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The Tibetan Plateau (TP) has warmed at a rate twice the global average and presents unique warming patterns in surface temperature changes. However, key characteristics of glacier surface heatwave duration and intensity over the TP during the present extreme warming period are still unknown. In this study, we show that surface temperatures in glacial regions of the TP (0.37 ± 0.10°C per decade) have increased faster than those in non‐glacial areas (0.29 ± 0.05°C per decade) between 2001 and 2020. Moreover, the duration (5.3 ± 3.2 days per decade) and cumulative intensity (24.9 ± 16.3 days °C per decade) of glacier surface heatwaves have increased significantly during autumn. Our results demonstrate an elevation dependence to these key warming characteristics, which we also suggest are associated with extreme glacier mass loss. Here, we highlight potential threats to the sustainability of glacier water resources and increasing risk of glacier related hazards at the "roof of the world." Plain Language Summary: The Tibetan Plateau, commonly referred to as "the roof of the world," has experienced substantial warming during the past 50 years, at a rate twice that of the global average. Previous studies in this climate sensitive environment have primarily focused on air temperature changes measured from a limited number of ground‐based observational stations, as well as from a number of satellite‐derived land surface temperature products. However, the spatiotemporal characteristics of glacier surface heatwaves—periods of extreme warm land surface temperatures—are yet to be explored. In this study, using satellite‐derived land surface temperature data, we investigated temperature changes across the Tibetan Plateau, and critically explored the occurrence of thermal extreme events of glacier surface temperatures from 2001 to 2020. We show that glacial regions have experienced faster surface warming than non‐glacial regions since 2001. Our results also suggest higher surface temperature trends and increases in heatwave intensity and duration during autumn, along with a clear elevation dependence, which is likely due to decreased albedo. Glaciers with extreme high mass loss were highly associated with increases in glacier heatwave duration and intensity. We highlight the implications of glacier heatwave threats to water resources and hazard risk. Key Points: Glacial areas experienced two times higher mean warming rates than non‐glacial areas in autumnThe duration and cumulative intensity of glacier surface heatwaves increased significantly during autumn, likely due to decreased albedoIncreases in glacier surface heatwave duration and cumulative intensity are associated with extreme high glacier mass loss [ABSTRACT FROM AUTHOR]

Understanding the spatial–temporal changes in glacier mass balance and associated drivers on the Tibetan Plateau (TP) is important for predicting future water supplies and glacier-related hazards. However, the comparative study of changes in glacier mass balance in different regions of the same glacierized massif on the TP remains scarce. Combining the reconstructed detailed mass balance time-series from 1970 to 2015 for Ningchan No.1 Glacier in the eastern Qilian Mountains and Qiyi Glacier in the western Qilian Mountains using the energy and mass balance model in this work with the published mass balance data from different glaciers, we find that interannual changes in glacier mass balance are broadly similar in different regions of the Qilian Mountains. These interannual changes are primarily driven by variations in ablation-season (June–September) air temperature (Ta), which impact albedo and melt by changing snowfall and incoming longwave radiation (Lin). We link such interannual mass balance variability to the combination of changes in atmospheric circulation over Europe and changes in sea surface temperature (SST) in the Northwest Pacific during the ablation season which can cause the changes in Ta across the Qilian Mountains. In addition, we find a trend of increasingly negative glacier mass balance across the Qilian Mountains from 1970–1994 compared to 1995–2015. This interdecadal trend is driven by higher ablation-season Ta through increasing Lin and through increasing precipitation falling as rain. Lastly, higher glacier mass loss in the east than in the west Qilian Mountains from 1970–1994 and 1995–2015 was mainly caused by lower glacier area-altitude distribution, as well as a reduction in ablation-season precipitation in the eastern Qilian Mountains. [ABSTRACT FROM AUTHOR]

Precipitation is one of the most important atmospheric inputs to hydrological models. However, existing precipitation datasets for the Third Pole (TP) basins show large discrepancies in precipitation magnitudes and spatiotemporal patterns, which poses a great challenge to hydrological simulations in the TP basins. In this study, a gridded (10 km × 10 km) daily precipitation dataset is constructed through a random-forest-based machine learning algorithm (RF algorithm) correction of the ERA5 precipitation estimates based on 940 gauges in 11 upper basins of TP for 1951–2020. The dataset is evaluated by gauge observations at point scale and is inversely evaluated by the Variable Infiltration Capacity (VIC) hydrological model linked with a glacier melt algorithm (VIC-Glacier). The corrected ERA5 (ERA5_cor) agrees well with gauge observations after eliminating the severe overestimation in the original ERA5 precipitation. The corrections greatly reduce the original ERA5 precipitation estimates by 10%–50% in 11 basins of the TP and present more details on precipitation spatial variability. The inverse hydrological model evaluation demonstrates the accuracy and rationality, and we provide an updated estimate of runoff components contribution to total runoff in seven upper basins in the TP based on the VIC-Glacier model simulations with the ERA5_cor precipitation. This study provides good precipitation estimates with high spatiotemporal resolution for 11 upper basins in the TP, which are expected to facilitate the hydrological modeling and prediction studies in this high mountainous region. Significance Statement: The Third Pole (TP) is the source of water to the people living in the areas downstream. Precipitation is the key driver of the terrestrial hydrological cycle and the most important atmospheric input to land surface hydrological models. However, none of the current precipitation data are equally good for all the TP basins because of high variabilities in their magnitudes and spatiotemporal patterns, posing a great challenge to the hydrological simulation. Therefore, in this study, a gridded daily precipitation dataset (10 km × 10 km) is reconstructed through a random-forest-based machine learning algorithm correction of ERA5 precipitation estimates based on 940 gauges in 11 TP basins for 1951–2020. The data eliminate the severe overestimation of original ERA5 precipitation estimates and present more reasonable spatial variability, and also exhibit a high potential for hydrological application in the TP basins. This study provides long-term precipitation data for climate and hydrological studies and a reference for deriving precipitation in high mountainous regions with complex terrain and limited observations. [ABSTRACT FROM AUTHOR]

In the context of global warming, glaciers in the Asian High Mountains (AHMs) are shrinking at an accelerating rate. Projecting their future change is helpful for understanding the hydrological and climatic effects related to glacier retreat. Here, we projected glacier change in the AHMs from 1979 to 2100 under shared socioeconomic pathway (SSP) scenarios from the perspective of temperature, equilibrium-line altitude (ELA), and accumulation area. The annual mean temperature in the AHMs increased by 1.26°C from 1979 to 2014, corresponding to an increase of 210 m in the mean ELA and a decrease of 1.7×104 km2 in the glacier accumulation area. Under the SSP2-4.5 (SSP5-8.5) scenario, the annual mean temperature in the AHMs would increase by 2.84°C (3.38°C) in 2040–2060 relative to that in 1850–1900, leading to the mean ELA reaching an elevation of 5661 m (5777 m). The accumulation area in the AHMs decreased by 46.3% from 1995 to 2014 and was projected to decrease by 60.1% in 2040–2060. Moreover, the annual mean temperature in the AHMs was projected to increase by 3.76°C (6.44°C) in 2080–2100 relative to that in 1850–1900, corresponding to the ELA reaching an elevation of 5821 m (6245 m) and the accumulation area decreasing to 1.8×104 km2 (0.5×104 km2). These data suggest that the conditions for glacier development will disappear in most of the AHMs, except for extreme high-altitude regions in the Tianshan, Pamir, and Himalaya Mountains. Under the SSP2-4.5 (SSP5-8.5) scenario, when the global mean temperature increases 1.5°C (2°C) above pre-industrial levels, the annual mean temperature will increase by 2.12°C (2.86°C) and the accumulation area will decrease by 15% (48%) in the AHMs compared with that in 1995–2015. Therefore, a 1.5°C increase in global warming would keep 40% more of the glacial accumulation area (1.5×104 km2) in the AHMs compared to a 2°C increase in global warming. [ABSTRACT FROM AUTHOR]

Glacier surface temperature is not only an important indicator of climate change, but is also directly related to glacier physical processes and mass balance. Glaciers over the Third Pole have shown heterogeneous but accelerated mass loss over the past two decades. However, few studies have focused on changes of glacier surface temperature in this region. In this study, we investigate this change from 2000 to 2021 using an altitudinal area-weighting method based on Landsat surface temperature products. The results show that this method can robustly derive inter-annual variability and long-term trends of subregional glacier surface temperature. Over the entire Third Pole, glacier surfaces exhibited warming at the rate of +0.17 ± 0.35 °C dec−1 (p = 0.32). The warming had a distinct seasonal pattern: warming in autumn (+0.50 ± 0.53 °C dec−1, p = 0.06) but cooling in spring (−0.22 ± 0.36 °C dec−1, p = 0.23). Correspondingly, the ablation season 0 °C isotherm altitude has risen >100 m and the glacier area with GST ≥0 °C has expanded by 10%. Moreover, the GST changes displayed large spatial heterogeneity. In the westerlies-dominated regions (e.g., Karakoram and Kun Lun), glacier surfaces showed slight warming or even cooling on average (from −0.10 to +0.06 °C dec−1), while in the monsoon-dominated regions (e.g., East Himalaya, Southeast Tibetan Plateau and Hengduan Mountains), strong warming was observed (> +0.50 °C dec−1, p < 0.05). Glacier surfaces generally showed a faster warming at north slopes than south slopes, especially in the ablation season. These results emphasize that different magnitudes of glacier surface warming are important indicators for the contrasting glacier changes over the Third Pole. The method presented here opens the way to investigate long-term surface temperature change of global mountain glaciers, which can help us further understand the mechanisms of glacier response to global climate change. • Landsat data can accurately estimate the change in glacier surface temperature. • Glacier surfaces are generally warming across the Third Pole but with heterogeneity. • Glacier ablation areas have expanded to high elevations. [ABSTRACT FROM AUTHOR]

