Asian Water Tower Research Articles

Spatial–temporal variations in riverine carbon strongly influenced by local hydrological events in an alpine catchment

Abstract. Headwater streams drain >70 % of global land areas but are poorly monitored compared with large rivers. The small size and low water buffering capacity of headwater streams may result in a high sensitivity to local hydrological alterations and different carbon transport patterns from large rivers. Furthermore, alpine headwater streams on the “Asian water tower”, i.e., Qinghai–Tibetan Plateau, are heavily affected by thawing of frozen soils in spring as well as monsoonal precipitation in summer, which may present contrasting spatial–temporal variations in carbon transport compared to tropical and temperate streams and strongly influence the export of carbon locked in seasonally frozen soils. To illustrate the unique hydro-biogeochemistry of riverine carbon in Qinghai–Tibetan headwater streams, here we carry out a benchmark investigation on the riverine carbon transport in the Shaliu River (a small alpine river integrating headwater streams) based on annual flux monitoring, sampling at a high spatial resolution in two different seasons and hydrological event monitoring. We show that riverine carbon fluxes in the Shaliu River were dominated by dissolved inorganic carbon, peaking in the summer due to high discharge brought by the monsoon. Combining seasonal sampling along the river and monitoring of soil–river carbon transfer during spring thaw, we also show that both dissolved and particulate forms of riverine carbon increased downstream in the pre-monsoon season due to increasing contribution of organic matter derived from thawed soils along the river. By comparison, riverine carbon fluctuated in the summer, likely associated with sporadic inputs of organic matter supplied by local precipitation events during the monsoon season. Furthermore, using lignin phenol analysis for both riverine organic matter and soils in the basin, we show that the higher acid-to-aldehyde (Ad/Al) ratios of riverine lignin in the monsoon season reflect a larger contribution of topsoil likely via increased surface runoff compared with the pre-monsoon season when soil leachate lignin Ad/Al ratios were closer to those in the subsoil than topsoil solutions. Overall, these findings highlight the unique patterns and strong links of carbon transport in alpine headwater catchments with local hydrological events. Given the projected climate warming on the Qinghai–Tibetan Plateau, thawing of frozen soils and alterations of precipitation regimes may significantly influence the alpine headwater carbon transport, with critical effects on the biogeochemical cycles of the downstream rivers. The alpine headwater catchments may also be utilized as sentinels for climate-induced changes in the hydrological pathways and/or biogeochemistry of the small basin.

Development and evaluation of spectral nudging strategy for the simulation of summer precipitation over the Tibetan Plateau using WRF (v4.0)

Abstract. Precipitation is the key component determining the water budget and climate change of the Tibetan Plateau (TP) under a warming climate. This high-latitude region is regarded as “the Third Pole” of the Earth and the “Asian Water Tower” and influences the eco-economy of downstream regions. However, the intensity and diurnal cycle of precipitation are inadequately depicted by current reanalysis products and regional climate models (RCMs). Spectral nudging is an effective dynamical downscaling method used to improve precipitation simulations of RCMs by preventing simulated fields from drifting away from large-scale reference fields, but the most effective manner of applying spectral nudging over the TP is unclear. In this paper, the effects of spectral nudging parameters (e.g., nudging variables, strengths, and levels) on summer precipitation simulations and associated meteorological variables were evaluated over the TP. The results show that using a conventional continuous integration method with a single initialization is likely to result in the over-forecasting of precipitation events and the over-forecasting of horizontal wind speeds over the TP. In particular, model simulations show clear improvements in their representations of downscaled precipitation intensity and its diurnal variations, atmospheric temperature, and water vapor when spectral nudging is applied towards the horizontal wind and geopotential height rather than towards the potential temperature and water vapor mixing ratio. This altering of the spectral nudging method not only reduces the wet bias of water vapor in the lower troposphere of the ERA-Interim reanalysis (when it is used as the driving field) but also alleviates the cold bias of atmospheric temperatures in the upper troposphere, while maintaining the accuracy of horizontal wind features for the regional model field. The conclusions of this study imply how driving field errors affect model simulations, and these results may improve the reliability of RCM results used to study the long-term regional climate change.

