts at various scales. We present here a six-year dataset (2017-2022) of continuous climatic measurements collected at five elevations from 983 m to 2705 m above sea level in the Val Mazia - Matschertal valley in the Italian Alps. The measurements include the air temperature, relative humidity, wind speed and direction, solar radiation, soil properties, precipitation, and snow height. Collected within the European Long-Term Ecological Research program (LTER), this dataset is freely available in an open access repository. The time series may be valuable for the validation of regional climate models, atmospheric exchange modelling, and providing support for hydrological models and remote sensing products in mountain environments. Additionally, our data may be useful for research on the influence of elevation on ecological processes such as vegetation growth, plant composition, and soil biology. Beyond its utility in advancing such fundamental research, meteorological monitoring data contribute to informed socio-political decisions on climate adaptation strategies, land management, and water resource planning, enhancing the safety and resilience of mountain communities and biodiversity.

Precipitation input increases biodiversity of planktonic communities in the Qinghai-Tibet Plateau

Planktonic communities in aquatic ecosystems are crucial water quality indicators, with their growth dependent on runoff chemical and hydraulic characteristics (e.g., nutrient availability and turbidity). Previous studies have indicated that runoff components (i.e., proportions of precipitation, groundwater, snowmelt, etc.) play a vital role in regulating runoff characteristics, potentially affecting planktonic communities. However, the response of these communities to runoff components, particularly in mountainous regions, remains underexplored. In this study, we conducted four sampling campaigns from 2017 to 2020 in a watershed on the Qinghai-Tibet Plateau. Combined with laboratory incubation experiments, we examined the impact of various runoff components on the diversity and abundance of phytoplankton and zooplankton. We found that a higher proportion of precipitation in runoff contributed to an increase in the diversity of plankton communities. Laboratory experiments with unified water samples incubated with different runoff components demonstrated that the significant influence of precipitation on planktonic diversity primarily stems from the influx of abundant exogenous particulate material into rivers. Using a path analysis, we further confirmed that the impact of precipitation on diversity is primarily through chemical pathways, notably by increasing nutrient concentrations. Our study enhances our understanding of the interactions between the hydrological cycle and aquatic ecosystems, offering valuable insights for effectively maintaining and managing these natural environments.

Anthropogenic and biological activities elevate microplastics pollution in headwater ecosystem of Yangtze tributaries in Hindu Kush-Himalayan region

Microplastic (MP) pollution is widely spread in oceans, freshwater, and terrestrial environments but MPs in mountainous headwater ecosystem are rarely reported. This study focuses on the headwater of Yangtze tributaries of the Hindu Kush-Himalayan (HKH) region. Five streams at elevations of 900 to 3300 m were selected to investigate the distribution of MPs in water and sediments across altitudes. MPs were found in all water and sediment samples from top stream zone nearly in absence of anthropogenic activity, low anthropogenic zone, and high anthropogenic zone, increased from 12-54, 81-185 to 334-847 items/L, and 2-35, 26-84 to 124-428 items/kg, respectively. This elevation-dependent MP distribution indicated that as elevation decreased, anthropogenic activities intensified and increased MPs input and their abundance, size, and diversity. Notably, hydraulic projects, such as damming, were identified as potential barriers to the migration of MPs downstream. Microbiome analyses revealed the presence of bacterial genes associated with plastic biodegradation in all sediment samples. The study indicates that Shangri-la mountainous streams have been polluted with MPs for years with potential risk of generation of nano-sized particles via natural fragmentation and biodegradation, and thus raises concern on MPs pollution in headwaters streams in mountainous regions.

Understanding the Asian water tower requires a redesigned precipitation observation strategy

The Asian water tower (AWT) serves as the source of 10 major Asian river systems and supports the lives of ~2 billion people. Obtaining reliable precipitation data over the AWT is a prerequisite for understanding the water cycle within this pivotal region. Here, we quantitatively reveal that the "observed" precipitation over the AWT is considerably underestimated in view of observational evidence from three water cycle components, namely, evapotranspiration, runoff, and accumulated snow. We found that three paradoxes appear if the so-called observed precipitation is corrected, namely, actual evapotranspiration exceeding precipitation, unrealistically high runoff coefficients, and accumulated snow water equivalent exceeding contemporaneous precipitation. We then explain the cause of precipitation underestimation from instrumental error caused by wind-induced gauge undercatch and the representativeness error caused by sparse-uneven gauge density and the complexity of local surface conditions. These findings require us to rethink previous results concerning the water cycle, prompting the study to discuss potential solutions.

How and when glacial runoff is important: Tracing dynamics of meltwater and rainfall contribution to river runoff from headwaters to lowland in the Caucasus Mountains

As glacier degradation is intensifying worldwide, understanding how and when glacial runoff is important becomes imperative for economic planning and societal adaptation in response to climate change. This research highlights a probable emergence of new low-flow periods, ranging from one to several weeks, with an anticipated 50-90 % reduction in runoff even in major rivers originating in glacierized mountains by the mid to late 21th century. While the predicted decline in annual and monthly runoff appears moderate for most glaciated regions globally, the emergence of new deglaciation-induced summer low flow periods could create critical "bottle necks" constraining effective water resources management. In this study, a nested catchment approach (7.6-2259 km2) in conjunction with an isotopic tracer method (D, 18O), was employed to quantify the seasonal dynamics of snow and glacial meltwater and rainfall contribution to runoff across various scales of river catchments for the underreported Caucasus Mountains. Although the contribution of meltwater was predictably dominant in the headwaters (75-100 %), it still constituted a substantial 50-60 % of river runoff in the lower reaches most of the time from June to September. While the relative capacity for rainwater storage was found to significantly increase with watershed scale, during weeks devoid of noteworthy rainfall, the runoff in river basins with a mere 7 % glaciation basically entirely consists of what is formed in the glacierized headwaters. The glacial runoff was prevalent in the melt component from late July/early August to mid-September: not less than 30-60 % to the total runoff in the headwaters and 30-40 % in the lower reaches. An approach is proposed to account for the spatial heterogeneity of stable water isotopic content within snow cover and glacier ice. Sources of uncertainties and soundness of assumptions typically used for isotopic hydrograph separation are discussed with particular consideration given to the study objectives.