Quantifying the climatic effect on residential electricity consumption (REC) can provide valuable insights for improving climate–energy damage functions. Our study quantifies the effect of climate on the REC in Tibet using machine learning algorithm models and model-agnostic interpretation tools of feature importance scores and partial dependence plots. Results show that the climate contributes about 16.46% to total Tibet REC while socioeconomic factors contribute about 83.55%. Precipitation (particularly snowfall) boosts electricity consumption during the cold season. The effect of the climate is stronger in urban Tibet (~25.06%) than rural Tibet (~14.79%), particularly in September when electricity-aided heating is considered optional, as higher incomes amplified the REC response to the climate. With urbanization and income growth, the climate is expected to contribute more to Tibet REC. Hence, precipitation should be incorporated in climate–REC functions for the social cost of carbon (SCC) estimation, particularly for regions vulnerable to snowfall and blizzards. Herein, we developed a model-agnostic method that can quantify the total effect of the climate while differentiating between contributions from temperature and precipitation, which can be used to facilitate interdisciplinary and cross-section analysis in earth system science. Moreover, this data-driven model can be adapted to warn against extreme weather induced power outages. [ABSTRACT FROM AUTHOR]

Meltwater from the cryosphere contributes a significant fraction of the freshwater resources in the countries receiving water from the Third Pole. Within the ESA-MOST Dragon 4 project, we addressed in particular changes of glaciers and proglacial lakes and their interaction. In addition, we investigated rock glaciers in permafrost environments. Here, we focus on the detailed investigations which have been performed in the Poiqu River Basin, central Himalaya. We used in particular multi-temporal stereo satellite imagery, including high-resolution 1960/70s Corona and Hexagon spy images and contemporary Pleiades data. Sentinel-2 data was applied to assess the glacier flow. The results reveal that glacier mass loss continuously increased with a mass budget of −0.42 ± 0.11 m w.e.a−1 for the period 2004–2018. The mass loss has been primarily driven by an increase in summer temperature and is further accelerated by proglacial lakes, which have become abundant. The glacial lake area more than doubled between 1964 and 2017. The termini of glaciers that flow into lakes moved on average twice as fast as glaciers terminating on land, indicating that dynamical thinning plays an important role. Rock glaciers are abundant, covering approximately 21 km2, which was more than 10% of the glacier area (approximately 190 km2) in 2015. With ongoing glacier wastage, rock glaciers can become an increasingly important water resource. [ABSTRACT FROM AUTHOR]

Accurate estimates of regional ice thickness, which are generally produced by ice-thickness inversion models, are crucial for assessments of available freshwater resources and sea level rise. A digital elevation model (DEM) derived from surface topography of glaciers is a primary data source for such models. However, the scarce in situ measurements of glacier surface elevation limit the evaluation of DEM uncertainty. Hence the influence of DEM uncertainty on ice-thickness modeling remains unclear over the glacierized area of the Tibetan Plateau (TP). Here, we examine the performance of six widely used and mainly global-scale DEMs: AW3D30 (ALOS – Advanced Land Observing Satellite – World 3D – 30 m; 30 m), SRTM-GL1 (Shuttle Radar Topography Mission Global 1 arc second; 30 m), NASADEM (NASA Digital Elevation Model; 30 m), TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement, synthetic-aperture radar; 90 m), SRTM v4.1 (Shuttle Radar Topography Mission; 90 m), and MERIT (Multi-Error-Removed Improved-Terrain; 90 m) over the glacierized TP by comparison with ICESat-2 (Ice, Cloud and land Elevation Satellite) laser altimetry data while considering the effects of glacier dynamics, terrain factors, and DEM misregistration. The results reveal NASADEM to be the best performer in vertical accuracy, with a small mean error (ME) of 0.9 m and a root mean squared error (RMSE) of 12.6 m, followed by AW3D30 (2.6 m ME and 11.3 m RMSE). TanDEM-X also performs well (0.1 m ME and 15.1 m RMSE) but suffers from serious errors and outliers on steep slopes. SRTM-based DEMs (SRTM-GL1, SRTM v4.1, and MERIT) (13.5–17.0 m RMSE) had an inferior performance to NASADEM. Errors in the six DEMs increase from the south-facing to the north-facing aspect and become larger with increasing slope. Misregistration of the six DEMs relative to the ICESat-2 footprint in most glacier areas is small (less than one grid spacing). In a next step, the influence of six DEMs on four ice-thickness inversion models – GlabTop2 (Glacier bed Topography), Open Global Glacier Model (OGGM), Huss–Farinotti (HF), and Ice Thickness Inversion Based on Velocity (ITIBOV) – is intercompared. The results show that GlabTop2 is sensitive to the accuracy of both elevation and slope, while OGGM and HF are less sensitive to DEM quality and resolution, and ITIBOV is the most sensitive to slope accuracy. NASADEM is the best choice for ice-thickness estimates over the whole TP. [ABSTRACT FROM AUTHOR]

Variations in glacier meltwater in the source regions of the Tibetan Plateau's (TP) largest lake (Selin Co) and China's longest river (Yangtze River) regulate the local and downstream water balance under the warming climate. However, the magnitude of their variations over the past four decades is still unknown. Here, we examine long-term changes in glacier mass balance over 1976–2017 using KH-9 and CoSSC-TanDEM-X data. We find that the mean rate of glacier mass loss (GML) has accelerated from −0.21 ± 0.11 m a–1 over 1976–2000, to −0.28 ± 0.14 m a–1 over 2000–11, and subsequently to −0.48 ± 0.10 m a–1 over 2011–17. Changes in temperature and precipitation are the major causes of GML. Over 1976–2017, the contribution of decadal GML to Tuotuohe sub-basin runoff ranges from 4.3 to 8.0%, while its contribution to increased lake volume change in Selin Co and Chibzhang Co-Dorsoidong Co ranges from 3.5 to 16.3% and 19.2 to 21.4%, respectively. The GML of source regions made relatively small contributions to river runoff and lake supply, but plays a vital role when precipitation decreases. The quantitative evaluation of the water balance for the sources of great rivers and lakes over the TP is therefore important for water resource management and hydrological cycle studies. [ABSTRACT FROM AUTHOR]

Subseasonal-to-seasonal (S2S) prediction, especially the prediction of extreme hydroclimate events such as droughts and floods, is not only scientifically challenging, but also has substantial societal impacts. Motivated by preliminary studies, the Global Energy and Water Exchanges (GEWEX)/Global Atmospheric System Study (GASS) has launched a new initiative called "Impact of Initialized Land Surface Temperature and Snowpack on Subseasonal to Seasonal Prediction" (LS4P) as the first international grass-roots effort to introduce spring land surface temperature (LST)/subsurface temperature (SUBT) anomalies over high mountain areas as a crucial factor that can lead to significant improvement in precipitation prediction through the remote effects of land–atmosphere interactions. LS4P focuses on process understanding and predictability, and hence it is different from, and complements, other international projects that focus on the operational S2S prediction. More than 40 groups worldwide have participated in this effort, including 21 Earth system models, 9 regional climate models, and 7 data groups. This paper provides an overview of the history and objectives of LS4P, provides the first-phase experimental protocol (LS4P-I) which focuses on the remote effect of the Tibetan Plateau, discusses the LST/SUBT initialization, and presents the preliminary results. Multi-model ensemble experiments and analyses of observational data have revealed that the hydroclimatic effect of the spring LST on the Tibetan Plateau is not limited to the Yangtze River basin but may have a significant large-scale impact on summer precipitation beyond East Asia and its S2S prediction. Preliminary studies and analysis have also shown that LS4P models are unable to preserve the initialized LST anomalies in producing the observed anomalies largely for two main reasons: (i) inadequacies in the land models arising from total soil depths which are too shallow and the use of simplified parameterizations, which both tend to limit the soil memory; (ii) reanalysis data, which are used for initial conditions, have large discrepancies from the observed mean state and anomalies of LST over the Tibetan Plateau. Innovative approaches have been developed to largely overcome these problems. [ABSTRACT FROM AUTHOR]