Tibetan Plateau vortex‐associated precipitation and its link with the Tibetan Plateau heating anomaly

AbstractThe Tibetan Plateau (TP) is known as the Asian water tower that supplies fresh water for millions of people in Asia. The Tibetan Plateau vortices (TPVs) are one of the major precipitation‐producing weather systems over the TP. The characteristics of TPV‐associated precipitation from 1979 to 2017 are quantitatively analysed based on three daily precipitation datasets. The influence of TPVs on precipitation is more significant in the warm season (May–September) because the precipitation and TPV activities both peak in the warm season. The TPV‐associated precipitation (VAP) dominates the total precipitation over most of the TP in the warm season. The VAP contributes more than 50% of the total precipitation in the warm season over 30% of the area over the TP, particularly in the central TP, while the VAP accounts for more than 25% of the total precipitation in the cold season over about 20% of the area over the TP. Therefore, TPVs are the major systems to produce precipitation on the TP in the warm season, and they are also important in the cold season in certain regions. The interannual variation of VAP is mainly determined by the number, rather than the precipitation intensity, of TPVs. Furthermore, the heating anomaly caused by the TP thermodynamic effect is an influential factor of VAP. Stronger (weaker) TP heating and resulting ascending motion strengthen (attenuate) the convergence near the TP surface and the divergence in the upper troposphere. The thermal adaption‐associated circulation generates more (less) TPVs and VAP.

The Mechanism of Increasing Summer Water Vapor Over the Tibetan Plateau

AbstractRapid warming over the Tibetan Plateau (TP) has been associated with an increasing trend in atmospheric water vapor content, which is critical for recharging the Asian water tower. However, the mechanism associated with the wetting phenomenon remains unclear. Long‐term changes in moisture balance and precipitation (PRE) recycling processes are investigated using the ERA5 reanalysis from 1979 to 2019. The increasing trend over TP is mainly due to the summer water vapor trend with significantly increases over the western TP. Based on the moisture balance analysis, it is found that PRE, evaporation, and the convergence of moisture are all increasing over the western TP but decreasing over the eastern TP. Based on the dynamical PRE recycling model, the results suggest that both internal and external cycles contributes to the wetting over TP, with 63.87% and 36.13% contributions respectively. Further analysis found that the atmospheric heating source is also increasing over the western TP, which could shift the moisture transportation from east to west at the southern boundary of TP. The increasing moisture convergence could enhance PRE, and the enhanced latent heating in the mid‐atmosphere can further induced moisture convergence, which forms a positive feedback. However, an opposite situation occurred over the eastern TP. The internal and external cycle of the water cycle can stimulate (suppress) each other through PRE over the western (eastern) TP. This mechanism linked the changes in the PRE recycling and atmospheric circulation, and induced the increasing trend over TP in summer.

Sink or source? Methane and carbon dioxide emissions from cryoconite holes, subglacial sediments, and proglacial river runoff during intensive glacier melting on the Tibetan Plateau

High Mountain Asia glaciers are currently ignored in the estimation of global greenhouse gas budgets (e.g., methane (CH4) and carbon dioxide (CO2)). Similar to the Asian Water Tower and Third Pole, the Tibetan Plateau (TP) hosts the largest volume of glaciers outside the polar regions. These glaciers contain large reservoirs of organic carbon that can influence glacial ecosystems under rapid melting. However, no data exist on the current footprint of CH4 and CO2 from glaciers in the TP. Here, we report in situ observations of CH4 and CO2 fluxes for glacial cryoconite holes, subglacial sediments, and proglacial river runoff across the TP. Our results indicate that cryoconite holes and subglacial sediments can accelerate the export of greenhouse gasses during the melting season due to intensive glacier melting. However, to some extent, proglacial river runoff can be a significant sink of atmospheric CO2; this fact was not identified in previous studies. Our findings suggest that variations (source or sink) of greenhouse gasses from TP glacial basins should be considered in regional CH4 and CO2 budgets under climate warming.