Escalating Carbon Export from High-Elevation Rivers in a Warming Climate

High-elevation mountains have experienced disproportionately rapid warming, yet the effect of warming on the lateral export of terrestrial carbon to rivers remains poorly explored and understood in these regions. Here, we present a long-term data set of dissolved inorganic carbon (DIC) and a more detailed, short-term data set of DIC, δ13CDIC, and organic carbon from two major rivers of the Qinghai-Tibetan Plateau, the Jinsha River (JSR) and the Yalong River (YLR). In the higher-elevation JSR with ∼51% continuous permafrost coverage, warming (>3 °C) and increasing precipitation coincided with substantially increased DIC concentrations by 35% and fluxes by 110%. In the lower-elevation YLR with ∼14% continuous permafrost, such increases did not occur despite a comparable extent of warming. Riverine concentrations of dissolved and particulate organic carbon increased with discharge (mobilization) in both rivers. In the JSR, DIC concentrations transitioned from dilution (decreasing concentration with discharge) in earlier, colder years to chemostasis (relatively constant concentration) in later, warmer years. This changing pattern, together with lighter δ13CDIC under high discharge, suggests that permafrost thawing boosts DIC production and export via enhancing soil respiration and weathering. These findings reveal the predominant role of warming in altering carbon lateral export by escalating concentrations and fluxes and modifying export patterns.

Decreasing trends of mean and extreme snowfall in High Mountain Asia

Intense warming profoundly alters precipitation phase patterns and intensity in High Mountain Asia (HMA). While snowfall climatology and precipitation extremes have been studied, there is a lack of understanding of snowfall extremes within HMA. Here, we investigate the spatial and temporal variability of non-extreme and extreme snowfall in hydrological years 1979-2020 using multi-source meteorological data, compare weather systems during extreme and non-extreme snowfall events, and identify key circulation factors that influence fluctuations in mean annual snowfall and extreme snowfall. The snowfall amount (-0.13 d/mm), days (-0.56 d/a), and fraction (-0.0012) were significantly reduced in HMA, with a shorter snowfall season (-0.52 d/a). Some extreme snowfall metrics (maximum 1-day snowfall and maximum 3-day snowfall) were insensitive to climate change, whereas the maximum consecutive snowfall days (-0.007 d/a), snowfall amount (-0.0023 mm/a), heavy snowfall days (S95pD; 0.0087 d/a), and extremely heavy snowfall days (S99pD; -0.1019 d/a) showed significant decreases. Synthetic analyses show that extreme snowfall events were more likely to occur within a narrow temperature range (-5 °C to 3 °C) with higher relative humidity and precipitation compared to non-extreme events. A stepwise regression method was used to determine that the fluctuation in the average annual snowfall was closely related to the Atlantic Multidecadal Oscillation, whereas the variation in extreme snowfall was mainly influenced by the Southern Oscillation Index. Our research provides a reference for assessing the potential impacts of climate change on a regional scale for risk management and disaster adaptation.

Significant role of permafrost in regional hydrology of the Upper Indus Basin, India

Upper Indus Basin (UIB), being climatologically sensitive and socio-economically important, has emerged as a hotspot for eco-hydrological studies. Permafrost, one of the essential components of the regional hydrological cycle with a critical role in microclimate, is also an important water resource in the UIB. Despite being an important component of the cryospheric system, permafrost is least studied in the UIB. In present study, we used stable oxygen and hydrogen isotopic composition in supra-permafrost water (SPFW) and aufeis along with precipitation, snowpack, glacier and other groundwaters to assess their variability and estimate their contribution to regional hydrology. The sources are evolving isotopically, depending on physiographic and hydrometeorological factors, with each source attaining different (if not distinct) isotopic signatures. The isotopic signatures (with different ranges) of sources help in estimating the contribution from these sources. A significant altitude gradient of δ18O is observed in stream water, SPFW and other groundwaters. Isotopic composition in SPFW is differentially modulated by fractionation, resulting in isotopic variability from the source waters. The results suggest snowmelt and/or glacier melt as the source of SPFW. To stream flow, SPFW is the dominant contributor (43 ± 18 %) at higher elevations (> 4300 m a.m.s.l.) in July, followed by snowmelt (26 ± 10 %). In September, SPFW contribution decreases (14 ± 8 %), but the contribution from other groundwaters becomes dominant (39 ± 11 %) to stream flow. The results indicate the significant role of seasonal thawing and freezing of active layer on the contribution from SPFW. This study highlights the significant role of permafrost in the hydrological system of the basin. The study also emphasizes the need to understand the dynamics of permafrost, taliks of various types (e.g., supra-permafrost subaerial talik) and active layer under changing climate to define the subsequent implications to regional hydrology, eco-hydrological systems and micro-climate of permafrost regions.