Monitoring changes in river runoff at the Third Pole (TP) is important because rivers in this region support millions of inhabitants in Asia and are very sensitive to climate change. Under the influence of climate change and intensified cryospheric melt, river runoff has changed markedly at the TP, with significant effects on the spatial and temporal water resource distribution that threaten water supply and food security for people living downstream. Despite some in situ observations and discharge estimates from state-of-the-art remote sensing technology, the total river runoff (TRR) for the TP has never been reliably quantified, and its response to climate change remains unclear. As part of the Chinese Academy of Sciences' "Pan-Third Pole Environment Study for a Green Silk Road," the TP-River project aims to construct a comprehensive runoff observation network at mountain outlets (where rivers leave the mountains and enter the plains) for 13 major rivers in the TP region, thereby enabling TRR to be accurately quantified. The project also integrates discharge estimates from remote sensing and cryosphere–hydrology modeling to investigate long-term changes in TRR and the relationship between the TRR variations and westerly/monsoon. Based on recent efforts, the project provides the first estimate (656 ± 23 billion m3) of annual TRR for the 13 TP rivers in 2018. The annual river runoff at the mountain outlets varies widely between the different TP rivers, ranging from 2 to 176 billion m3, with higher values mainly corresponding to rivers in the Indian monsoon domain, rather than in the westerly domain. [ABSTRACT FROM AUTHOR]

Sub-seasonal to seasonal (S2S) prediction, especially the prediction of extreme hydroclimate events such as droughts and floods, is not only scientifically challenging but has substantial societal impacts. Motivated by preliminary studies, the Global Energy and Water Exchanges (GEWEX)/Global Atmospheric System Study (GASS) has launched a new initiative called Impact of initialized Land Surface temperature and Snowpack on Sub-seasonal to Seasonal Prediction (LS4P), as the first international grass-root effort to introduce spring land surface temperature (LST)/subsurface temperature (SUBT) anomalies over high mountain areas as a crucial factor that can lead to significant improvement in precipitation prediction through the remote effects of land/atmosphere interactions. LS4P focuses on process understanding and predictability, hence it is different from, and complements, other international projects that focus on the operational S2S prediction. More than forty groups worldwide have participated in this effort, including 21 Earth System Models, 9 regional climate models, and 7 data groups. This paper overviews the history and objectives of LS4P, provides the first phase experimental protocol (LS4P-I) which focuses on the remote effect of the Tibetan Plateau, discusses the LST/SUBT initialization, and presents the preliminary results. Multi-model ensemble experiments and analyses of observational data have revealed that the hydroclimatic effect of the spring LST in the Tibetan Plateau is not limited to the Yangtze River basin but may have a significant large-scale impact on summer precipitation and its S2S prediction. LS4P models are unable to preserve the initialized LST anomalies in producing the observed anomalies largely for two main reasons: i) inadequacies in the land models arising from total soil depths which are too shallow and the use of simplified parameterizations which both tend to limit the soil memory; and ii) reanalysis data, that are used for initial conditions, have large discrepancies from the observed mean state and anomalies of LST over the Tibetan Plateau. Innovative approaches have been developed to largely overcome these problems. [ABSTRACT FROM AUTHOR]

The lower parts of two glaciers in the Aru range on the western Tibetan Plateau (TP) collapsed on 17 July and 21 September 2016, respectively, causing fatal damage to local people and their livestock. The giant ice avalanches, with a total volume of 150 × 10 6 m 3 , had almost melted by September 2019 (about 30 % of the second ice avalanche remained). The impact of these extreme disasters on downstream lakes has not been investigated yet. Based on in situ observation, bathymetry survey and satellite data, we explore the impact of the ice avalanches on the two downstream lakes (i.e., Aru Co and Memar Co) in terms of lake morphology, water level and water temperature in the subsequent 4 years (2016–2019). After the first glacier collapse, the ice avalanche slid into Aru Co along with a large amount of debris, which generated great impact waves in Aru Co and significantly modified the lake's shoreline and underwater topography. An ice volume of at least 7.1 × 10 6 m 3 was discharged into Aru Co, spread over the lake surface and considerably lowered its surface temperature by 2–4 ∘ C in the first 2 weeks after the first glacier collapse. Due to the large amount of meltwater input, Memar Co exhibited more rapid expansion after the glacier collapses (2016–2019) than before (2003–2014), in particular during the warm season. The melting of ice avalanches was found to contribute to about 23 % of the increase in lake storage between 2016 and 2019. Our results indicate that the Aru glacier collapses had both short-term and long-term impacts on the downstream lakes and provide a baseline in understanding the future lake response to glacier melting on the TP under a warming climate. [ABSTRACT FROM AUTHOR]

During the last glacial termination, a warming trend was generally interrupted by rapid millennium-scale cold reversals, such as the Greenland (Isotope) Stadial 1 (GS-1) and GS-2a events. To understand how glaciers on the Tibetan Plateau (TP) responded to these rapid climate events, this study constrained the timing and extent of three glacial events during the late-glacial period. Specifically, using a cosmogenic 10Be exposure dating method, we dated three prominent glacial moraines (PM1, PM2, PM3) back to 15,850 ± 980, 14,140 ± 880, and 12,430 ± 790 yr in the Pagele valley, southern TP, corresponding to GS-2a, Greenland Interstadial 1 (GI-1), and GS-1, respectively. By simulating glacial extents forced by different climate scenarios, the study constrained the temperature decreases relative to present to be 2.6°C–2.9°C, ~1.6°C, and 1.4°C–1.5°C during the GS-2a, GI-1, and GS-1 periods in the region, with precipitation values of 60%–80%, ~100%, and 80%–90% of present value, respectively. Considering information from oceanic and atmospheric circulation, the study suggested that on the TP, the glacial events during the last glacial termination were well connected with the millennium-scale climate events in the North Atlantic region through the westerlies, while the Indian summer monsoon played a positive role in sustaining the glaciers under the warming climate trend. [ABSTRACT FROM AUTHOR]

A well‐preserved Last Glacial Maximum (LGM) moraine set in the Quemuqu Valley on the eastern slope of the Qiongmu Gangri Peak offers great potential for reconstructing LGM glacier extent and examining LGM climate in the region. This study employed a coupled and physics‐based mass balance and ice‐flow model to investigate glacier sensitivities to climate in the valley. Based on the sensitivity tests and the well‐preserved LGM moraines, the study also reconstructed the LGM glacier extent in the valley and assessed the magnitude of cooling for the LGM period. Model results suggest that the Quemuqu Valley sustained an ice volume of 6.80±0.16 km3 in the LGM period. Temperature depression of 3.1–4.3 °C, combined with 30–70% modern precipitation, is likely to have supported the LGM glacier extent in the valley. The temperature inference for the LGM period is comparable with other independent palaeoclimate evidence in the region. However, there is a large difference in the reconstructed glacier volume (ice thickness) between previous research and the current study. The glacier model used here directly calculates the ice thickness and needs relatively less field evidence to constrain the model simulations. It is therefore advocated to use such a model to reconstruct past glaciers and their corresponding climates for other valleys of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

This study evaluates the monthly, seasonal, and annual characteristics of near-surface air temperature as a function of both elevation and geographical coordinates over Pakistan, using a climatic data set from 53 observation stations ranging between 5 and 2317 m asl and stepwise multiple regression. Forcing processes for temperature gradient (TG) variation were determined by analyzing its relationship with moisture flux (qv) and gradients of rainfall and saturation vapor pressure (es). The bi-model pattern of TGE (temperature gradient with topographic elevation), which earlier studies (TAAC 113(3):671-682, TAAC 132:1129-1141) from the southern slopes of the Himalayas have observed, is also consistent in this study region. However, the forcing strengths, mechanisms, and processes for the monthly variations in TGs magnitude and their diurnal range are somewhat different. The annual cycle of TGE in this study is inversely (positively) associated with the rainfall (es) gradient. Monsoon and orographic controls for TGE are stronger in summer, especially in the day, while the influences of inversions and mountainous topoclimate are higher during the non-monsoon period, in particular in winter and at night. Mountain barrier effects are higher in summer, which considerably hamper the relationship between temperature and geographical coordinates and rainfall and elevations. Steeper values of mean TGEs in the non-monsoon period are the result of strong dry convectional cooling at higher elevations due to high thermal forcing effects at lower elevations. Sensible heating reduction due to westerly-driven precipitation and cloud cover in daytime in the northern mountainous region (or higher latitudes) further strengthens the TGE value in this period. This effect is weaker in the surrounding regions; therefore, the TGE magnitude in this study is expected to be higher, especially in the pre-monsoon season. Gradients are more shallow in winter (excluding latitude), but values are greater than those in summer, due to distinct variations in moisture and cloud amount, i.e., lower in winter and higher in summer, particularly at lower elevations. Observed distinct differences in TG diurnal range between elevation (high) and latitude (low) in this study are due to a wide variation in temperature, topography, and elevations within the same latitudinal belts. In this study, the lowest gradient values for elevation are observed in August and the highest in May, 1 month later than observed in adjacent mountain regions due to the late arrival of monsoon moisture in summer and intense thermal forcing effects following the wet early pre-monsoon months. Distinct variability of gradient magnitudes between the northern mountainous region and the southern flat terrain is due to differences in topoclimates, moisture amounts, elevations, and geographical coordinates. [ABSTRACT FROM AUTHOR]

