Conference Agenda

Snow depth derived from passive microwave (PMW) with spatial resolution of 25 km is difficult to describe the snow condition and has been generally overestimated in the Qinghai-Tibetan plateau (QTP) which is characterized by patchy snow cover. The main reason for such overestimation is the contribution of low-temperate snow-free ground to the brightness temperature difference between K and Ka bands (TBD). Therefore, in this study, a new method combining MODIS snow cover fraction (SCF) and land surface temperature (LST) and PMW brightness temperature data is developed to derive snow depth at cell size of 0.005^o. MODIS’S SCF is used to identify the snow cover portion of a PMW pixel, and its LST is applied to calculate the TBD contributed from snow-free portion of the PMW pixel. Result shows that after removing such contribution, the TBD value of the PMW pixel is more reasonable and the derived snow depth exhibits relatively smaller errors. The bias and RMSE are 23.4% and 37.3%, respectively, as compared with the 48.5% and 60.5% before such contribution was removed, when using meteorological station observations (2003-2010) as reference. They are 22.5% and 76.1%, respectively, compared with 54.9% and 107.0%, when using field observations (March 2014) as reference. The remaining bias (i.e., overestimation) is mostly due to the TBD contribution (up to 10K) from the low temperature of frozen ground underlying the thin and patchy snow cover (or area). This phenomenon also exists in other cold areas, such as eastern Russia, although not as obvious as on the QTP, because the overall thin and patchy snow cover in QTP could not shield the underling soil from the impact of low air temperature.

Meltwater from rock glaciers could provide a relevant contribution to water supply especially in dry regions. Moreover, rock glaciers could have serious hazard potentials when located at or above steep slopes or when damming lakes. Existing investigations about rock glaciers in High Mountain Asia indicate that the landforms are abundant but information is rare for the Tibetan Plateau and the northern slopes of the Himalaya.

We compiled a rock glacier inventory for the Poiqu region (28° 17´N, 85°58´E) – Central Himalaya/Tibet. The mapping was mainly based on optical images from Sentinel 2 and Google Earth. In addition, we used a hillshade calculated from the new 8 m High Mountain Asia DEM where we filled existing gaps with the 12 m TanDEM-X DEM. Rock glaciers were identified based on their characteristic shape and surface structure. Additional information on the occurrence and activity of the rock glaciers was provided by the InSAR technique using ALOS-1 data.

The preliminary results of the inventory reveal 362 rock glaciers covering an area of about 42 km². The largest one has an area of 2 km² and four have an area of around 1 km². The rock glaciers are located between ~4100 m and ~ 5700 m with a mean altitude of ~5040 m a.s.l.. The mean slope of all rock glaciers is close to 20° (min. 8°, max. 35°). Most of the rock glaciers face towards the Northeast (19%) and West (18.5%). Our study indicates that 158 rock glaciers can be classified as active. We also found rock glaciers damming lakes and infrastructure (streets), which could be threatened by the instability from rock glaciers above.

Future work will concentrate on additional datasets like Sentinel 1 for the improvement of the rock glacier inventory in the Poiqu region.

A group of tongue-shaped periglacial landforms near Jingxian Valley (35°40´N, 94° 00´E) in eastern Kunlun Shan have been reported 20 years ago and classified as “Kunlun-type” rock glaciers due to their unique morphology and slow creeping rates. However, the nature of the northern slopes has remained contentious and later been interpreted as gelifluction deposits. Moreover, the kinematic features of the landform had not been fully investigated or understood. Here, we use satellite SAR interferometry to quantitatively characterize the spatial and temporal changes of the surface movement of these landforms. Five ALOS-1 PALSAR images acquired between 2008 to 2009 over eastern Kunlun Shan area have been used to generate three interferograms to measure the surface movement velocities of the landform. One interferogram records the kinematic information during winter/early spring and the other two are averaged to represent the surface movement during summer. We observe that: (1) the eastern slope is also active with a summer velocity of 20­–60 cm/yr (in the satellite line-of-sight direction, same for all the velocities reported here); (2) the northern lobes moved at 20 to 50 cm/yr in summer, which are much larger than the field measured velocities of less than 3 cm/yr near the front as reported in a previous study conducted from 1980 to 1982; and (3) both the northern lobes and eastern slope are inactive during winter.