Treeline displacement may affect lake dissolved organic matter processing at high latitudes and altitudes

Climate change induced shifts in treeline position, both towards higher altitudes and latitudes induce changes in soil organic matter. Eventually, soil organic matter is transported to alpine and subarctic lakes with yet unknown consequences for dissolved organic matter (DOM) diversity and processing. Here, we experimentally investigate the consequences of treeline shifts by amending subarctic and temperate alpine lake water with soil-derived DOM from above and below the treeline. We use ultra-high resolution mass spectrometry (FT-ICR MS) to track molecular DOM diversity (i.e., chemodiversity), estimate DOM decay and measure bacterial growth efficiency. In both lakes, soil-derived DOM from below the treeline increases lake DOM chemodiversity mainly through the enrichment with polyphenolic and highly unsaturated compounds. These compositional changes are associated with reductions in bulk and compound-level DOM reactivity and reduced bacterial growth efficiency. Our results suggest that treeline advancement has the potential to enrich a large number of lake ecosystems with less biodegradable DOM, affecting bacterial community function and potentially altering the biogeochemical cycling of carbon in lakes at high latitudes and altitudes.

Warming affects leaf light use efficiency and functional traits in alpine plants: evidence from a 4-year in-situ field experiment

Introduction

Light use efficiency (LUE) is a crucial determinant of plant productivity, while leaf functional traits directly affect ecosystem functions. However, it remains unclear how climate warming affects LUE and leaf functional traits of dominant species in alpine meadows.

Methods

We conducted a 4-year in-situ field warming experiment to investigate the eco-physiological characteristics for a dominant species (Elymus nutans) and a common species (Potentilla anserina) on the Tibetan Plateau. The leaf traits, photosynthesis and fluorescence characteristics were measured, along with the soil physical-chemical properties associated with the two species.

Results and discussions

Experimental warming increased the leaf LUE, maximum photochemical efficiency, non-photochemical quenching, relative water content and specific leaf area for both species. However, there was a decrease in leaf and soil element content. Different species exhibit varying adaptability to warming. Increasing temperature significantly increased the photosynthetic rate, stomatal conductance, transpiration rate, total water content, and specific leaf volume of E. nutans; however, all these traits exhibited an opposite trend in P. anserina. Warming has a direct negative impact on leaf LUE and an indirectly enhances LUE through its effects on leaf traits. The impact of warming on plant photosynthetic capacity is primarily mediated by soil nutrients and leaf traits. These results indicate that the two different species employ distinct adaptive strategies in response to climate change, which are related to their species-specific variations. Such changes can confer an adaptive advantage for plant to cope with environmental change and potentially lead to alterations to ecosystem structure and functioning.

Aerosol forcing regulating recent decadal change of summer water vapor budget over the Tibetan Plateau

The Tibetan Plateau (TP), known as the Asian water tower, has been getting wetter since the 1970s. However, the primary drivers behind this phenomenon are still highly controversial. Here, we isolate the impacts of greenhouse gases (GHG), aerosols, natural forcings and internal climate variability on the decadal change of summer water vapor budget (WVB) over the TP using multi-model ensemble simulations. We show that an anomalous Rossby wave train in the upper troposphere travelling eastward from central Europe and equatorward temperature gradient in eastern China due to the inhomogeneous aerosol forcing in Eurasia jointly contribute to anomalous easterly winds over the eastern TP. Such anomalous easterly winds result in a significant decrease in water vapor export from the eastern boundary of the TP and dominate the enhanced summer WVB over the TP during 1979-2014. Our results highlight that spatial variation of aerosol forcing can be used as an important indicator to project future WVB over the TP.

The Impact of Climate Change, Pollution, and Biodiversity Loss on Digestive Health and Disease

The environment is changing rapidly under pressure from 3 related drivers: climate change, pollution, and biodiversity loss. These environmental changes are affecting digestive health and disease in multiple ways. Heat extremes can cause intestinal and hepatic dysfunction. Access to adequate amounts of food of high nutritional content and to clean water is under threat. Extreme weather is associated with flooding and enteric infections and affects the delivery of care through infrastructure loss. Air, water, and soil pollution from chemicals and plastics are emerging as risk factors for a variety of intestinal diseases including eosinophilic esophagitis, metabolic dysfunction associated fatty liver disease, digestive tract cancers, inflammatory bowel disease, and functional bowel disease. Migration of populations to cities and between countries poses a special challenge to the delivery of digestive care. The response to the threat of environmental change is well underway in the global digestive health community, especially with regard to understanding and reducing the environmental impact of endoscopy. Individuals, and peer societies, are becoming more engaged, and have an important role to play in meeting the challenge.

Estimation of spatial distribution of soil moisture on steep hillslopes by state-space approach (SSA)

Soil moisture is a critical variable that quantifies precipitation, floods, droughts, irrigation, and other factors with regard to decision-making and risk evaluation. An accurate prediction of soil moisture dynamics is important for soil and environmental management. However, the complex topographic condition and land use in hilly and mountainous areas make it a challenge to monitor and predict soil moisture dynamics in these areas. In this study, the determinants of soil moisture variability were determined by structural equation modeling, and then an attempt was made to estimate the spatial distribution of soil moisture content on steep hillslope using the state-space method. Herein, soil moisture at different depths (0-10, 10-20, and 20-30 cm) was monitored by portable time-domain reflectometer (TDR) along this hillslope (100 m × 180 m). It showed that the spatial variability of soil moisture decreased with increasing soil wetness, primarily in the topsoil (0-10 cm). Soil moisture was correlated with elevation (r = 0.28, 0.50, and 0.28), capillary porosity (r = 0.06, 0.37, and 0.28), soil texture (r for Clay: 0.20, 0.24, and 0.16; r for Sand: -0.25, -0.18, and -0.28), organic carbon (r = -0.31, -0.08, and 0.10) and land use (r = -0.01, 0.28, and 0.24) under different conditions (dry, moderate, and wet). Among these determinants, elevation made direct contributions to soil moisture variation, especially under moderate conditions, while land use made its impacts by altering soil texture. It is encouraging that the state-space approach yielded precise and cost-effective predictions of soil moisture dynamics along this steep hillslope since it gives the minimum root-mean-square error (RMSE) and Akaike information criterion (AIC). Moreover, soil organic carbon (AIC = -4.497, RMSE = 0.104, R2 = 0.899), rock fragment contents (AIC = -4.366, RMSE = 0.111, R2 = 0.878), and elevation (AIC = -3.693, RMSE = 0.156, R2 = 0.629) effectively anticipated the spatial distribution of soil moisture under dry, moderate, and wet conditions, respectively. This study confirms the efficacy of the state-space approach as a valuable tool for soil moisture prediction in areas characterized by complex and spatially heterogeneous conditions.