This study investigates the daily, monthly, and seasonal characteristics of precipitation and associated forcing processes for their spatial-temporal variations over two geographically distinct river basins (Kaligandaki and Koshi) in Nepal, located on the southern slopes of the central Himalayas. A 34-year (1981–2015) daily precipitation data set of 49 stations between the elevation ranges of 143 to 3870 m asl was used for this investigation. The Gini coefficient, and index, degree and period of precipitation concentrations, and rainfall gradients were derived to examine precipitation distribution characteristics and causes for their variation. A rapid decrease of rainfall with elevation was observed in the Kaligandaki basin throughout the period of record, while this pattern was reversed in the Koshi basin, due to the rain shadow and orographic effects, which is pronounced in the monsoon season. Mountain effects are likely responsible for the distinct differences in daily and monthly precipitation distribution, with irregular patterns observed in the northern region of Kaligandaki basin and southern region in Koshi basin, with uniform patterns in the southern region of Kaligandaki basin and the northern region of Koshi basin. There is also a distinct variation in seasonality, which is higher (concentrated over several months) in the central northern region in Kaligandaki basin and less concentrated in the northern region of Koshi basin. But monthly precipitation characteristics in the western portion of Koshi and the southern region of Kaligandaki basins show high variability and short concentration duration. However, the months when precipitation is concentrated differed between the basins: from late July to August in Kaligandaki and June to September in Koshi basin. This is because the monsoon arrives later in the west than in the eastern part of the country. Variation in number of rainy days is higher in Koshi, but rainfall amount is greatest in Kaligandaki basin due to its proximity to the ocean and the intense effect of the monsoon. In addition to its value for rainfall-induced disaster mitigation strategies and management planning, this study will be useful for hydrological modeling in these areas in the future. [ABSTRACT FROM AUTHOR]

Elevational gradients are powerful 'natural laboratory' for testing the responses of microbes to geophysical influences. Microbial communities are normally composed of a few abundant and many rare taxa. Abundant and rare taxa play different ecological roles in kinds of environments, but how their diversity and composition patterns response to elevation gradients is still poorly elucidated. In this study, we investigated the elevational patterns of abundant and rare bacterial diversity and composition in a mountain stream from 712 to 3435 m at Gangrigabu Mountain on the Tibetan Plateau, China. Our results revealed abundant and rare bacteria had similar decreasing elevation trend of alpha diversity, and both of them showed a significant elevational distance-decay relationship. However, the turnover rate of the elevational distance-decay of rare bacteria was higher than that of abundant bacteria. The species-abundance distribution patterns of rare taxonomic composition were associated with the elevational gradient, while most of abundant bacterial clades did not display any relationships with elevation. Our results suggested that rare bacteria were more sensitive to changes in elevation gradient. [ABSTRACT FROM AUTHOR]

The Third Pole (TP) is experiencing rapid warming and is currently in its warmest period in the past 2,000 years. This paper reviews the latest development in multidisciplinary TP research associated with this warming. The rapid warming facilitates intense and broad glacier melt over most of the TP, although some glaciers in the northwest are advancing. By heating the atmosphere and reducing snow/ice albedo, aerosols also contribute to the glaciers melting. Glacier melt is accompanied by lake expansion and intensification of the water cycle over the TP. Precipitation has increased over the eastern and northwestern TP. Meanwhile, the TP is greening and most regions are experiencing advancing phenological trends, although over the southwest there is a spring phenological delay mainly in response to the recent decline in spring precipitation. Atmospheric and terrestrial thermal and dynamical processes over the TP affect the Asian monsoon at different scales. Recent evidence indicates substantial roles that mesoscale convective systems play in the TP's precipitation as well as an association between soil moisture anomalies in the TP and the Indian monsoon. Moreover, an increase in geohazard events has been associated with recent environmental changes, some of which have had catastrophic consequences caused by glacial lake outbursts and landslides. Active debris flows are growing in both frequency of occurrences and spatial scale. Meanwhile, new types of disasters, such as the twin ice avalanches in Ali in 2016, are now appearing in the region. Adaptation and mitigation measures should be taken to help societies' preparation for future environmental challenges. Some key issues for future TP studies are also discussed. [ABSTRACT FROM AUTHOR]

Abstract Glacier surface ablation and associated energy characteristics are important to glacier survival, but little is known about these on glaciers in the West Kunlun Mountains (WKM), Tibetan Plateau, mainly due to their inaccessibility. Based on the glacio-meteorological conditions and mass balance observations on the Guliya ice cap (GIC) in the WKM during 2015/'16, a distributed energy and mass balance model was applied to study the spatiotemporal variations of energy and mass balance on the GIC, and the response of mass balance to climate change. Modeled results revealed that compared to the Chongce glacier in the WKM which was observed to undergo a positive mass balance in the 1980s, the GIC suffered a small mass loss with an annual value of −0.193 ± 0.042 m water equivalent, and the equilibrium-line altitude has risen by approximately 70 m to locate at 6000 ± 19 m. Besides, over the entire observation period, the incoming energy supplied by net shortwave radiation was almost balanced by the energy loss through net longwave radiation, and most energy available for surface ablation was consumed by latent heat flux through sublimation, which became a significant feature of the energy balance on the GIC. Sensitivity experiments by changing model input data with synthetic climate scenarios, which were sampled from meteorological measurements and accounted for coupled climate variable perturbations, revealed that the mass balance of the GIC was more sensitive to the changes in moisture-related variables than that in temperature, and positive mass balance would only be given from scenarios with significantly increased annual precipitation and decreased air temperature compared to those observed in 2015/'16. Highlights • Mass balance and meteorological conditions were investigated on the Guliya ice cap (GIC) from September 2015 to October 2016. • Modeling results revealed that the GIC is presently suffering from mass loss in 2015/16. • The mass balance of the GIC was more sensitive to moisture-related changes than to air temperature change. • Climate conditions (cold and wet during 2000–2016) were conducive to the survival of glaciers in the WKM'. [ABSTRACT FROM AUTHOR]

Abstract Lakes are sensitive indicators of anthropogenic climate change and also respond to direct human activities. Yet, long-term lake inventories and quantitative evaluation of the factors driving observed lake changes across China remain elusive. Here, for the first time, we examined multi-decadal lake area changes in China during 1960s–2015, using historical topographic maps and >3831 Landsat satellite images, including lakes as fine as ≥1 km2 in size. In addition, we quantified the causes of lake changes from climatic and anthropogenic factors. The total area of lakes in China has increased by 5858.06 km2 (9%) between 1960s and 2015, and with heterogeneous spatial variations. Lake area changes in the Tibetan Plateau, Xinjiang, and Northeast Plain and Mountain regions reveal significant increases of 5676.75, 1417.15, 1134.87 km2 (≥15%), respectively, but the Inner-Mongolian Plateau shows an obvious decrease of 1223.76 km2 (22%). We find that 141 new lakes have appeared predominantly in the arid western China; but 333 lakes, mainly located in the humid eastern China, have disappeared over the past five decades. We conclude that climate factors have played a dominant role in lake changes across China, coupled with noticeable anthropogenic contribution of ~35% in the Eastern Plain and Yunnan-Guizhou Plateau. This study has substantial implications to improve decision support regarding water-resource management strategies and land-use planning throughout China. Highlights • Produced a comprehensive China lake dataset from the 1960s to 2015 • Total lake area increased by 9% over five decades with evident regional differences • New lakes and lake area expansion in the arid western China due to climate change • Disappeared and shrinking lakes in the humid eastern China due to human activity [ABSTRACT FROM AUTHOR]

Graphic abstract Abstract The environmental significance of levoglucosan (LEV) records in Tibetan glacier ice layers on sub-annual to annual scales, in particular their suitability as a specific biomarker for indicating past fire changes, is poorly understood at present. In this work, a continuous LEV record was reconstructed in a central Tibetan ice core for the period 1990–2012. The LEV record was classified into two categories based on its LEV concentrations: background levels and extreme events. Annually-resolved LEV records and background levels in the ice core were strongly correlated with satellite observations of fire occurrence frequency over the northern Indian peninsula between 2003 and 2012, especially for strong fire events during the pre-monsoon season (March–May). In addition, peaks in LEV concentrations may represent extreme fire events in regions around the Tibetan Plateau. LEV records in the ice core reflect a long-term increasing trend in fire background and also an increase in fire extreme events, across the Tibetan Plateau and its surroundings. We therefore conclude that LEV records in Tibetan ice cores can be used as a powerful tool for calibrating and reconstructing past fire changes over subtropical Asia. [ABSTRACT FROM AUTHOR]