The seasonal acceleration in movement of rock glaciers during summer have been observed and, in some cases, no movement can be detected in winter. Gelifluction processes can also trigger seasonal velocity variations. However, creeping rates during summer are typically smaller than 20 cm/yr in cold and dry climate conditions such as Jingxian Valley. Several key pieces of evidence, such as (1) the widespread and relatively fast movement and (2) the large-scale tongue-shaped morphology, suggest that the northern lobes are rockglaciers. The lack of oversteepened fronts presumably results from gelifluction processes of the fine-grained deposits covering the slopes, which smooths out the surface of the landform. The eastern slope shows a similar pattern of seasonal surface kinematic variations to the northern lobes. However, the different morphologic characteristics of the two groups of targets indicate different types of periglacial landforms. With a relatively high surface moving speed and large geometry scale, the northern lobes are unique parts of the alpine permafrost in Eastern Kunlun Shan, representing a mixed type of rock glaciers and gelifluction deposits.

There are approximately 1200 lakes whose area is greater than 1 km² on the Tibetan Plateau (TP), the highest plateau of the world. These lakes are important indicators of environment change because they integrate the basin-wide variations of climate, cryosphere and ecosystems. Previous work on lake changes on the TP during the last several decades have focused on surface area because volume variations need information about lake levels — either in-situ or by satellite altimetry data. However, in-situ measurements are very limited and altimetry data such as ICESat-1 and CryoSat-2 are available at a short term. Here, we present an innovative and robust method that combines digital elevation data and multispectral images to estimate water volume changes for the two largest lakes on the TP, Selin Co and Nam Co from the 1970s to 2015. In addition, the contribution of glacier mass changes to lake volume change between 2000 and 2015 is examined at lake-basin scale using existing estimates based on ICESat and ASTER DEM data. The lake storage changes for Selin Co and Nam Co between 1970s and 2015 are 18.8 and 7.0 Gt. Combining with previous studies of glacier mass balances, the lake volume increase from glacier contribution for two largest lakes, Selin Co and Nam Co, are approximately 28% and 8%, respectively. The future research will extend the estimates of glacier contribution to early 1970s combining declassified satellite data, SRTM and TanDEM-X DTMs and other data sources.

Rock glaciers are important periglacial phenomena in high mountain regions. The Yarlung Tsangpo River basin in the Tibet Autonomous Region of China, the distribution of rock glaciers and their hydrological and environmental effects are poorly understood in the basin. We have produced the first comprehensive inventory of rock glaciers in the Yarlung Tsangpo River basin through the fine spatial resolution satellite data that is freely available on Google Earth, we identified 372 rock glaciers based on their morphological features. We then generated attributes of these rock glaciers including the average length, width, slope, orientation, average elevations of the upper and lower limits, their average elevation and median elevation, as well as hypsometry of each glacier. Through statistical analysis, we show that rock glaciers are situated between 4307 and 5814m a.s.l, with the mean minimum elevation at the front estimated to be 4427 m a.s.l, and the mean maximum elevation at the front estimated to be 5731 m a.s.l. The majority (53%) were found to have a northerly aspect (NE, N, and NW).It provided an important basis for our further understanding of the rock glacier in the Yarlung Tsangpo River basin.

Glacier mass balance, as a direct indicator of climate change, attracted increasing attention in the field of cryosphere. Measuring the region-wide glacier mass balance plays a significant role in understanding the response of glaciers to climate change and their influence on water resources and glacial hazards. In this paper, we derived the mass changes of glaciers according to the geodetic method based on three DEMs representing status of glaciers in different years. These DEMs were generated from declassified Hexagon images (1973-1980), SRTM DEM with 30 m resolution (2000) and TerraSAR-X/TanDEM-X data (2012). All DEMs were co-registered by eliminating errors resulted from horizontal difference and removal of the elevation anomalies. We also took into account errors in the glacier boundary delineation, the seasonal fluctuation in surface elevation, snow and ice density and penetration depth of radar beam. Our expected result is that glaciers mass budgets are negative in the Mt. Xixiabangma during the past period.