Dynamic changes in water resources and comprehensive assessment of water resource utilization efficiency in the Aral Sea basin, Central Asia

The Aral Sea Basin in Central Asia faces significant challenges in improving water utilization and treatment because of frequent transboundary river water disputes and shortages of water resources. However, the traditional water resource utilization efficiency (WRUE) assessment models generally have the defect of over-validating evaluation results. To solve this problem, this study used the Coefficient of Variation method to constrain the self-contained weights in the traditional Data Envelopment Analysis (DEA) to construct an improved CV-DEA model, and assessed the WRUE of the Aral Sea Basin countries during 2000-2018 and compared the WRUE with that of the countries in the Mekong River Basin and Northeast Asia, then explored the factors influencing water utilization. The conclusions were drawn: since 1960, the runoff from the upper Amu Darya and Syr Darya rivers increased significantly, while the runoff from the lower Amu Darya River into the Aral Sea declined. Meanwhile, the water area of the Aral Sea shrank from 2.56 × 104 km2 to 0.70 × 104 km2 in 2000-2018, with the Northern Aral Sea remaining stable while the southern part shrinking sharply. The WRUE of the Aral Sea Basin (0.599, on average) was higher than that of the Mekong River Basin (0.547) and lower than that of Northeast Asia (0.885). Kazakhstan and Uzbekistan had the highest WRUE of 0.819 and 0.685 respectively, and the WRUE in both two countries improved from 2000 to 2018. Tajikistan (0.495) and Turkmenistan (0.402) experienced decreases in WRUEs. The high input redundancy of agricultural water consumption was the main driving force affecting WRUE in the basin.

Assessing size shifts amidst a warming climate in lakes recharged by the Asian Water Tower through satellite imagery

Recent studies indicate that the Asian Water Tower (AWT) is at risk due to climate change, which can negatively impact water and food security in Asia. However, there is a lack of comprehensive information on lakes' spatial and temporal changes in this region. This information is crucial for understanding the risk magnitude and designing strategies. To fill this research gap, we analyzed 89,480 Landsat images from 1977 ± 2 to 2020 ± 2 to investigate the changes in the size of lakes recharged by the AWT. Our findings showed that out of the 209 lakes larger than 50 km2, 176 (84 %) grew during the wet season and 167 (81 %) during the dry season. 74 % of expanded lakes are located in the Inner Tibetan Plateau (TP) and Tarim basins. The lakes that shrank are found mainly in the Helmand, Indus, and Yangtze basins. Over the entire period, the area of shrinkage (55,077.028 km2 in wet season, 53,986.796 km2 in dry) markedly exceeded expansion (13,000.267 km2 in wet, 11,038.805 km2 in dry), with the drastic decline of the Aral Sea being a major contributor to shrinkage, accounting for 90 % of the total loss. From 1990 ± 2 to 2020 ± 2, alpine lakes mostly expanded, plain lakes mostly shrank, with the opposite trend from 1977 ± 2 to 1990 ± 2. Glacial loss and permafrost thawing under global warming in the Inner TP, Tarim Interior, Syr Darya, and Mekong basins were strongly correlated with lake expansion. However, permafrost discontinuities may prevent significant growth of lakes in the Indus and Ganges basins despite increased recharge. Our findings point to the prominence of the risk the lakes recharged by AWT face. Taking immediate action to manage these risks and adaptation is crucial as the AWT retreats and lake recharges are slowed.

Sand fixation and human activities on the Qinghai-Tibet Plateau for ecological conservation and sustainable development

The sand fixation ecosystem services and human activities on the Qinghai-Tibet Plateau (QTP) play a crucial role in local sustainable development and ecosystem health, with significant implications for surrounding regions and the global ecological environment. We employed an improved integrated wind erosion modeling system (IWEMS) model for the QTP to simulate sand fixation quantities under the unique low temperature and low pressure conditions prevalent on the plateau. Using the human footprint index (HFI), the intensity of human activities on the plateau was quantified. Additionally, an econometric model was constructed to analyze the impacts of the natural factors, the HFI, and policy factors on the sand fixation capacity. The results revealed that the average sand fixation quantity was 1368.0 t/km2/a, with a standard deviation of 1725.4 t/km2/a, and the highest value during the study period occurred in 2003. The average value of the HFI for 2020 was 6.69 with a standard deviation of 6.61, and the HFI exhibited a continuous growth trend from 2000 to 2020. Despite this growth, the average human activity intensity remained at a low level, with over 50 % of the area having an index value of <4.84. Overall, a strong negative correlation was observed between the sand fixation ecological capacity and the HFI on the QTP. However, extensive regions exhibited high values or low values for both indicators. The sand fixation capacity on the QTP is influenced by both natural and human factors. In light of these findings, suggestions are made for optimizing protected area design, rational control of human activity scales, and targeted human activity aggregation within certain regions as part of ecological conservation strategies. This study has implications for assessing sand fixation ecological functions in high-altitude regions and enhancing sand fixation capacity within the region, providing valuable practical guidance.