Abstract Understanding rainfall characteristics plays a vital role in sustainable watershed development and management, but at the same time it is challenging in mountainous regions, due to its topography complexities. This study investigates the seasonal along its associated months and annual rainfall characteristics and their variations over two distinct river basins; Kaligandaki in central west and Koshi in eastern Nepal, located on the southern slopes of the central Himalayas, which is crucial to the research of the climate change in these regions. The rainfall data series over the period of 34-year (1981–2015) of 43 stations between the elevation range of 143 m asl to 3870 m asl was used for this study. The analysis was carried out to assess the significance of rainfall trend along with its magnitude followed by its abrupt shift by using the Mann-Kendall test, Sen's test and Sequential Mann-Kendall test respectively. Furthermore, multitaper method was used to confirm the influence of large-scale circulation indices over the study area. An increasing pattern of rainfall from south to north was observed throughout all season in Koshi basin which was not seen in the Kaligandaki basin, indicating the effects of orography along with monsoon. Both basins share a similar pattern of rainfall between annual and monsoonal rainfall, supporting that both basins are dominated by the monsoon. The transition months between the seasons showed almost similar spatial distribution but different from other months of respective seasons. The results showed that the seasonal and annual rainfall declined in most of the stations of both the basins, except during pre-monsoon where it showed increased rainfall. But only a few stations showing such changes were statistically significant. In fact, these noticeable significant decreases were observed especially in the southern and northern region of Koshi basin while in Kaligandaki basin, it was found either in central or in the southern region. Furthermore, the trend shift analysis identified change points during 1980s or early 1990s, but most significant shifts were observed in recent years with some exceptions. Spectral analysis showed significant peaks at periodicity ranging 2–5 years, suggesting a potential association with Quasi-Biennial Oscillations (QBO) and El Niño-Southern Oscillation (ENSO). Highlights • The spatial distribution of rainfall along with their trend were investigated. • Seasonal and annual rainfall declined in most of the stations with only few stations showing statistically significant. • Significant decreases were observed in the southern and northern (central/southern) region of Koshi (Kaligandaki) basin. • Abrupt change point were observed during 80's or early 90's, but most significant shifts were observed in recent years. • Both basins showed connection of rainfall with large-scale circulation indices. [ABSTRACT FROM AUTHOR]

To further our understanding of the Asian monsoon system, particularly the onset dates of monsoon sub-systems over their respective East Asian domains, we present an 8-year (2007-2014) dataset of oxygen isotopes of precipitation (δ18Op) from three stations, Lulang and Nuxia in southeastern Tibetan Plateau (SETP) and Guangzhou in southeastern coastal China (SECN). The general agreement between isotopically identified monsoon onset dates with those identified by the meridional temperature gradient suggests that the initially sustained isotopic depletion is sensitive to the evolving thermal contrast between the Eurasian continent and the Indian Ocean. The 850 hPa meridional wind over nearby oceans is an efficient bridge linking isotopic variations in both regions with their respective monsoon sub-systems. The intensity of the South Asian High and tropical cyclone frequencies show stronger effects on isotopic depletion in the SECN than in the SETP and on monsoon onset timing over the South China Sea. Tibetan Plateau snow cover anomalies are significantly correlated with δ18Op in both regions on monthly timescales. [ABSTRACT FROM AUTHOR]

Since the late 1990s, lakes in the southern Tibetan Plateau (TP) have shrunk considerably, which contrasts with the rapid expansion of lakes in the interior TP. Although these spatial trends have been well documented, the underlying hydroclimatic mechanisms are not well understood. Since 2013, we have carried out comprehensive water budget observations at Paiku Co, an alpine lake in the central Himalayas. In this study, we investigate water storage and lake level changes on seasonal to decadal time scales based on extensive in-situ measurements and satellite observations. Bathymetric surveys show that Paiku Co has a mean and maximum water depth of 41.1 m and 72.8 m, respectively, and its water storage was estimated to be 109.3 × 10 8 m 3 in June 2016. On seasonal scale between 2013 and 2017, Paiku Co’s lake level decreased slowly between January and May, increased considerably between June and September, and then decreased rapidly between October and January. On decadal time scale, Paiku Co’s lake level decreased by 3.7 ± 0.3 m and water storage reduced by (10.2 ± 0.8) × 10 8 m 3 between 1972 and 2015, accounting for 8.5% of the total water storage in 1972. This change is consistent with a trend towards drier conditions in the Himalaya region during the recent decades. In contrast, glacial lakes within Paiku Co’s basin expanded rapidly, indicating that, unlike Paiku Co, glacial meltwater was sufficient to compensate the effect of the reduced precipitation. [ABSTRACT FROM AUTHOR]

• Unprecedented lake expansion occurred in 2017–2018 on the inner Tibetan Plateau. • The rapid lake expansion exerted a significant impact on regional ecosystems and human living environments. • The rapid lake expansion was mainly attributed to anomalously high precipitation. Extreme events on the Tibetan Plateau (TP) have become increasingly frequent and severe in recent decades in tandem with rapid climate warming and moistening. Thus, it is highly important to investigate their processes, causes and environmental impacts. Using in-situ observations of lake level changes in combination with satellite altimetry data, we showed that lakes on the central TP (CTP) expanded unprecedentedly in 2017–2018, with lake level increases of 1.4–2.8 m at the five observed lakes. This extreme lake expansion occurred over almost the entire inner TP, which was mainly attributed to anomalously high precipitation (approximately 43–97% higher in 2017–2018 than in normal years on the CTP). The rapid lake expansion posed a substantial threat to regional ecosystems, infrastructure, and even residential habitats. Therefore, it is necessary to identify the potential sites threatened by lake expansion on the TP using high-resolution satellite images and perform near real-time observations of lake level changes through satellite and in-situ observations. [ABSTRACT FROM AUTHOR]

Spatial and temporal variability in stable isotopic compositions (δ 18 O and δD) in river water of the Yarlungzangbo was investigated to identify major hydrological processes along the river channel and evaluate the isotopic response to discharge variation. The results show geographic, distinct isotopic evolutions in the Yarlungzangbo system. Along the main stem, river δ 18 O exhibits a decreasing trend from the headwaters to the middle reach but an increasing one from the middle to the lower reaches, and main flows demonstrate much greater δ 18 O-δD slope and intercept compared to the global meteoric water line (GMWL) and reported local meteoric water lines (LMWLs) for sites within the basin. These results are found to be consistent with the isotopic characteristics of stream and river waters collected across the entire drainage basin. Water mixing appears to be the dominant hydrological process along the Yarlungzangbo, and the pattern of isotopic change in individual river reaches closely reflects that of precipitation in corresponding part of the river basin. The isotopic variability along the main stem observed during the synoptic survey is evidenced to hold through time by a time-series investigation at three key hydrological stations. River water at such three stations shows a strong isotopic response to discharge variability. In general, river δ 18 O tends to be negatively correlated with discharge, highlighting a typical monsoon precipitation-driven isotope-discharge pattern. Specifically, we found their individual discharge-weighted average δ 18 O values likely vary in a similar rate with the ratio of mean discharge in monsoon season (JAS) to that in pre-monsoon season (MJ) on a yearly basis, indicating a specific relationship between average river isotopic composition and discharge seasonality throughout their drainage areas (i.e. the middle-lower Yarlungzangbo basin). This study thus demonstrates the usefulness of isotopic data for assessing hydrodynamics over a less explored, complex and high-altitude large river catchment. [ABSTRACT FROM AUTHOR]

Records of recent climate from ice cores drilled in 2015 on the Guliya ice cap in the western Kunlun Mountains of the Tibetan Plateau, which with the Himalaya comprises the Third Pole (TP), demonstrate that this region has become warmer and moister since at least the middle of the 19th century. Decadal-scale linkages are suggested between ice core temperature and snowfall proxies, North Atlantic oceanic and atmospheric processes, Arctic temperatures, and Indian summer monsoon intensity. Correlations between annual-scale oxygen isotopic ratios (δ 18 O) and tropical western Pacific and Indian Ocean sea surface temperatures are also demonstrated. Comparisons of climate records during the last millennium from ice cores acquired throughout the TP illustrate centennial-scale differences between monsoon and westerlies dominated regions. Among these records, Guliya shows the highest rate of warming since the end of the Little Ice Age, but δ 18 O data over the last millennium from TP ice cores support findings that elevation-dependent warming is most pronounced in the Himalaya. This, along with the decreasing precipitation rates in the Himalaya region, is having detrimental effects on the cryosphere. Although satellite monitoring of glaciers on the TP indicates changes in surface area, only a few have been directly monitored for mass balance and ablation from the surface. This type of ground-based study is essential to obtain a better understanding of the rate of ice shrinkage on the TP. [ABSTRACT FROM AUTHOR]

Nam Co (Heavenly Lake) not only responds sensitively to climate change, but also exerts significant influences on climate change. Previous studies revealed that the lake effects from the North American Great Lakes shown interaction with climate changes. However, the lakes effect of more than 1200 lakes with an area of 47,000 km 2 on the Tibetan Plateau remains less studied. In this study, we analyzed the spatial distribution of precipitation in the Nam Co Basin during July–August and November–December to clarify the lake effect. We found that the lake cooling effect during July–August and lake heating effect during November–December resulted in the spatial differences of precipitation within the Nam Co Basin. These effects generally caused more precipitation in the south than in the north during July–August, and more precipitation in the east than in the west during November–December. Weakening Indian monsoon and climate warming led to an increased north–south precipitation difference in the Nam Co Basin. However, the precipitation differences between the west and east during November–December decreased with climate warming. The intensification of the westerly might be responsible for the particular phenomenon. [ABSTRACT FROM AUTHOR]