Accelerating permafrost collapse on the eastern Tibetan Plateau

Permafrost collapse can rapidly change regional soil-thermal and hydrological conditions, potentially stimulating production of climate-warming gases. Here, we report on rate and extent of permafrost collapse on the extensive Tibetan Plateau, also known as the Asian Water Tower and the Third Pole. Combined data from in situ measurements, unmanned aerial vehicles (UAV), manned aerial photographs, and satellite images suggest that permafrost collapse was accelerating across the Eastern Tibetan Plateau. From 1969 to 2017, the area of collapsed permafrost has increased by approximately a factor of 40, with 70% of the collapsed area forming since 2004. These widespread perturbations to the Tibetan Plateau permafrost could trigger changes in local ecosystem state and amplify large-scale permafrost climate feedbacks.

Anthropogenic warming of Tibetan Plateau and constrained future projection

Serving as ‘the water tower of Asia’, the Tibetan Plateau (TP) supplies water resources to more than 1.4 billion people. It is warming more rapidly than the global average over the past decades, affecting regional hydrological cycle and ecosystem services. However, the anthropogenic (ANT) influence remains unknown. Here we assessed the human contribution to the observed TP warming based on coupled climate simulations and an optimal fingerprinting detection and attribution analysis. We show that the observed rapid warming on the TP (1.23 °C over 1961–2005) is attributable to human influence, and particularly, to the greenhouse gases with a contribution of 1.37 °C by the best estimate, which was slightly offset by anthropogenic aerosols. As the multi-model ensemble tends to underestimate the ANT warming trend, the constraint from the attribution results suggests an even warmer future on the TP than previously expected, implying further increased geohazard risks in the Asian water tower.

Tibetan Plateau Precipitation Modulated by the Periodically Coupled Westerlies and Asian Monsoon

AbstractKnowledge of decadal‐centennial‐scale precipitation cycles is important for predicting the status of water resources and thus food security in the region influenced by the “Asian Water Tower” (the Tibetan Plateau, TP). However, the drivers of these precipitation cycles in the TP remain unclear. Here we present a 1,656‐years (5‐years‐resolution) mean annual precipitation record reconstructed by fossil pollen assemblages from the annually laminated sediments of a lake in the TP interior. The record reveals three dominant cycles, with lengths of ∼200‐, ∼88‐, and ∼60‐years, associated with changes in the Westerlies and the Asian monsoon. These precipitation cycles suggest that the current high precipitation in the TP interior results from the superposition of cyclic highs in precipitation, and this trend may continue for the next several decades.

Spatio-temporal dynamics of hydrologic changes in the Himalayan river basins of Nepal using high-resolution hydrological-hydrodynamic modeling

The hydrology of the Himalayan region, known as the water tower of Asia, is undergoing rapid transformations due to climate change and growing human influences, and it is known that this region is one of those most vulnerable to climate change. Numerous studies have examined the changes in the hydrology of Nepal, which includes a significant upstream portion of the Himalayas. However, there is a lack of holistic studies on the spatial–temporal evolution of hydrologic dynamics over the entire nation and over long periods. In this study, we present a comprehensive assessment of the changes in river discharge, flood occurrence, and terrestrial water storage (TWS) across all river basins in Nepal using hydrological-hydrodynamic simulations spanning for 40 years (1979–2018) at ~ 5 km spatial resolution, and downscaled flood attributes at ~ 90 m resolution. The spatio-temporal variations in river discharge and inundation extent are examined through mapping of decadal trends using a quantile analysis method. The results indicate that the dynamics of river discharge has evolved varyingly across different river basins. The evolution pattern within a basin generally agrees with that at the basin outlet, but notable exceptions are found, indicating high hydro-climatic heterogeneity within the basins. The decadal evaluation of flood dynamics over major flooded areas suggests that inundation dynamics is strongly influenced by various flow characteristics, including the timing, duration, and magnitude, and that the evolution of flood dynamics is more complex than that of river discharge. Results indicate that the TWS dynamics over entire Nepal is strongly modulated by the variations in subsurface water storage, and groundwater storage has been in continuous decline (-1.74 cm/year) in the recent decades (2002–2016). This study provides a basis to advance the understanding of long-term hydrologic changes in the Himalayan region with important implications for improved water resources management.