Imbalance in lake variability but not embodying driving factors on the Qinghai-Tibetan Plateau calls on heterogeneous lake management

Comprehensive regional remote analysis tends to neglect lakes in exorheic basins on the Qinghai-Tibetan Plateau (QTP), and a concurrent lack of discussions on whether there exist imbalanced explanations for the driving forces of both internal and external lakes is also present. We integrate multisourced lake datasets, high-resolution information, and available altimetry datasets to establish multiple mathematical models to meta-simulate lake volume changes, extend current lake variation datasets, and quantify the imbalance of variations and factors driving the water mass budget. The results showed that the primary cause of lake variations in QTP is net precipitation (57.75 ± 31.46%), followed by glacier runoff (33.53 ± 31.42%), and permafrost (8.34 ± 7.87%). Even though glacier runoff is currently considered as a weak factor of lake variation, heterogeneous results call for remaining attention in glacier-induced lake basins. Imbalance embodying in lake variability but not in contributions of driving factors, which calls for special lake management ways in different watersheds.

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.

Impacts of climate change on the fate of contaminants through extreme weather events

The direct impacts of climate change involve a multitude of phenomena, including rising sea levels, intensified severe weather events such as droughts and flooding, increased temperatures leading to wildfires, and unpredictable fluctuations in rainfall. This comprehensive review intends to examine firstly the probable consequences of climate change on extreme weather events such as drought, flood and wildfire. This review subsequently examines the release and transformation of contaminants in terrestrial, aquatic, and atmospheric environments in response to extreme weather events driven by climate change. While drought and flood influence the dynamics of inorganic and organic contaminants in terrestrial and aquatic environments, thereby influencing their mobility and transport, wildfire results in the release and spread of organic contaminants in the atmosphere. There is a nascent awareness of climate change's influence of climate change-induced extreme weather events on the dynamics of environmental contaminants in the scientific community and decision-making processes. The remediation industry, in particular, lags behind in adopting adaptive measures for managing contaminated environments affected by climate change-induced extreme weather events. However, recognizing the need for assessment measures represents a pivotal first step towards fostering more adaptive practices in the management of contaminated environments. We highlight the urgency of collaboration between environmental chemists and climate change experts, emphasizing the importance of jointly assessing the fate of contaminants and rigorous action to augment risk assessment and remediation strategies to safeguard the health of our environment.

Metagenomic analysis of antibiotic-resistance genes and viruses released from glaciers into downstream habitats

Glaciers serve as effective reservoirs of antibiotic resistance genes (ARGs) and viruses for millions of years. Climate change and anthropogenic activity have accelerated the melting of glaciers, but the patterns of release of ARGs and viruses from melting glaciers into downstream habitats remain unknown. We analyzed 171 metagenomic samples from glaciers and their downstream habitats and found that the abundance and diversity of ARGs were higher in glaciers (polar and plateau glaciers) than downstream habitats (Arctic Ocean, Qinghai Lake, and Yangtze River Basin), with the diversity of viruses having the opposite pattern. Proteobacteria and Actinobacteria were the main potential hosts of ARGs and viruses, and the richness of ARGs carried by the hosts was positively correlated with viral abundance, suggesting that the transmission of viruses in the hosts could disseminate ARGs. Source tracking indicated that >18 % of the ARGs and >25 % of the viruses detected in downstream habitats originated from glaciers, demonstrating that glaciers could be one of the potential sources of ARGs and viruses in downstream habitats. Increased solar radiation and emission of carbon dioxide mainly influenced the release of the ARGs and viruses from glaciers into downstream habitats. This study provides a systematic insight demonstrating the release of ARGs and viruses from the melting glaciers, potentially increasing ecological pressure.

Evidence of human influence on Northern Hemisphere snow loss

Documenting the rate, magnitude and causes of snow loss is essential to benchmark the pace of climate change and to manage the differential water security risks of snowpack declines1-4. So far, however, observational uncertainties in snow mass5,6 have made the detection and attribution of human-forced snow losses elusive, undermining societal preparedness. Here we show that human-caused warming has caused declines in Northern Hemisphere-scale March snowpack over the 1981-2020 period. Using an ensemble of snowpack reconstructions, we identify robust snow trends in 82 out of 169 major Northern Hemisphere river basins, 31 of which we can confidently attribute to human influence. Most crucially, we show a generalizable and highly nonlinear temperature sensitivity of snowpack, in which snow becomes marginally more sensitive to one degree Celsius of warming as climatological winter temperatures exceed minus eight degrees Celsius. Such nonlinearity explains the lack of widespread snow loss so far and augurs much sharper declines and water security risks in the most populous basins. Together, our results emphasize that human-forced snow losses and their water consequences are attributable-even absent their clear detection in individual snow products-and will accelerate and homogenize with near-term warming, posing risks to water resources in the absence of substantial climate mitigation.

Spatial characteristics of hydrochemistry and stable isotopes in river and groundwater, and runoff components in the Shule River Basin, Northeastern of Tibet Plateau

Water resources play a crucial role in constraining the high-quality development of the arid, necessitating an in-depth investigation and understanding of hydrological processes, hydrochemical characteristics, and their influencing factors amidst climate change. This study meticulously examined and analyzed the hydrochemistry and stable isotope composition (δ18O and δD) of river and groundwater within the Shule River Basin (SRB). Results showed that both river (mean: 8.01) and groundwater (mean: 7.92) had alkaline pH values, while average total dissolved solids were measured at 709.25 mg/L in river and 861.88 mg/L in groundwater, indicating predominance of fresh water sources. HCO3-, SO42-, Na+ and Ca2+ were the most abundant ions, influenced by evaporation-crystallization processes and rock weathering. The dominated hydrochemical facies in both river and groundwater were Ca-HCO3 type in the upper (UR) and the middle reaches (MR), while Ca-Mg-Cl type in the lower reaches (LR). The local meteoric water line (LMWL) was defined as δD = 8.01δ18O + 18.48 (R2 = 0.98, n = 163; P < 0 0.001). The more negative δ18O and δD values in river and groundwater were plotted nearby and lower right of the LMWL, implying that the important recharge source of those waters is from precipitation. The relationship between river δ18O and elevation showed an increase of 0.14‰/100 m in the UR, but a negative correlation with a rate of -0.47‰/100 m in the MR and LR. Precipitation, groundwater, baseflow and meltwater accounted for 62.5%, 19.8%, 11.9% and 5.8% of the UR river, respectively, during the observed period, according to the end-member mixing analysis. These runoff components displayed distinct seasonal variations, primarily driven by precipitation during the early and groundwater/baseflow during the rapid and end-stage ablation periods. The observed alterations in hydrological elements present both opportunities and challenges for water resource management across the SRB, and adaptive measures have been proposed based on our study. These findings provide valuable insights into efficient utilization of water resources from water chemistry and environmental isotopes.