Glacier mass balance shows a spatially heterogeneous pattern in response to global warming on the Tibetan Plateau (TP), and the climate mechanisms controlling this pattern require further study. In this study, three glaciers where systematic glaciological and meteorological observations have been carried out were selected, specifically Parlung No. 4 (PL04) and Zhadang (ZD) glaciers on the southern TP and Muztag Ata No. 15 (MZ15) glacier in the eastern Pamir. The characteristics of the mass and energy balances of these three glaciers during the periods between October 1th, 2008 and September 23rd, 2013 were analyzed and compared using the energy and mass balance model. Results show that differences in surface melt, which mainly result from differences in the amounts of incoming longwave radiation (Lin) and outgoing shortwave radiation (Sout), represent the largest source of the observed differences in mass balance changes between PL04 and ZD glaciers and MZ15 glacier, where air temperature, humidity, precipitation and cloudiness are dramatically different. In addition, sensitivity experiments show that mass balance sensitivity to air temperature change is remarkably higher than that associated with precipitation change on PL04 and ZD glaciers, in contrast results from MZ15 glacier. And significantly higher sensitivities to air temperature change are noted for PL04 and ZD glaciers than for MZ15 glacier. These significant differences in the sensitivities to air temperature change are mainly caused by differences in the ratio of snowfall to precipitation during the ablation season, melt energy (Lin+Sout) during the ablation season and the seasonality of precipitation among the different regions occupied by glaciers. In turn, these conditions are related to local climatic conditions, especially air temperature. These factors can be used to explain the different patterns of change in Tibetan glacier mass balance under global warming. [ABSTRACT FROM AUTHOR]

Based on climatic data from 18 stations on the southern slopes of the eastern Himalayas in Bhutan for the period from 1996 to 2009, this paper investigates monthly characteristics of the near-surface air temperature lapse rate (TLR). The station elevations used in this study range from 300 to 2760 m a. s. l. TLRs were evaluated using a linear regression model. The monthly values of maximum TLRs were always smaller than those of the minimum TLRs, which is in contrast to results from the surrounding mountainous regions. In this study, annual patterns of TLRs were somewhat consistent, particularly in the summer; during the other seasons, patterns contrasted to results from the southeastern Tibetan Plateau (China) and were almost comparable to results from Nepal. The shallowest observed values for TLRs in summer are due to intense latent heating at the higher elevation, associated with water vapor condensation from moist convection and evapotranspiration, and decreasing sensible heating at lower elevation, due to heavier rainfall, cloud, and forest cover. When compared to summer, the steeper TLRs in the non-monsoon season are due to sensible heating at the lower elevations, corresponding to dry and clear weather seasons, as well as increasing cooling at higher elevations, particularly in winter due to snow and cloud cover. Owing to lower albedo and higher aerodynamic roughness of forested areas, the TLRs were considerably reduced in daytime because of the dissipation of sensible heat to the atmospheric boundary layer. The distinct variation in diurnal TLR range is due to the diurnal variation in net radiation associated with reduced turbulent heating in the day and increased turbulent heating in the night, in addition to the effect of moisture and cloud cover. The shallower values of TLRs in this study when compared with the surrounding mountainous regions are due to high humidity, as well as the differing elevations and local climates. [ABSTRACT FROM AUTHOR]

ABSTRACT: This study quantifies the spatial–temporal distribution of the near‐surface temperature lapse rate (TLR) on the southeastern Tibetan Plateau (SETP) on the northern slopes of the eastern Himalayas, using the jackknife regression model. A 20‐year (1985–2004) climatic data set of 16 stations between the elevation range of 3553–4801 m asl was used for this investigation. Controls for the spatial–temporal variation on TLRs and causes of higher mean square error (MSE) from the jackknife regressions were also analysed. Dry convection due to increasing sensible heating at lower elevations associated with clear skies, the effect of cold air surges, cloud/fog, as well as pronounced long‐wave radiation loss due to snow cover at higher elevation, results in the super‐dry adiabatic TLR in the dry winter. In response to the effects of high rainfall and humidity, intense latent heating at higher elevation due to moist adiabatic cooling causes TLRs to decrease significantly in summer. The variation in net radiation due to differences in moisture, rainfall, cloud cover and air mass between higher (fewer) and lower (higher) elevations further contributes to reducing TLRs values in this season. Observed steeper values of TLRs at higher elevations and more shallow values at lower elevations are due to the thermal contrast between snow‐free ground and snow‐covered mountain terrain, as well as the effect of variations in air mass and moisture. Based on derived values, this article also estimates near‐surface temperature at higher elevations and analyses the precision of estimated values. Measurement of the lowest discrepancy (bias) between observed and estimated values from this study suggests that the estimation skills of the model are good enough. More precisely, including the smallest MSE from the jackknife regression and biases of the estimated values can be made for summer, perhaps due to the moisture controlled throughout the SETP, i.e. associated with the Indian monsoon. Higher MSE and biases are observed during winter and are due to the substantial effects of westerlies, as well as the station's geographical coordinate, local topography and microclimate. The MSE and the estimated biases are lowest at high‐elevation stations and are associated with the lower contaminating effects of the surface. This estimation model, using derived values from this investigation, could be useful for glacier‐hydro‐climatic and ecological modelling in this region. [ABSTRACT FROM AUTHOR]

The mass-balance of Muztag Ata No. 15 (MZ15) glacier in the eastern Pamir is reconstructed between 1980 and 2012 using an energy-based mass-balance model. The results show that this glacier has been characterized by obvious interannual mass-balance changes during 1980–2012 with a slightly positive mass balance during 1998–2012. Precipitation in the ablation season is a primary driver of these mass-balance fluctuations. Distinct changes in the mass-balance of MZ15 glacier between 1980–1997 and 1998–2012 are thought to be associated with changes in the regionally averaged meridional wind speed and corresponding precipitation in the ablation season. The negative and positive mass-balance phases during 1980–1997 and 1998–2012, respectively, were associated with northerly and southerly wind anomalies in the eastern Pamir and their corresponding decreasing and increasing precipitation. These changes in circulation appear to be linked to the mid-latitude climate. Finally, contrary to the variation of most glaciers on the Tibetan Plateau, glaciers in the Karakoram-western Kunlun-eastern Pamir appear to have retreated more slowly over the past 10 years than during the 1970s-2000. This contrasting trend may be caused by different changes in snowfall and different topography factors in different regions under warming and increased precipitation. [ABSTRACT FROM AUTHOR]

Glaciers on the Tibetan Plateau (TP) exist in different states of extension and retreat, responding to the westerly winds and Indian monsoon. However, few studies to-date have focused on climate change in the westerlies-dominated northwest TP. Here, we report an ice core climate record during the last century retrieved from the Kuokuosele (KKSL) Glacier in the westerlies-dominated eastern Pamir, northwest TP. The ice core has dated based on annual layer counting using ice core δ 18 O seasonal cycles, constrained by both the beta (β) activity peak and 137 Cs concentration peak in 1962/63. Reconstruction of δ 18 O and annual accumulation from the ice core and comparison with observed temperature and precipitation at nearby meteorological stations as well as CRU (Climate Research Unit) data confirm their climatic and regional significance. Both ice core δ 18 O and accumulation increased during the last century, thus pointing to a warming and wetting trend in the westerlies dominated northwest TP. [ABSTRACT FROM AUTHOR]

Containing elevated topography, the Tibetan Plateau (TP) has significant thermodynamic effects for regional environment and climate change, where understanding energy and water exchange processes (EWEP) is an important prerequisite. However, estimation of the exact spatiotemporal variability of the land-atmosphere energy and water exchange over heterogeneous landscape of the TP remains a big challenge for scientific community. Focused on the above scientific question, a series of atmospheric scientific experiments and research programs have been conducted since the 1960s, quantitatively evaluating both the spatial distribution and the multi-timescale variation of EWEP via observation, remote sensing, and numerical simulation. Based on the three main approaches, the major advances on EWEP over the past 25 years are systematically summarized in this work. Observations reveal distinct characteristics of the energy balance components and micrometeorological parameters. The roughness length for momentum is generally one order of magnitude higher than that for heat, and a distinct diurnal cycle of the excess resistance for heat transfer (kB −1) is captured. These progresses via observations further contributed to the improvement of remote sensing parameterization and numerical simulation of EWEP, e.g., the daily sensible heat flux can be overestimated by approximately 50% using a fixed kB −1, while this overestimation can be mitigated with the observation-captured diurnal variation in kB −1 taken into consideration. Moreover, multisource (multispectral, thermal, and microwave) satellite data have been successfully used to retrieve key land–atmosphere properties, which offers a feasible way to monitor EWEP at different spatiotemporal scales: A decreasing trend of sensible heat flux and an increasing trend of latent heat flux over the TP from 2001 to 2012 were reported. Hourly data of land surface heat fluxes over the entire TP were first obtained, with root mean square errors of 76.6 W m−2 (net radiation flux), 60.3 W m−2 (sensible heat flux), 71.0 W m−2 (latent heat flux) and 37.5 W m−2 (soil heat flux), superior to the previous flux products. The total annual evaporation is approximately 51.7 ± 2.1 km3 year−1 for high-elevation lakes with ice sublimation component accounting for around 10–25%. In addition, different numerical models have been evaluated and improved to study EWEP over heterogeneous land surfaces. The simulation accuracy of land surface temperature and surface energy balance in arid and semiarid areas was improved via an improved heat roughness parameterization scheme in Noah. The sensible heat flux was also effectively improved in the CoLM model by adopting an independent method to determine aerodynamic roughness length. All these results advanced the understanding of different aspects of EWEP over the TP by using in situ measurements, multisource satellite data and numerical modeling. Future studies are recommended to focus on the optimization of the current three-dimensional comprehensive observation system, the development of applicable parameterization schemes and the investigation of EWEP on weather and climate changes over the TP and surrounding regions. [ABSTRACT FROM AUTHOR]