Regional assessment of the potential risks of rapid lake expansion impacting on the Tibetan human living environment

High-altitude inland lakes on the Tibetan Plateau (TP) play a crucial role in maintaining the water balance of Asian water towers and are the key indicators of climate change and variability. Over the past several decades, dramatic lake expansions in the endorheric Tibetan basins have exerted pronounced influences on the environmental changes of the unique highland. However, the potential influences of rapid lake growth on human living environment were rarely reported. The objective of this study is to analyze the influence or potential risk of rapid lake expansion on the living environment (including settlements and transportation facility) of the TP by referring to the recent lake growth rate since the early 21st century. This study examines the change characteristics of 139 Tibetan terminal lakes larger than 1 km2 from 2000 to 2018, and shows that the area and water storage of these examined lakes increased by 2,737.40 km2 and 89.37 km3, respectively, from 2000 to 2018. Furthermore, we assessed the submerging risk levels and potential influences of the rapid lake expansions on the local living environment by disentangling different lake drainage basins and administrative units, focusing on residential areas and road networks. The results indicate that 393 residential settlements and 393.90 km of road segments will be probably submerged within the next 20 years. The predicted high-risk townships might mainly concentrate in the southern and central parts of the Nagqu Prefecture, including Rongma, Qiangma, and Beila Townships. The study provides essential scientific references for evaluating the potential threats of lake growth on local people in Tibet and taking risk mitigation actions under the context of climate change.

Distributed hydrological model of the Qinghai Tibet Plateau based on the hydrothermal coupling: I: hydrothermal coupling simulation of "snow-soil-sand gravel layer" continuum

The Qinghai-Tibet Plateau, known as the Asian Water Tower, is a typical alpine mountain area. Snow-covered permafrost and seasonally frozen soil widely exist on this plateau, profoundly affecting the water cycle process of the entire region. In addition, the Qinghai-Tibet Plateau has the characteristics of a thinner soil and a thicker underlying sand and gravel layer, forming a special snow-soil-sand gravel layer hydrothermal medium structure. To further study the water cycle mechanism of the Qinghai-Tibet Plateau, this study selected the Niyang River basin as a typical area to perform field-heat-coupling experiments in the field. Combined with the geological and climatic characteristics of the Qinghai-Tibet Plateau, a 12-layer snow-soil-sand gravel layer continuum was constructed to describe the hydro-thermal coupling model of the Qinghai-Tibet Plateau. A complete hydro-thermal coupling simulation equation and parameter calculation method are described. The model was validated using the measured results of the temperature, liquid water content, and freezing depth of the soil and gravel in the freezing and thawing period of 0-160 cm from 2016 to 2017. The mean values of the simulated R2 of the temperature of each and the moisture content during freezing and thawing were 0.91 and 0.52, respectively. The R2 of the soil freezing depth is 0.76. The results show that the model can better reflect the hydrothermal variation of stratified soil and sand gravel during freezing and thawing processes. The results show that the model has adequate applicability in the Qinghai-Tibet Plateau and can reflect the special change process of moisture and temperature of the soil and gravel during the freezing and melting processes in this area.

Sedimentation rate variations of the proglacial lake (Qiangyong Co) and its implications for glacial fluctuations over the past century, southern Tibet, China<sup>*</sup>

