The Himalaya, the world's highest mountain ranges, are home to a large group of glaciers and glacial lakes. Glacial lake outburst floods (GLOFs) in this region have resulted in catastrophic damages ...and fatalities in the past decades. The recent warming has caused dramatic glacial lake changes and increased potential GLOF risk in the Himalaya. However, our knowledge on the current state and change of glacial lakes in the entire Himalaya is limited. This study maps the current (2015) distribution of glacial lakes across the entire Himalaya and monitors the spatially-explicit evolution of glacial lakes over five time periods from 1990 to 2015 using a total of 348 Landsat images at 30m resolution. The results show that 4950 glacial lakes in 2015 cover a total area of 455.3±72.7km2, mainly located between 4000m and 5700m above sea level. Himalayan glacial lakes expanded by approximately 14.1% from 1990 to 2015. The changing patterns of supraglacial lakes and proglacial lakes are rather complex, involving both lake disappearance and emergence. Many emergent glacial lakes are found at higher elevations, especially the new proglacial lakes, which have formed as a result of glacier retreat. Spatially heterogeneous changes of Himalayan glacial lakes are observed, with the most significant expansion occurring in the southern slopes of the central Himalaya. Increasing glacier meltwater induced by the Himalayan atmospheric warming is a primary cause for the observed lake expansion. This study provides primary data for future GLOF risk assessments. A total of 118 rapidly expanded glacial lakes are identified as potential vulnerable lakes for the priority of risk assessment.
•Revealing the distribution of Himalayan glacial lakes using Landsat 8 images in 2015•Demonstrating the evolution and regional heterogeneity of Himalayan glacial lakes•Detecting the rapidly expanding glacial lakes with potential outburst risk
Glacial lake outburst flood (GLOF) is a serious hazard in high, mountainous regions. In the Himalayas, catastrophic risks of GLOFs have increased in recent years because most Himalayan glaciers have ...experienced remarkable downwasting under a warming climate. However, current knowledge about the distribution and recent changes in glacial lakes within the central Himalaya mountain range is still limited. Here, we conducted a systematic investigation of the glacial lakes within the entire central Himalaya range by using an object-oriented image processing method based on the Landsat Thematic Mapper (TM) or Enhanced Thematic Mapper (ETM) images from 1990 to 2010. We extracted the lake boundaries for four time points (1990, 2000, 2005 and 2010) and used a time series inspection method combined with a consistent spatial resolution of Landsat images that consistently revealed lake expansion. Our results show that the glacial lakes expanded rapidly by 17.11% from 1990 to 2010. The pre-existing, larger glacial lakes, rather than the newly formed lakes, contributed most to the areal expansion. The greatest expansions occurred at the altitudinal zones between 4800 m and 5600 m at the north side of the main Himalayan range and between 4500 m and 5600 m at the south side, respectively. Based on the expansion rate, area and type of glacial lakes, we identified 67 rapidly expanding glacial lakes in the central Himalayan region that need to be closely monitored in the future. The warming and increasing amounts of light-absorbing constituents of snow and ice could have accelerated the melting that directly affected the glacial lake expansion. Across the main central Himalayas, glacial lakes at the north side show more remarkable expansion than those at the south side. An effective monitoring and warning system for critical glacial lakes is urgently needed.