A landscape persistence-based methodological framework for assessing ecological stability

Ecological stability is a critical factor in global sustainable development, yet its significance has been overlooked. Here we introduce a landscape-oriented framework to evaluate ecological stability in the Qingzang Plateau (QP). Our findings reveal a medium-high stability level in the QP, with minimal changes over recent years. The driving factors vary across landscape types, with climate and anthropogenic factors emerging as crucial determinants. While anthropogenic factors are strong but unstable due to policy changes and economic development, climatic factors exert a consistent influence. Based on our results, we propose site-specific ecological conservation and restoration measures. The ecological stability assessment framework provides a practical tool to understand the link between environmental conditions and ecosystems.

Early-Middle Holocene high lake levels of Rinqen Shubtso on the southern Tibetan Plateau and the formation mechanisms

The lake-level highstands on the southern Tibetan Plateau (TP) during the Early-Middle Holocene have traditionally been attributed to increased monsoonal precipitation. However, there has been limited discussion and evaluation regarding how the elevated shoreline indicates the formation of mega-paleolakes and the effects of glacial meltwater on rising lake levels. In this study, we conducted an investigation into the well-preserved paleoshorelines of Rinqen Shubtso, a closed-basin lake system located on the southern TP. By utilizing 14C dating and analyzing shoreline elevations, the Holocene lake-level fluctuation history of Rinqen Shubtso was reconstructed. Through examining strontium (87Sr/86Sr) and oxygen isotopes (δ18O), as well as Rb/Sr ratios in tufa samples from the shoreline, we evaluated the relative contribution of glacial meltwater and East Asian Monsoon precipitation to the lake-level expansion throughout this period. Our findings indicate that prior to 8.5 cal ka BP, the lake level reached its highest elevation before experiencing a rapid drop by approximately 44 m within a short timeframe. Subsequently, maintaining a stable highstand between 8.5 and 5.8 cal ka BP before gradually declining to its present elevation thereafter. We argue that the glacial meltwater induced by rising temperature due to solar insolation likely played a significant role in contributing to these large amplitude high lake levels prior to 8.5 cal ka BP, whereas the maximum East Asian Monsoon precipitation was responsible for sustaining high water levels during 8.5-5.8 cal ka BP when the mean latitudinal position of the summer Intertropical Convergence Zone shifted northward until reached its northernmost point at 8.5 cal ka BP. Following 5.8 cal ka BP, with the weakening of summer monsoon precipitation observed, gradually decreased lake level occurred accordingly. Our results provide valuable insights into understanding past changes in lake level, which are of great importance to predicting future lake variations on the TP.

Identifying snowfall elevation patterns by assimilating satellite-based snow depth retrievals

Precipitation in mountain regions is highly variable and poorly measured, posing important challenges to water resource management. Traditional methods to estimate precipitation include in-situ gauges, Doppler weather radars, satellite radars and radiometers, numerical modeling and reanalysis products. Each of these methods is unable to adequately capture complex orographic precipitation. Here, we propose a novel approach to characterize orographic snowfall over mountain regions. We use a particle batch smoother to leverage satellite information from Sentinel-1 derived snow depth retrievals and to correct various gridded precipitation products. This novel approach is tested using a simple snow model for an alpine basin located in Trentino Alto Adige, Italy. We quantify the precipitation biases across the basin and found that the assimilation method (i) corrects for snowfall biases and uncertainties, (ii) leads to cumulative snowfall elevation patterns that are consistent across precipitation products, and (iii) results in overall improved basin-wide snow variables (snow depth and snow cover area) and basin streamflow estimates.

Projected changes in soil freeze depth and their eco-hydrological impacts over the Tibetan Plateau during the 21st century

In the context of global warming, the soil freeze depth (SFD) over the Tibetan Plateau (TP) has undergone significant changes, with a series of profound impacts on the hydrological cycle and ecosystem. The complex terrains and high elevations of the TP pose great challenges in data acquisition, presenting difficulties for studying SFD in this region. This study employs Stefan's solution and downscaled datasets from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to simulate the future SFDs over the TP. The changing trends of the projected SFDs under different Shared Socio-economic Pathways (SSP) scenarios are investigated, and; the responses of SFDs to potential climatic factors, such as temperature and precipitation, are analyzed. The potential impacts of SFD changes on eco-hydrological processes are analyzed based on the relationships between SFDs, the distribution of frozen ground, soil moisture, and the Normalized Difference Vegetation Index (NDVI). Results show that the projected SFDs of the TP are estimated to decrease at rates of 0.100 cm/yr under the SSP126, 0.330 cm/yr under the SSP245, 0.565 cm/yr under the SSP370, and 0.750 cm/yr under the SSP585. Additionally, the SFD decreased at a rate of 0.160 cm/yr during the historical period from 1950 to 2014, which was between the decreasing rates of the SSP126 and SSP245 scenarios. The projected SFDs are negatively correlated with air temperature and precipitation, more significant under the higher emissions scenario. The projected decrease in SFDs will significantly impact eco-hydrological processes. A rapid decrease in SFD may lead to a decline in soil moisture content and have adverse impacts on vegetation growth. This research provides valuable insights into the future changes in SFD on the TP and their impacts on eco-hydrological processes.