青藏高原上分布着大量的大陆性冰川，其对区域及全球气候变化响应极其敏感.工业革命以来，随着全球升温速率加快（特别是北半球），青藏高原部分地区的冰川在近百年显著退缩.冰前湖沉积物是最直接的冰川变化记录载体之一，但其沉积速率如何响应冰川及气候变化，能否反演冰川进退过程却知之甚少.本文依据²¹⁰Pb和¹³⁷Cs限定藏南冰前湖枪勇错QY5沉积岩芯的年龄，计算出不同深度沉积物的沉积速率，且与前人（QY-3）的沉积速率进行对比，揭示了近百年来枪勇错流域冰川变化历史及其与气温之间的关系.结果表明，枪勇错QY5近百年来的平均沉积速率为0.21 cm/a，比湖心（QY-3）快2倍左右，但两者的变化基本同步，高沉积速率对应温度上升期，是冰川退缩的直接响应：（1）1900-1960年，枪勇错沉积速率整体增加且变幅较大，与1890-1950年之间西藏温度波动式升高相对应，反映枪勇冰川总体处于退缩状态；（2）1960-1985年，沉积速率低且变幅较小，同期气温下降，枪勇冰川退缩程度相对较低且保持平稳；（3）1985年以来，枪勇错沉积速率呈上升趋势，是全球增暖下冰川显著退缩的直接响应.在短时间尺度内冰前湖沉积速率所揭示的枪勇冰川变化主要受控于温度，降水量对冰川变化的影响较小，但冰川对温度变化的响应滞后5~10 a.由于全球变暖和冰川对温度响应的滞后，在未来几十年高原冰川的融化速率可能会加快，亚洲水塔将面临着新的挑战.;Continental glaciers on the Tibetan Plateau are sensitive to regional and global climate change. Since the industrial revolution, with the acceleration of global warming (especially in the Northern Hemisphere), glaciers in most parts of the Tibetan Plateau have shrunk significantly over the past century. The sediments in proglacial lakes are one of the direct record carriers of glacial fluctuations, but little is known about how their sedimentation rate (SR) responds to glacier and climate changes, particularly under the background of global warming. In this study, the ²¹⁰Pb and ¹³⁷Cs activities were used to constrain the age of a core (QY5) from Qiangyong Co in southern Tibet and to calculate the SRs of the core sediments at different depths. By comparing the SRs of the core (QY5) with those of the QY-3 core from central Qiangyong Co, the history of glacial fluctuations and its relationship with air temperature during the last century were revealed. The results show that the average SR of upstream of Qiangyong Co (QY5) is 0.21 cm/a, about double of the centre of the lake (QY-3), but with the same patterns. High SRs are corresponded to warm temperatures, as a direct response to the glacial retreat within the Qiangyong catchment: (1) from 1900s to 1960s, the SR of Qiangyong Co increased and fluctuated greatly as a result of the glacial retreat, corresponding to increased temperature in Tibet between 1890s and 1950s; (2) during 1960s-1985 when temperature decreased, the SR was low and stable, indicating stable Qiangyong glacier; (3) since 1985, the SR in Qiangyong Co increased gradually, as a direct response to glacier retreat under the acceleration of the global warming. Over a short time scale, the change of the Qiangyong glacier revealed by the SR in the proglacial lake is mainly controlled by air temperature, rather than by precipitation. However, there is a 5 to 10 years delay of glacier retreat to increased temperature. Due to global warming and the delayed response of glacier retreat to temperature, the melting rate of the Qiangyong glacier may accelerate in the next decades, and the Asian water tower will face a new challenge.

Simulation analysis of local land atmosphere coupling in rainy season over a typical underlying surface in the Tibetan Plateau

Abstract. The local land–atmosphere coupling (LoCo) investigates the interactions between soil conditions, surface fluxes, planetary boundary layer (PBL) growth, and the formations of convective clouds and precipitation. Studying LoCo over the Tibetan Plateau (TP) is of great significance for understanding the TP's role in the Asian water tower. A series of real-case simulations, using the Weather Research and Forecasting (WRF) model with different combinations of land surface model (LSM) schemes and PBL schemes, has been carried out to investigate the LoCo characteristics over a typical underlying surface in the central TP in the rainy season. The LoCo characteristics in the study area are analyzed by applying a mixing diagram to the simulation results. The analysis indicates that the WRF simulations, using the Noah with BouLac, Mellor-Yamada Nakanishi and Niino Level-2.5 PBL (MYNN), and Yonsei University (YSU) produce closer results to the observation in terms of curves of Cp⋅θ and Lv⋅q, surface fluxes (Hsfc and LEsfc), entrainment fluxes (Hent, and LEent) at site BJ of Nagqu Station (BJ/Nagqu) than those using the Community Land Model (CLM) with BouLac, MYNN, and YSU. The frequency distributions of Hsfc, LEsfc, Hent, and LEent in the study area confirm this result. The spatial distributions of simulated Hsfc, LEsfc, Hent, and LEent, using WRF with Noah and BouLac, suggest that the spatial distributions of Hsfc and LEsfc in the study area are consistent with that of soil moisture, but the spatial distributions of Hent and LEent are quite different from that of soil moisture. A close examination of the relationship between entrainment fluxes and cloud water content (QCloud) reveals that the grids with small Hent and large LEent tend to have high QCloud and Hsfc, suggesting that high Hsfc is conducive to convective cloud formation, which leads to small Hent and large LEent. A sensitivity analysis of LoCo to the soil moisture at site BJ/Nagqu indicates that, on a sunny day, an increase in soil moisture leads to an increase in LEsfc but decreases in Hsfc, Hent, and LEent. The sensitivity of the relationship between simulated maximum daytime PBL height (PBLH) and mean daytime evapotranspiration (ET) in the study area to soil moisture indicates the rate at which the maximum daytime PBLH decreases with the mean ET increase as the initial soil moisture goes up. The analysis of simulated Hsfc, LEsfc, Hent, and LEent under different soil moisture conditions reveals that the frequency of Hent ranging from 80 to 240 W m−2 and the frequency of LEent ranging from −240 to −90 W m−2 both increase as the initial soil moisture increases. Coupled with the changes in QCloud, the changes in Hent and LEent as the initial soil moisture increases indicate that the rise in soil moisture leads to an increase in the cloud amount but a decrease in QCloud.