Glacial lake outburst floods (GLOFs) are a unique type of natural hazard in the cryosphere that may result in catastrophic fatalities and damages. The Himalayas are known as one of the world's most ...GLOF-vulnerable zones. Effective hazard assessments and risk management require a thorough inventory of historical GLOF events across the Himalayas, which is hitherto absent. Existing studies imply that numerous historical GLOF events are contentious because of discrepant geographic coordinates, names, or outburst time, requiring further verifications. This study reviews and verifies over 60 historical GLOF events across the Himalayas using a comprehensive method that combines literature documentations, archival remote sensing observations, geomorphological analysis, and field investigations. As a result, three unreported GLOF events were discovered from remote sensing images and geomorphological analysis. Eleven suspicious events were identified and suggested to be excluded. The properties of five outburst lakes, i.e., Degaco, Chongbaxia Tsho, Geiqu, Lemthang Tsho, and a lake on Tshojo Glacier, were corrected or updated. A total of 51 GLOF events were verified to be convincing, and these outburst lakes were classified into three categories according to their statuses in the past decades, namely disappeared (12), stable (30), and expanding (9). Statistics of the verified GLOF events show that GLOF tended to occur between April and October in the Himalayas. We suggest that more attention should be paid to rapidly expanding glacial lakes with high possibility of repetitive outbursts. This study also demonstrates the effectiveness of integrating remote sensing and geomorphic interpretations in identifying and verifying GLOF events in remote alpine environments. This inventory of GLOFs with a range of critical attributes (e.g., locations, time, and mechanisms) will benefit the continuous monitoring and prediction of potentially dangerous glacial lakes and contribute to outburst-induced risk assessments and hazard mitigations.
•Developed a comprehensive method to review and verify historical GLOF events•Verified the persuadability for over 60 Himalayan GLOF events•Revealed the statuses of Himalayan outburst lakes in the past decades•Constructed a GLOF inventory with many critical attributes for hazard assessments
•Periodic accelerations of a lake-terminating glacier are linked to rapid frontal retreats.•Proglacial lake-ice interactions can greatly modify the ice flow regime.•Recent terminus acceleration has ...likely induced glacier upstream dynamic thinning.•In contrast, a neighboring land-terminating glacier shows on-going deceleration.
Most lake-terminating glaciers in the Himalaya retreat rapidly due to periodic frontal ice loss at their terminus, but long-term observations are still limited regarding their flow dynamics, which is crucial for understanding the processes of ice mass loss and proglacial lake growth. We present multi-decadal surface velocity dynamics of the Longbasaba Glacier, a rapid retreating lake-terminating glacier in the Chinese Himalaya, using an image feature tracking method applied on optical satellite images between 1989 and 2018. We show that, in companion with rapid retreat (−51.7 m a−1), its lower 5 km tongue experienced high interannual fluctuations in velocity, comprising periodic acceleration and slowdown in 1989-1995 and 2001-2010 and a recent remarkable acceleration since 2012. The temporal variation of longitudinal velocity distribution indicates an upward propagation of the lake-ward acceleration (namely a downglacier inversion of strain from compression to extension). This propagation is coupled to the retreat of the glacier front and occurs along the lowermost 1∼1.5 km lake-adjacent section as the proglacial lake expands. The most recent acceleration of the near-lake section since 2012 has likely facilitated a dynamic thinning on its upper sections, where flow acceleration started two years later in 2014. This pattern contrasts markedly with a nearby decelerating land-terminating glacier, which has experienced a much slower retreat rate (−7.8 m a−1) and the same magnitude of mean thinning rate at its lower part since 2000. Our results confirm the strong influence of the proglacial lake on ice flow dynamics and suggest that lake-ice interactions are important to consider when analyzing, interpreting or modeling dynamics of rapidly retreating lake-terminating glaciers in the Himalayas as well as around the world.
The meltwater released by the glaciers in the Aksu-Tarim Catchment, south of Tomur Peak (Central Tien Shan), feeds the Tarim River which is the main artery for the oases at the northern margin of the ...Taklamakan desert. The correct modeling of the contribution of the glaciers meltwater to the total runoff of the Tarim River is hampered by the lack of mass balance data. Multi-temporal digital terrain models (DTMs) allow the determination of volume changes for large samples of glacier. Here, we present the mass changes for 12 glaciers using 1976 KH-9 Hexagon, 2000 SRTM3 and 2009 SPOT-5 datasets. The results show that most of the glaciers have been losing mass since 1976. The largest glaciers, Koxkar and West Qongterang, lost −0.27±0.15mw.e.a−1 and −0.43±0.15mw.e.a−1 between 1976 and 2009, despite thick debris cover. However, some smaller glaciers show mass gain at their tongues indicating glacier surges. Using SRTM3 data the volume gain of Qinbingtan Glacier No. 74 could be dated to the time period 1999–2009. The overall mass budget of −0.33±0.15mw.e.a−1 (for 1976–2009) of the investigated glaciers is within the variability range of the global average. However, in the recent years (1999–2009) a slightly decelerated mass loss of −0.23±0.19mw.e.a−1 could be observed.