The Himalayas, as a barrier to the monsoonal moisture transport, cause an arid climate on the leeward side. This study investigates the mechanisms of isotopic variations in precipitation on the leeward side of the central Himalayas. Data of Xigaze, which is just north of the central Himalayas, suggest precipitation falls overwhelmingly in the summer monsoon season and subcloud evaporation plays an important role in altering the stable isotopes in precipitation due to the arid climate. Precipitation at Xigaze demonstrates a significant isotopic amount effect, whereby there is a significantly negative correlation between rainfall amount and δ 18 O. Such a result is found to partly arise from the effect of subcloud evaporation, as reflected by increasing evaporative signatures (higher δ 18 O but lower d-excess (d-excess = δD-8δ 18 O)) in rainfall with decreasing rainfall amount. Spatially, a pseud-altitude effect on precipitation δ 18 O and d-excess is observed on the leeward side of the central Himalayas. Lower d-excess but higher δ 18 O in precipitation are found at Xigaze than at Tingri, and this is likely caused by the stronger subcloud evaporation at the lower-altitude site of Xigaze due to its longer descent distance from the cloud base to the ground rather than the rainout process. Additionally, a synoptic survey of streamwaters across the central Himalayas helps to confirm that the spatial variation in isotopic values of precipitation is closely related to the difference in moisture source between windward and leeward sides and the degree of subcloud evaporation on the leeward side. These findings augment our understanding of local- to regional-scale hydroclimate in the central Himalayas. [ABSTRACT FROM AUTHOR]

Tibetan glaciers are natural documents of the specific biomass burning biomarker levoglucosan from regions around. However, knowledge about the characteristics of levoglucosan distributions on Tibetan glaciers under the different climate systems is poorly understood. In this study, we detected levoglucosan in snow samples from the Zuoqiupu (ZQP) Glacier affected by the Indian summer monsoon and the Muji (MJ) Glacier dominated by the westerlies. Results found that the ZQP Glacier was more heavily affected by fire emissions than the MJ Glacier, caused by stronger emission sources on the windward direction and shorter transport distances. Elevations for the appearance of levoglucosan maxima on glacier surfaces are roughly around the equilibrium line altitudes. However, levoglucosan displays a wider distribution range on the MJ glacier than on the ZQP glacier due to weaker summer melt. Injection height of fire smokes and glacial melt can affect the altitudinal distribution of levoglucosan. Black carbon and levoglucosan show different temporal variations in snow-pit samples on those two glaciers. The post-depositional effects, e.g. the melting and refreezing processes, can modulate the vertical distribution of levoglucosan in snow/ice layers. Our results are helpful for understanding the geochemical behaviors of levoglucosan happened on Tibetan glacier surfaces. [ABSTRACT FROM AUTHOR]

Highlights from the article: However, most surge-type glaciers are characteristically long and wide (Barrand and Murray, [1]), while the Aru Glacier is a relatively small glacier with low annual accumulation and slow velocity. Thus, the evidence of glacier sliding might suggest that these glaciers are now in transition from cold base to polythermal due to warming conditions in the region, which thus may threaten the stability of this type of glacier. If the climate warming in the region is the primary cause of the Aru Glacier collapse, then it will not be the last one (the neighboring glacier collapsed on 21 September 2016, with a detached ice area of 6.3 km SP 2 sp and fallen ice volume of ~100 million m SP 3 sp , comparable with the first one).

Constraining temporal and spatial variability in water stable isotopes (δ 18 O and δD) is requested for interpreting proxy records of paleoclimate/paleoaltimetry. The southeastern Tibetan Plateau (TP) receives large amounts of precipitation in both summer (JJAS) and spring (MAM) and this makes it different from most other parts of the TP where annual precipitation concentrates only in summer. However, our knowledge of controls on precipitation and surface runoff generation in this region is still far from sufficient. In this study, the δ 18 O and δD of precipitation and stream waters across the southeastern TP were analyzed to investigate moisture sources and empirical isotope-elevation relationships. Herein, seasonal precipitation patterns, moisture trajectories and precipitation isotopes suggest this region is seasonally dominated by the monsoon in summer and the southerlies (from the Bay of Bengal) or a mix of southerlies and westerlies in spring. Spatially, vertical variations in precipitation seasonality exert profound influences on isotopic variability for stream waters. Larger contributions of spring precipitation (with higher δ 18 O and d-excess (d-excess = δD-8δ 18 O) compared to summer precipitation) vs. summer precipitation in the surface runoff generation at lower elevations account for the uncommon altitudinal decrease in streamwater d-excess. Such a cause also contributes to the slightly greater vertical lapse rates of streamwater δ 18 O (−0.28 to −0.48‰/100 m) relative to the Himalayan front. In addition, although a robust δ 18 O-elevation relationship is demonstrated based upon our measured and other published data on a broad spatial scale (over a 5200 m elevation range), this relationship is found to deviate from the empirical/theoretical pattern in the Himalayan front, which is also caused by the substantial spring precipitation in the southeastern TP. It is suggested that long-term changes in δ 18 O or δD of paleowater in this region actually represent both changes in past regional elevations and contributions of summer vs. spring atmospheric circulations. [ABSTRACT FROM AUTHOR]

This project launched the first study to compare the stable isotopes (δO and δD) in daily precipitation at Kathmandu (located on the southern slope of the central Himalayas) and Tingri (located on the northern slope). The results show that low δO and δD values of summer precipitation at the two stations were closely related to intense convection of the Indian monsoon. However, summer δO and δD values at Tingri were lower than those at Kathmandu, a result of the lift effect of the Himalayas, coupled with convection disturbances and lower temperatures at Tingri. In winter, the relatively high δO and δD values at the two stations appears to have resulted from the influence of the westerlies. Compared with those during the summer, the subsidence of the westerlies and northerly winds resulted in relatively high δO and δD values of the winter precipitation at Tingri. Winter δO and δD values at Kathmandu far exceeded those at Tingri, due to more intense advection of the southern branch of the westerlies, and higher temperatures and relative humidity at Kathmandu. The detailed differences in stable isotopes between the two stations follow short-term variability in the onset date of the Indian monsoon and its retreat across the central Himalayas. During the sampling period, the Indian monsoon onset at Tingri occurred approximately 1 week later than that at Kathmandu. However, the retreat at Tingri began roughly 3 days earlier. Clearly, the duration of the Indian monsoon effects last longer at Kathmandu than that at Tingri. Our findings also indicate that the India monsoon travels slowly northward across the central Himalayas due to the blocking of the Himalayas, but retreats quickly. [ABSTRACT FROM AUTHOR]

Major nuclear bomb tests and nuclear power plant incidents release large amounts of radionuclides. This study investigates beta (β) activities of radionuclides from four ice cores in the Third Pole (TP) to understand the transport routes and related atmospheric processes affecting the radionuclides deposition in glaciers of the region. All the ice cores show three major β activity peaks in the ice layers corresponding to 1963, 1986, and 2011. The β activity peak in the 1963 ice layer is referred to as the well-known 1962 Nuclear Bomb Test. Beta activity peaks in 1986 and 2011 ice layers from the Chernobyl and Fukushima Nuclear Incidents (CNI, FNI). Hysplit forward and backward trajectory analyses suggest that the radionuclides were transported by the westerly into the stratosphere and then to the high elevation TP glaciers. In the FNI case, the radionuclides traveled over Japan, the Pacific Ocean, Europe, and central Asia before being deposited in the TP glaciers. Investigations of the atmospheric circulation confirm that the stronger northern branch of westerly is responsible for high radionuclides during the FNI in the TP. Less precipitation with water vapor flux component divergence after the FNI also contributed to the enriched radionuclides. • We report 3 nuclear events, FNI, CNI, and NBT from β activity peak in TP ice cores. • We found more radionuclides in ice core records after FNI than that after CNI. • Atmosphere transports are responsible for the difference between FNI and CNI. • Strong northern westerly after FNI is responsible for more radionuclides. • Less precipitation and water vapor divergence after FNI led to more radionuclides. [ABSTRACT FROM AUTHOR]