Regional differences of water regulation services of terrestrial ecosystem in the Tibetan Plateau: Insights from multiple land covers

As a critical service of terrestrial ecosystem, water regulation (conservation and provision) shows complicated regional heterogeneities due to interactions of various land covers and climate conditions. The widely used valuation methods usually lack accurate descriptions of hydrological responses to multiple land covers, and also ignore their regional differences at large scales. Tibetan Plateau is well known as the Asian water tower with the most diverse and vulnerable ecosystems, and 44 counties in the Brahmaputra, Salween and Lancang River Basins, and Qinghai Region are selected as our study area. The terrestrial ecosystem services are valuated for individual land covers at county scale using improved hydrological simulations for alpine regions (particularly freezing and thawing process simulations of snow cover and glacier), and their regional differences are further identified using multivariate statistical analysis. Results show that runoff hydrographs at most stations are well reproduced with relative bias within ±15%, and average correlation coefficient and efficiency coefficient of 0.88 and 0.72, respectively. The total water regulation values are from US$ 0.59 × 108 to US$ 69.80 × 108 at county scale, accounting for 4.6%–7807.7% of local gross domestic products in the 2015 price level. Thereinto, the water conservation values are the greatest for grass (15.2%–91.2% of total), followed by forest (0.0%–51.3%) and cropland (0.0%–32.4%), while the water provision values are the greatest for glacier (0.0%–80.9%), followed by waterbody (0.0%–38.2%). The water conservation zones of grass, forest and cropland, and the water provision zones of glacier and waterbody are identified, and show obvious regional differences. These zones are in 61.4% of total counties, middle and downstream counties (20.5%), downstream counties of Qinghai Region (4.5%), source counties (9.1%), and middle stream counties of Qinghai Region (4.5%), respectively. This study gives new insights into the valuation of terrestrial ecosystem services in alpine regions, and provides scientific evidence for regional ecological compensations and protection in the Tibetan Plateau.

Microplastics in glaciers of the Tibetan Plateau: Evidence for the long-range transport of microplastics

Microplastics are globally prevalent on a large scale in various marine and terrestrial environments, including Arctic snow and precipitation in protected areas of the United Sates. However, reports of microplastics from glaciers are rare, especially for the Tibetan Plateau (TP), which is widely known as the world's Third Pole and Asian Water Tower. Adjacent to human settlements in South Asia, East China, and Central Asia, the TP features regular cross-border air pollution (e.g., black carbon and mercury), which can affect its vulnerable and pristine environments. In previous studies, abundant microplastics have been reported from Tibetan rivers/lakes water and sediments, and surface soils. We detected microplastics in glacier surface snow on the TP, which were isolated from the impact of human activities, indicating that microplastics can be transported over long distances. This evidence is expected to be significant for understanding the atmospheric transport of microplastics to the TP, and provides a global perspective on the microplastic cycle.