► We generate DTMs based on spaceborne (KH-9 Hexagon and SPOT-5) imagery. ► Mass balances are calculated for glaciers south of Tomur Peak. ► An overall mass budget of −0.33±0.15mw.e.a−1 (1976–2009) is determined. ► Mass gains are found for smaller glaciers. ► In the recent years (1999–2009) a slightly decelerated mass loss (−0.23±0.19mw.e.a−1) is observed.
High-resolution, long-term and accurate daily-precipitation is always difficult and rarely measured in the Qinghai-Tibet Plateau (QTP) because of the high altitude and complex terrain. The accuracy ...of satellite-based gridded precipitation products have been continuously improved recently which is crucial to the study of cryosphere ecology and environment. The goal of this study is to evaluate the accuracy of CHIRPS v2 (Climate Hazards Group Infrared Precipitation with Stations data, version 2) and MSWEP v2 (Multi-source weighted-Ensemble Precipitation, version 2) daily-precipitation products over the QTP during the period 1981–2015. Validation was done using a time series of daily-precipitation data obtained from 104 hydrometeorological stations distributed over the QTP. Error metrics (The correlation coefficient CC, the relative bias BIAS, and root mean square error RMSE) were used for accuracy evaluation and detectability indicators (probability of detection POD, false alarm ratio RFA, and critical success index CSI) were used for the analysis of detection capabilities of rainfall occurrence events. The results indicate that when compared to rain gauge observations, CHIRPS and MSWEP daily-precipitation products represent well the spatial and temporal distribution of the mean daily precipitation over the QTP, while both of them overestimate the daily-precipitation (0.18 mm/d for CHIRPS, 0.56 mm/d for MSWEP). MSWEP performed better than CHIRPS according to CC (MSWEP is 0.44, CHIRPS is 0.23) and RMSE (MSWEP is 4.21 mm, CHIRPS is 5.03 mm) and MSWEP showed better detection capabilities with higher POD (0.65), lower RFA (0.50) and higher CSI (0.39) in the QTP. Both products are less accurate in dry conditions (the north QTP, winter) than in moist conditions (the south QTP, summer). Light precipitation events (0–2 mm/d) are underestimated but heavy precipitation events (2–25 mm/d) are overestimated. CHIRPS and MSWEP have shown great potential to be able to be applied to the precipitation-related study of the QTP. Although the accuracy of MSWEP is higher than that of CHIRPS, the latter has higher spatial resolution (o.o5°) and is more suitable for small-scale studies.
•The evaluation results indicate that the newly released MSWEP perform better than CHIRSP in daily scale from 1981 to 2015.•Both two products indicate that drought conditions (the north QTP, winter) are less accurate than rainfall conditions (the south QTP, summer).
A study is presented of the geographical distribution and spatial and temporal variabilities of the western China snow cover in the past 47 yr between 1951 and 1997. The data used consist of Scanning ...Multichannel Microwave Radiometer (SMMR) 6-day snow-depth charts, NOAA weekly snow extent charts, and the daily snow depth and number of snow cover days from 106 selected meteorological stations across western China. Empirical orthogonal function was performed on the SMMR dataset to better understand the spatial pattern and variability of the Qinghai–Xizang (Tibet) snow cover. A multiple linear regression analysis was conducted to show the association of interannual variations between snow cover and snow season temperature as well as precipitation. Further, the autoregressive moving average model was fitted to the snow and climate time series to test for their long-term trends. Results show that western China did not experience a continual decrease in snow cover during the great warming period of the 1980s and 1990s. It is of interest to note that no correlation was identified between temperature and precipitation in the snow cover season. However, year-to-year fluctuation of snow cover responds to both snowfall and snow season temperature. About one-half to two-thirds of the total variance in snow cover is explained by the linear variations of snowfall and snow season temperature. The long-term variability of western China snow cover is characterized by a large interannual variation superimposed on a small increase trend. The positive trend of the western China snow cover is consistent with increasing snowfall, but is in contradiction to regional warming. In addition, many constraints of the Qinghai–Xizang (Tibet) snow cover force the author’s challenge of Blanford’s hypothesis.