How to synergize ecological restoration to co-benefit the beneficial contributions of nature to people on the Qinghai-Tibet Plateau?

Understanding the magnitude and spatial distribution of ecological restoration requires a precise assessment of the beneficial contributions of nature to people. However, where the restoration areas should be located and whether the natural contribution of a compensation area can satisfy people's needs in the context of ecological degradation remain unclear. To address these issues, we selected the Qinghai-Tibet Plateau as the study areas, utilizing the offset portfolio analyzer and locator model to identify the compensation sites that offset the losses of ecosystem services and biodiversity resulting from ecological degradation. These compensation sites were developed through two offset types: restoration and protection. Then, based on the offset sites, we assessed nature's contribution to people (NCP) under the current status and future scenarios in terms of various aspects, including the habitat (NCP1), climate change (NCP4), and water quantity and flow regulation (NCP6). This study found that the area impacted by agricultural development was 7.15 × 105 ha, and the required compensation area was 5.5 × 106 ha under the current status. The ratio of the impacted area to the required area was approximately 7.0 in the future scenarios. The average habitat qualities were 0.14 and 0.30, while the mean NCP1 values were 2.69 and 0.51 in the protection and restoration offset sites, respectively. Moreover, based on the offset sites, the high-value contributions in NCP4 accounted for 18.64%-22.69% and 38.87%-46.17% of the total offset sites in terms of the restoration and protection offset types, respectively. Additionally, the estimated high-value contributions in NCP6 accounted for 58.35%-59.02% and 84.40%-95.86% of the total offset sites in the restoration and protection offset types, respectively. Our findings highlighted the significance of ecological restoration in showcasing the role of NCPs. These results could aid conservation managers in developing more targeted ecological strategies to enhance human well-being.

Enhanced glacial lake activity threatens numerous communities and infrastructure in the Third Pole

Glacial lake outburst floods (GLOFs) are among the most severe cryospheric hazards in the Third Pole, encompassing the Tibetan Plateau and surrounding Himalayas, Hindu Kush, and Tianshan Mountains. Recent studies on glacial lake changes and GLOF characteristics and risks in this region have shown scattered and insufficiently detailed features. Here, we conduct an appraisal of the GLOF risks by combining high-resolution satellite images, case-by-case high-precision GLOF modeling, and detailed downstream exposure data. The glacial lake changes from 2018 to 2022 in the region were primarily driven by the accelerated expansion of proglacial lakes. The GLOF frequency has exhibited a significant increasing trend since 1980, with intensified activity in Southeastern Tibet and the China-Nepal border area over the past decade. Approximately 6,353 km2 of land could be at risk from potential GLOFs, posing threats to 55,808 buildings, 105 hydropower projects, 194 km2 of farmland, 5,005 km of roads, and 4,038 bridges. This study directly responds to the need for local disaster prevention and mitigation strategies, highlighting the urgent requirement of reducing GLOF threats in the Third Pole and the importance of regional cooperation.

Climate change impacts on groundwater discharge-dependent streamflow in an alpine headwater catchment

Climate change will have-and, in much of the world, is already having-a pronounced impact on alpine water resources. A deeper understanding of the future role of groundwater in alpine catchments, including quantification of climate change impacts on groundwater discharge, is vital for understanding the future of alpine water resources as a whole. Here, we develop and couple a geophysics-informed groundwater model with a net recharge model to investigate the impacts of climate change on a nival-regime alpine headwater catchment with significant unconfined Quaternary aquifer coverage. Flow in the groundwater-fed stream at the catchment outlet is analysed to determine changes in its annual dynamics. Comparing the periods 2020-2040 and 2080-2100 under ten RCP-8.5 climate models, we find a 35 % decrease in mean groundwater discharge and an increase in no-flow periods from ~0 % to 4.3 %. We also observe significant changes to the timing of monthly mean discharge maxima and minima, which shift ~1 month and ~5 months earlier, respectively. While groundwater has the potential to dampen the impacts of snow cover loss, currently perennial nival-regime alpine streams could be at risk of becoming intermittent by the end of the century. Our study underscores the increasingly critical role that groundwater will play in alpine catchments and emphasizes the need for quantitative understanding of the limits to its buffering capacity.

Canada Source Watershed Polygons (Can-SWaP): A dataset for the protection of Canada's municipal water supply

Over 80% of municipal (i.e., excluding industrial and agricultural) water use in Canada comes from streams, lakes, and reservoirs. These freshwater bodies and their catchments require adequate protection to secure drinking water supply for Canadians. Canada, like most countries, lacks a consolidated national dataset of municipal catchments, arguably due to gaps in data availability. Against this backdrop, we present the Canada Source Watershed Polygons dataset, or Can-SWaP. Can-SWaP was created using point locations of more than 3,300 municipal water licences defining rights to surface water withdrawal. Where possible, the resulting 1,574 catchments were assessed for accuracy in spatial coverage against provincial and local datasets. Each watershed in Can-SWaP has an estimated water volume used for municipal water purposes derived from licencing data, and several variables from RiverATLAS for investigating the integrity of surface drinking water sources in Canada. Furthermore, basing our method on the HydroSHEDS suite of global products offers a robust framework for the production of other national datasets following an established international standard.