Spatial and seasonal variations of dissolved arsenic in the Yarlung Tsangpo River, southern Tibetan Plateau

High levels of dissolved arsenic (As) have been reported in many rivers running though the Tibetan Plateau (TP), the “Water Tower of Asia”. However, the source, spatiotemporal variations, and geochemical behavior of dissolved As in these rivers remain poorly understood. In this study, hot spring, river water, and suspended particulate material samples collected from the Yarlung Tsangpo River (YTR) (upper reaches of the Brahmaputra River) system in 2017 and 2018 were analyzed. Spatial results shown that the upper reaches of YTR (Zone I) have comparatively high levels of dissolved As ([As]dissolved: mean 31.7 μg/L; 4.7–81.6 μg/L; n = 16), while the tributaries of the lower reaches (Zone II) have relatively low levels (mean 0.54 μg/L; 0.11–1.3 μg/L; n = 7). Seasonal results shown that the high [As]dissolved (6.1–22.4 μg/L) were found in September to June and low [As]dissolved (1.4–3.7 μg/L) were observed in July to August. Geothermal water is suspected as the main source of the elevated As levels in YTR due to the extremely high [As]dissolved in hot springs (1.13–9.76 mg/L) and abundance of geothermal systems throughout TP. However, the seasonal results suggested that weathering of As-containing rocks and minerals is also a key factor affecting the [As]dissolved in the river water in July to August (wet-season). Natural attenuation of As in main channel is dominated by dilution process due to the lower As concentrations in tributaries, but mostly occurred by both dilution and adsorption (or co-precipitation) processes in tributaries. This work highlights that the weathering process may have an important contribution to the dissolved As in the river waters in wet-season, and the geochemical behavior of As is largely transported conservatively in the main channel and relative non-conservatively in the tributaries in YTR system.

Emerging water pollution in the world's least disturbed lakes on Qinghai-Tibetan Plateau.

Qinghai-Tibet Plateau (QTP) Lake Region has largest abundance and size distribution of lakes in China. Being relatively away from major human activities, the water quality of these lakes has not attracted concerns in the past. However, dramatic climate change and intensified anthropogenic activities over the past 30 years have exerted multiple pressures on the water environment of the lakes, resulting in elevated nutrient concentrations in major freshwater lakes of the region. Rapid water quality deterioration and eutrophication of the lakes were first found in Lake Hurleg in the northeast of the plateau. Analyses of driving forces associated with these changes indicate that both the intrinsic characteristics of the QTP lakes and climate change were responsible for the vulnerability to human activities than other lakes in different regions of China, with accelerated urbanization and extensive economic development in the lake basin playing a decisive role in creating water pollution events. Under combination pressures from both natural and anthropogenic effect, the increasing rate of nutrient concentrations in Lake Hurleg has been 53-346 times faster than in Lake Taihu and Lake Dianchi during the deterioration stage. The result suggests the current development mode of Lake Hurleg basin is not suitable for setting protection targets for the QTP lake region more broadly due to its extremely poor environmental carrying capacity. To stop worsening the lake water environment condition, it is necessary to review the achievements made and lessons learned from China's fight against lake pollution and take immediate measures, inform policies into the development mode in the QTP lake region, and avoid irreversible consequences and ensure good water quality in the "Asian Water Tower."

Water clarity changes in 64 large alpine lakes on the Tibetan Plateau and the potential responses to lake expansion

Lakes are essential components of the water cycle and ecosystems. Therefore, the ecology and water security of lakes is of great concern. However, on the Tibetan Plateau (TP), which is known as the Asian water tower, knowledge of lake water quality is in its infancy. In this study, we developed a Moderate Resolution Imaging Spectroradiometer (MODIS)-based Secchi disk depth (Zsd) retrieval model and used the proposed model to study the temporal and spatial dynamics of water clarity in 64 lakes (>50 km2) located on the TP during the 2003–2018 period. The results show that the 64 lakes have an average long-term mean Zsd of 4.4 ± 3.0 m, where lakes in the northern TP generally exhibited lower Zsd levels than those located in the southern and northeastern parts of the TP. Among all selected lakes, the number of lakes showing (significantly) decreasing Zsd change trends was approximate to those showing (significantly) increasing change trends. Nevertheless, the two trends exhibited different spatial patterns. An analysis of the potential links between lake Zsd and environmental factors suggests that lake expansion is an essential factor affecting the increase in lake Zsd, while such an impact may be offset by the increase in phytoplankton induced by climate change in lakes showing a significant Zsd decreasing trend. In addition, land use types are partially responsible for the Zsd disparities between different lakes since lakes with high Zsd commonly occurred with high vegetation cover in their surrounding areas, while glacial melting and hydrological networks showed minor influences. This study is expected to enhance our understanding of lacustrine environments in TP and other global alpine lakes under the scenario of climate change.