Physical erosion and chemical weathering rates beneath glaciers are expected to increase in a warming climate with enhanced melting but are poorly constrained. We present a global dataset of cations ...in meltwaters of 77 glaciers, including new data from 19 Asian glaciers. Our study shows that contemporary cation denudation rates (CDRs) beneath glaciers (2174 ± 977 Σ*meq
m
year
) are ~3 times higher than two decades ago, up to 10 times higher than ice sheet catchments (~150-2000 Σ*meq
m
year
), up to 50 times higher than whole ice sheet means (~30-45 Σ*meq
m
year
) and ~4 times higher than major non-glacial riverine means (~500 Σ*meq
m
year
). Glacial CDRs are positively correlated with air temperature, suggesting glacial chemical weathering yields are likely to increase in future. Our findings highlight that chemical weathering beneath glaciers is more intense than many other terrestrial systems and may become increasingly important for regional biogeochemical cycles.
In the Tibetan Plateau, many glaciers have extensive covers of supraglacial debris in their ablation zones, which affects glacier response to climate change by altering ice melting and spatial ...patterns of mass loss. Insufficient debris thickness data make it difficult to analyze regional debris-cover effects. Maritime glaciers of the Mount Gongga have been characterized by a substantial reduction in glacier area and ice mass in recent decades. The thermal property of the debris layer estimated from remotely sensed data reveals that debris-covered glaciers are dominant in this region, on which the proportion of debris cover to total glacier area varies from 1.74% to 53.0%. Using a physically-based debris-cover effect assessment model, we found that although the presence of supraglacial debris has a significant insulating effect on heavily debris-covered glaciers, il accelerates ice melting on -10.2% of total ablation zone and produces rapid wastage of -25% of the debris-covered glaciers, leading to the similar mass losses between the debris-covered and debris-free glaciers. Widespread debris cover also facilitates the development of active terminus regions. Regional differences in debris-cover effects are apparent, highlighting the im- portance of debris cover for understanding glacier mass changes in the Tibetan Plateau and other mountain ranges around the world.
As a climate-sensitive region, the glacier on Qilian Mountain is changing rapidly, and climate change can rapidly increase glacier flow instabilities through movement and ablation. We used the ...thermo-mechanically-coupled-with-full-Stokes code with the Elmer method to perform a steady-state diagnostic simulation of the Shuiguan River Glacier No. 3 (SG3) in the eastern Qilian Mountains, and to predict and analyze future changes of the glacier in combination with historical elevation data. The results showed that the average ice temperature was above −1.5 °C, that the hydrological process inside and under the ice was complex, and that the high ice temperature at the bottom would make the glacier fragile in the future. Because of the small thickness of the glacier and the small stress in the ice, the stress of the ice flow caused no great damage to the glacier. The development of cracks and melting holes under the ice was mainly caused by the melting of the glacier. Prognostic simulation under two climate models (RCP 4.5 and RCP 8.5) revealed that the area of SG3 changed evenly at first, and then retreated at an accelerated rate, whereas the volume consistently presented a state of accelerated reduction. Although our study confirmed that climatic warming was the main reason for glacial retreat, it was also found that the altitude of the glacier, the topography of the bedrock under the ice and the accumulation area would greatly affect the response of the glacier to climatic change. For these reasons, our study also profoundly elucidated why different glaciers with the same scale and under the same climatic conditions could exhibit different changes in area and terminal position.
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•A thermo-mechanically-coupled model was used to detect glacier dynamics.•Ice velocity, ice temperature and stress were simulated.•The small accumulated area is the reason for the rapid retreat of glaciers.•The glacial altitude zone and bedrock topography greatly affect shrinkage rates.•The destructive effect on the smaller glaciers mainly comes from ablation.
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