Various types of water samples across the Yarlungzangbo headwater region and its vicinity of the southwestern Tibetan Plateau were collected in summer 2012 for isotopic analysis to augment our specific understanding of regional hydroclimate. In the upper Yarlungzangbo system, contribution of more isotopically depleted tributary influx rather than evaporation is identified as the major hydrological process, and this causes generally progressive depletion in main flow isotopes downstream/eastward. On the regional scale (from the middle Yarlungzangbo basin to the western vicinity of the Yarlungzangbo headwaters), one of the clearest findings is the synchronous increases in river/stream δ18O and d-excess (d-excess= δD - δ18O) from east to west. From a geographical and climatological perspective, these can be explained by increasing contributions of summer-time continental/local recycled vs. monsoonal moisture or winter-spring vs. summer monsoon precipitation in the surface runoff generation westward. The Yarlungzangbo headwaters are at a critical transition between the Indian monsoon system in the east and the westerly one in the west as revealed by the intermediate d-excess and δ18O values, while the Himalaya region farther west (i.e. Pulan region) is predominated by the continental recycled moisture as revealed by the highest d-excess and δ18O values. Furthermore, based upon existing isotopic and meteorological data, a predicted local evaporation line for the Yarlungzangbo headwater region and its vicinity is proposed, which can further help to assess how local hydroclimate affect water stable isotopes. Results of this study provide a baseline for isotopic hydroclimate research in the southwestern Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Based on 20-year (1985-2004) records of surface-air-temperature at 16 stations between the elevations of 3553m and 4801ma.s.l. in the southeastern Tibetan Plateau (or the northern slopes of the eastern Himalayas), this paper examines the monthly, seasonal and annual characteristics of near-surface temperature lapse rates (TLRs). A linear regression model was fitted for the lapse rate calculation. The annual cycle of the TLR shows a distinct seasonal pattern, i.e. steepest in winter and shallowest in summer. Results are partially consistent with those from the southern slopes of the central Himalayas, in particular in summer, and correspond to the warm, rainy and humid season. In response to the monsoonal effect, the released latent heat of water vapour condensation causes an increase in air temperature at higher elevations. Therefore, the TLR is shallowest in the summer. The considerable amount of solar radiation at higher elevations also causes a reduction of the TLR in this season. The lowest diurnal range of lapse rates for summer is associated with lower diurnal variability in net radiation due to cloud cover and relative humidity. The steepest TLR occurs in winter in association with intense cooling at higher elevations, corresponding to the continental dry and cold air surges, and considerable snow-temperature feedback. Lower insolation, deeper snow cover and a weaker inversion effect cause a lower diurnal range of TLR in this season. The observed contrast of winter TLR from the northern to southern slopes of the Himalayas is due to differences in elevation and topography, as well as the pronounced effect of cold air surges. [ABSTRACT FROM AUTHOR]

No glacial lake census exists for the Third Pole region, which includes the Pamir-Hindu Kush-Karakoram-Himalayas and the Tibetan Plateau. Therefore, comprehensive information is lacking about the distribution of and changes in glacial lakes caused by current global warming conditions. In this study, the first glacial lake inventories for the Third Pole were conducted for ~ 1990, 2000, and 2010 using Landsat TM/ETM + data. Glacial lake spatial distributions, corresponding areas and temporal changes were examined. The significant results are as follows. (1) There were 4602, 4981, and 5701 glacial lakes (> 0.003 km 2 ) covering areas of 553.9 ± 90, 581.2 ± 97, and 682.4 ± 110 km 2 in ~ 1990, 2000, and 2010, respectively; these lakes are primarily located in the Brahmaputra (39%), Indus (28%), and Amu Darya (10%) basins. (2) Small lakes (< 0.2 km 2 ) are more sensitive to climate changes. (3) Lakes closer to glaciers and at higher altitudes, particularly those connected to glacier termini, have undergone larger area changes. (4) Glacier-fed lakes are dominant in both quantity and area (> 70%) and exhibit faster expansion trends overall compared to non-glacier-fed lakes. We conclude that glacier meltwater may play a dominant role in the areal expansion of most glacial lakes in the Third Pole. In addition, the patterns of the glacier-fed lakes correspond well with warming temperature trends and negative glacier mass balance patterns. This paper presents an important database of glacial lakes and provides a basis for long-term monitoring and evaluation of outburst flood disasters primarily caused by glacial lakes in the Third Pole. [ABSTRACT FROM AUTHOR]

Investigation of temporal variations in the stable δO and δD isotopes from Kathmandu's precipitation events shows that the relatively enriched δO and δD values in the winter (the dry season, dominated by the westerlies) were positively correlated with temperature, indicating a temperature effect controlling the changes of δO and δD. However, the δO and δD values were depleted in the summer (the wet season, dominated by the Indian monsoon), which were negatively correlated with precipitation amount, indicating an amount effect. In addition, the comparison of stable isotopes in precipitation from Kathmandu and Mawlong (near the Bay of Bengal) shows that the overall trends of δO and δD values at Kathmandu generally approximate those at Mawlong. However, there remain many differences between the details of the isotopic changes at Kathmandu versus those at Mawlong. Compared with those at Mawlong, the further rainout effect and the more intense lift effect of the oceanic moisture by the high mountains resulted in the more depleted δO and δD values in summer precipitation at Kathmandu. A deuterium excess and the local meteoric water lines reveal that evaporation at Kathmandu exceeds that at Mawlong. The data also show that the Indian monsoon activities at Mawlong are more intense than those at Kathmandu. [ABSTRACT FROM AUTHOR]

Fifty-seven snow-bacteria strains were isolated from the snow of the Zadang and Mengdagangri Glaciers located in the central and southern part of the Tibetan Plateau, respectively. 16S rRNA gene sequence analysis showed that strains isolated from the Zadang Glacier belonged to the Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, Firmicutes and Bacteroidetes, and were dominated by the Firmicutes. Strains from the Mengdagangri Glacier belonged to the Actinobacteria, Alphaproteobacteria and Gammaproteobacteria, and were dominated by the Actinobacteria. Sixty-one percent of the isolates were colored with pigment. Sixty-nine percent of isolates from the Zadang Glacier were psychrotolerants, and there were no psychrophiles. We compared the growth-temperature range of 26 snow-bacteria strains to their closest mesophilic type strains and found that 46% of them had an optimum growth-temperature at or lower than 20°C, and 65% were all able to grow at 0°C. However, only 5.3% of mesophilic strains had optimum growth-temperatures at or lower than 20°C, and 9% could grow at 0°C. Snow-bacteria shift their growth-temperature downward; and doing this, in terms of the minimum and optimum temperatures for growth, might be an important strategy for them to adapt to low temperature after they have been deposited on the glacier. Our results suggested that, in order to adapt from mesophilic environments to a cold habitat, snow-bacteria widen their temperature range for growth, convert from mesophiles to psychrotolerants, but not to psychrophiles. In addition, eight isolates formed pigmented colonies, while their mesophilic counterparts were achromogenic. This helped us to confirm through comparative analysis that pigmented microorganisms were more abundant in high-altitude glaciers than in mesophilic environments. [ABSTRACT FROM AUTHOR]

Understanding the changes in number and areal extent of lakes, as well as their abundance and size distribution is important for assessments of regional and global water resources, biogeochemical cycles, and changes in climate. In this study, changes in lake area greater than 1 km are mapped using Landsat datasets, spanning the 1970s, 1990, 2000, and 2010. In addition, high-resolution images (GeoCover Landsat mosaic 2000, with a pixel size of 14.25 m) are used for the first time to map lakes as small as 0.001 km across the entire Tibetan Plateau (TP). Results show that the numbers and areal extent of individual lakes >1 km in size show a slight decrease between the 1970s and 1990, followed by a clear increase from 1990 to 2010. Ninety-nine new lakes are identified between the 1970s and 2010, 71 of which are found between 1990 and 2010. This indicates the accelerated glacier melt and/or increased difference of precipitation minus evaporation since the 1990s. More than 80 % of the lakes show an increase in their area between the 1970s and 2010. The lake census, using 2000 imagery, shows that there are 32,843 lakes with a total area of 43,151.08 ± 411.49 km, which makes up 1.4 % of the total area of the TP. Around 96 % of all lakes are small, with an area <1 km, while the 1,204 large lakes (>1 km) account for 96 % of the total lake area. The TP is subdivided into 12 greater drainage basins, and of these the inner TP dominates in terms of the number of lakes (55.03 %), the total area of lakes (66 %), and lake density (0.026/km compared to the mean, 0.011/km). A plot of lake abundance against size shows that the size distribution of lakes departs from a typical power-law distribution, but displays such a distribution at the mean elevation (4,715 m), with an r value of 0.97 and a slope of −0.66. The slopes of the abundance-size equations from each of the 12 greater basins, and from all basins together, are larger than −1, supporting the inference that larger lakes, rather than the small lakes, contribute more to the total lake surface area across the TP. The lake inventory provided in this study, along with the assessment of lake size distribution, have important implications for estimates of water balance, for water resource management, and for lake area estimations in the TP. [ABSTRACT FROM AUTHOR]