Six Decades of Glacier Mass Changes around Mt. Everest Are Revealed by Historical and Contemporary Images

Summary The accurate quantification of current and past Himalayan glacier mass budgets is vital if we are to understand the evolution of the Asian water tower, which provides water to the planet’s most populous region. In this work, we generated a geodetic time series spanning six decades over 79 glaciers surrounding Mt. Everest and found consistent acceleration of glacier mass loss between the 1960s (−0.23 ± 0.12 mwe a−1) and the modern era (−0.38 ± 0.11 mwe a−1 from 2009 to 2018). Glacier mass loss has varied depending on glacier terminus type and surface characteristics, and glacier thinning is now occurring at extreme altitudes (>6,000 masl). Our time series also captures the first documented surge of a glacier in the Mt. Everest region. These multi-decadal observations of glacier mass loss form a baseline dataset against which physically based glacier evolution models could be calibrated before they are used for predicting future meltwater yield.

La hidropolítica y las relaciones exteriores de China en el complejo hídrico del Himalaya; los casos de Nepal e India

Los diez sistemas de ríos principales del continente asiático nacen en el Himalaya, la gran mayoría, en la enorme meseta tibetana. China es uno de los países con más ríos transfronterizos en el mundo, solo superado por Rusia y Argentina. La torre de agua de Asia se encuentra en una posición que le confiere un enorme poder e influencia, y las decisiones que adopte en el campo de sus relaciones hidráulicas con el resto de países tiene un alcance regional, continental y, posiblemente, global. La gestión de sus 16 ríos transfronterizos puede afectar la disponibilidad de agua de muchos países río abajo, con afectación directa al acceso a los recursos hídricos de 14 países en el continente asiático y de casi tres billones de personas, es decir casi la mitad de la población mundial El objetivo del presente artículo es analizar el comportamiento hidráulico chino en el complejo del Himalaya, a partir de dos casos de estudio: las relaciones de China con Nepal e India. Se pretende así contribuir al debate sobre, por una parte, los factores explicativos del comportamiento hídrico de la potencia asiática, prestando especial atención a la importancia de la meseta tibetana y, por el otro, al debate académico sobre la estrategia china en relación con uno de los recursos más apreciados del planeta, el agua. China cuenta hoy en día con unas 90.000 infraestructuras hidráulicas, contando presas, diques y proyectos de desvío de agua, y sus intereses hídricos abarcan tanto ríos internos —que acusan la escasez y la sequía con más gravedad, como el Amarillo o el Yangtzé— como los ríos transfronterizos internacionales, lo que conlleva de inmediato una amenaza para los países con los que comparte estos ríos —como el Brahmaputra. El principal argumento es que la política china en el Himalaya es un eslabón más en el intento chino de consolidar su presencia política y estratégica en diferentes partes del mundo. Las relaciones hídricas chinas se deben analizar en el contexto de la política exterior del gigante asiático en la última década, marcada por su expansionismo, su cristalización como gran potencia mundial, y su estilo de política exterior a escala global El artículo se estructura de la siguiente forma. El primer apartado contiene el marco teórico y analítico del articulado, empezando por el paraguas conceptual que nos ofrece la hidropolítica para entender el comportamiento en términos hídricos de China en el espacio del Himalaya, en base a dos conceptos principales: hidrohegemonía e hidrodominación. El segundo apartado contiene una disección analítica del Himalaya como complejo hídrico y el estudio de los casos relevantes para entender el comportamiento de China en el sistema himalayo; Nepal e India. El análisis de los factores explicativos de la política hídrica china, a nivel endógeno y exógeno, así como la estrategia seguida por Pekín, sustentan el tercer apartado del documento. Las conclusiones y consideraciones finales cierran el presente artículo.