Establishing a quantitative assessment methodology framework of water conservation based on the water balance method under spatiotemporal and different discontinuous ecosystem scales

Water conservation (WC) is an essential terrestrial ecosystem service that mitigates surface runoff and replenishes groundwater, which has received considerable attention under the dual pressures of climate change and human activity. However, there is insufficient understanding of the trends in WC changes on temporal (annual, monthly, daily), spatial, and ecosystem scales. This study proposed a quantitative assessment methodology framework (QAMF) for analyzing the spatiotemporal variation of WC under different discontinuous ecosystems. The QAMF mainly used models and methods such as the hydrological model (SWAT), calibration and uncertainty program (SWAT-CUP), WC calculation formula (water balance method), and spatial analysis method (empirical orthogonal function and wavelet analysis). It was applied to the source region of the Yellow River (SRYR), where the ecological landscape pattern underwent varying degrees of degradation, and WC capacity decreased. The results show that: Firstly, the constructed SWAT in the SRYR had high accuracy, and the proposed formula for calculating WC was suitable for multi-temporal scale analysis of WC in spatially distributed discontinuous basins. Secondly, the annual and monthly WC were respectively 81.00-184.13 mm and -28.58-107.64 mm, and daily WC was positive during extreme precipitation periods and negative during dry periods. The regulating effect of WC was fully reflected on the daily scale, partially reflected on the monthly scale, and absent on the annual scale. Third, the crucial WC area was mainly distributed in the southeast, and there was a significant primary yearly cycle of WC in the SRYR. Finally, different ecosystems exhibited different WC capabilities, and protecting the diversity of ecosystems played an essential role in maintaining and improving the WC function in the SRYR. This project has great scientific significance and technological support for scientifically evaluating the WC capacity in the SRYR.

Historical and projected evolutions of glaciers in response to climate change in High Mountain Asia

Glacier changes are regarded as the conspicuous icon of climate change in High Mountain Asia (HMA) alpine environments. Multi-temporal glacier coverage is essential for mass balance estimations and understanding glacial changes in response to climate variability. However, consistent multi-temporal glacier area datasets across the HMA are limited due to challenges posed by seasonal snow and cloud cover in remote sensing satellite images. In this study, a new method is proposed to estimate glacier and nonseasonal snow (GNS) areas by combining the normalized difference snow index (NDSI) and bright temperature bands from Landsat remote sensing images in 1990s, 2000s, 2010s and 2020s. Meanwhile, the integrated ice dynamic Open Global Glacier Model (OGGM) is applied to simulate nine typical glaciers and project their changes using 15 general circulation models (GCMs) under four shared socioeconomic pathways (SSPs). The results showed that total GNS areas in HMA were estimated at 71.26 × 103 km2 in the 1990s, and decreased to 53.17 × 103 km2 in the 2020s. Massive proportions of GNS were mainly distributed in the southeast and northwest region. Tipping points of GNS indicating a transition from mass balance gain to loss during four periods were detected in the Upper Tarim basin, Inner Tibetan Plateau, Upper Yangtze river basin, Upper Brahmaputra river basin, and Upper Salween river basin. The reduction of total GNS area was attributed to significantly rising temperature and decreasing solid precipitation. The projections indicate that glacier shrinkages will be the dominant trend in the future, and most typical glaciers will experience a mass loss of 60% under SSP245 (SSP2-RCP4.5) and over 90% under SSP585 (SSP5-RCP8.5) by the end of the century. The response of glaciers to climate change is also found to be influenced by factors including local topography and elevation ranges. The findings of this study provides a better understanding of glacial dynamics in response to climate change and highlights the importance of making water resources management strategies to mitigate the influence of glacier retreat.

Shifted sediment-transport regimes by climate change and amplified hydrological variability in cryosphere-fed rivers

Climate change affects cryosphere-fed rivers and alters seasonal sediment dynamics, affecting cyclical fluvial material supply and year-round water-food-energy provisions to downstream communities. Here, we demonstrate seasonal sediment-transport regime shifts from the 1960s to 2000s in four cryosphere-fed rivers characterized by glacial, nival, pluvial, and mixed regimes, respectively. Spring sees a shift toward pluvial-dominated sediment transport due to less snowmelt and more erosive rainfall. Summer is characterized by intensified glacier meltwater pulses and pluvial events that exceptionally increase sediment fluxes. Our study highlights that the increases in hydroclimatic extremes and cryosphere degradation lead to amplified variability in fluvial fluxes and higher summer sediment peaks, which can threaten downstream river infrastructure safety and ecosystems and worsen glacial/pluvial floods. We further offer a monthly-scale sediment-availability-transport model that can reproduce such regime shifts and thus help facilitate sustainable reservoir operation and river management in wider cryospheric regions under future climate and hydrological change.

Long-term analysis of glaciers and glacier lakes in the Central and Eastern Himalaya

Himalayan glaciers represent both an important source of water and a major suite of geohazards for inhabitants of their downstream regions. Recent climate change has intersected with local topographic, geomorphic, and glaciological factors to drive complex patterns of glacier thinning, retreat, velocity change, and lake development. In this study, we analyze the long-term variations in surface elevation change and velocity of the glaciers in the Central and Eastern Himalaya using existing and newly generated datasets spanning 1975 to 2018. We have used modelled (e.g., debris and ice thickness) and remote sensing datasets (e.g., Corona, Hexagon, and Landsat images) to investigate the impact of debris cover and the evolution of proglacial lakes on the glacier response in the region. We found that lake-terminating glaciers (lake TGs) have significantly higher thinning, velocity, and deceleration over time than land-terminating glaciers (land TGs). Lakes have shown an overall growth of 98 % in area and 40 % in number during 1975-2017. New proglacial lakes will likely continue to develop, and existing ones will keep expanding, influencing the frontal changes and dynamics of the lake-terminating glaciers. Debris-covered glaciers have undergone similar thinning compared to clean-ice glaciers, both for lake and land TGs; however, variations exist across the ablation zones between clean and debris-covered glaciers which this study further explores using a data-driven approach. Overall, the proglacial lakes development, changes in debris coverage, and topography significantly affect the glacier responses in the regions.