We describe volumetric changes in three benchmark glaciers in the Nepal Himalayas on which observations have been made since the 1970s. Compared with the global mean of glacier mass balance, the Himalayan glaciers showed rapid wastage in the 1970s-1990s, but similar wastage in the last decade. In the last decade, a glacier in an arid climate showed negative but suppressed mass balance compared with the period 1970s-1990s, whereas two glaciers in a humid climate showed accelerated wastage. A mass balance model with downscaled gridded datasets depicts the fate of the observed glaciers. We also show a spatially heterogeneous distribution of glacier wastage in the Asian highlands, even under the presentday climate warming.climate change | equilibrium line altitude A recent study (1) has highlighted gross inadequacies both in our knowledge of important changes occurring to Himalayan glaciers and in two recent reports that have alternately overestimated (2) and seriously underestimated (3) the pace of shrinkage of Himalayan glaciers without, in either report (2, 3), offering a compelling basis. However, the rate at which Himalayan glaciers are shrinking remains poorly constrained because ground-based measurements are hampered by the high altitude and remoteness of the region. This lack of observational data has given rise to large uncertainties in both observation-based (4-6) and simulation-based (7-9) projections of global sea-level rise. These studies relied on relationships established for well-studied glaciers under a Euro-American climate. However, this approach may be inaccurate because the seasonal cycle of precipitation has a strong effect on the surface albedo and thus on glacier melt in the monsoonal Asian region (10).In addition, much of the debate on the fate of Himalayan glaciers has missed an important consideration of the height and trend of the equilibrium-line altitude (ELA), which divides the glacier into areas of ablation and accumulation (11). The ELA is important because, for example, if the glacier has no accumulation area for a period because the ELA is located above the glacier, the glacier is destined to disappear over time (12). Unfortunately, observations of the mass balance and ELA of Himalayan glaciers have been made only in recent years (13,14).To address these problems, in the present study we update the elevation data for Himalayan benchmark glaciers, providing information for the past decades. We calculate changes in the mass balance and ELA of the three benchmark glaciers using an energy-mass balance model with downscaled gridded climate datasets, in order to describe the state and fate of glaciers. Further calculations are performed to assess the spatial representativeness of the observation-based results.

Due to remoteness and high altitude, only a few ground-based glacier change studies are available in high-mountain areas in the Himalaya. However, digital elevation models based on remotely sensed data (RS-DEMs) provide feasible opportunities to evaluate how fast Himalayan glaciers are changing. Here we compute elevation changes in glacier surface (total area 183.3 km2) in the Khumbu region, Nepal Himalaya, for the period 1992-2008 using multitemporal RS-DEMs and a map-derived DEM calibrated with differential GPS survey data in 2007. Elevation change is calculated by generating a weighted least-squares linear regression model. Our method enables us to provide the distribution of uncertainty of the elevation change. Debris-covered areas show large lowering rates. The spatial distribution of elevation change shows that the different wastage features of the debris-covered glaciers depend on their scale, slope and the existence of glacial lakes. The elevation changes of glaciers in the eastern Khumbu region are in line with previous studies. The regional average mass balance of -0.40 ± 0.25 m w.e.a-1 for the period 1992-2008 is consistent with a global value of about -0.55 m w.e. a-1 for the period 1996-2005.

We present a new glacier inventory for highmountain Asia named "Glacier Area Mapping for Discharge from the Asian Mountains" (GAMDAM). Glacier outlines were delineated manually using 356 Landsat ETM+ scenes in 226 path-row sets from the period 1999-2003, in conjunction with a digital elevation model (DEM) and highresolution Google Earth TM imagery. Geolocations are largely consistent between the Landsat imagery and DEM due to systematic radiometric and geometric corrections made by the United States Geological Survey. We performed repeated delineation tests and peer review of glacier outlines in order to maintain the consistency and quality of the inventory. Our GAMDAM glacier inventory (GGI) includes 87 084 glaciers covering a total area of 91 263 ± 13 689 km 2 throughout high-mountain Asia. In the Hindu Kush-Himalaya range, the total glacier area in our inventory is 93 % that of the ICIMOD (International Centre for Integrated Mountain Development) inventory. Discrepancies between the two regional data sets are due mainly to the effects of glacier shading. In contrast, our inventory represents significantly less surface area (−24 %) than the recent global Randolph Glacier Inventory, version 4.0 (RGI), which includes 119 863 ± 9201 km 2 for the entirety of high Asian mountains. Likely causes of this disparity include headwall definition, effects of exclusion of shaded glacier areas, glacier recession since the 1970s, and inclusion of seasonal snow cover in the source data of the RGI, although it is difficult to evaluate such effects quantitatively. Further rigorous peer review of GGI will both improve the quality of glacier inventory in high-mountain Asia and provide new opportunities to study Asian glaciers.

ABSTRACT. Debris cover is widely present in glacier ablation areas of the Tibetan Plateau, and its spatial distribution greatly affects glacier melt rates. High-resolution in situ measurements of debris thickness on Hailuogou glacier, Mount Gongga, southeastern Tibetan Plateau, show pronounced inhomogeneous debris distribution. An analysis of transverse and longitudinal profiles indicates that the ground-surveyed debris thicknesses and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)-derived thermal resistances of debris layers correlate strongly over the entire ablation area. Across-and along-glacier patterns of ASTER-derived thermal resistance correspond well with spatial patterns of debris thickness, which may reflect large-scale variations in the extent and thickness of the debris cover. The ice melt rate variability over the ablation area simulated by a surface energy-balance model that considered thermal resistance of the debris layer indicates clearly the crucial role of debris and its spatial continuity in modifying the spatial characteristics of melt rates. Because of the inhomogeneous distribution of debris thickness, about 67% of the ablation area on Hailuogou glacier has undergone accelerated melting, whereas about 19% of the ablation area has experienced inhibited melting, and the sub-debris melt rate equals the bare-ice melt rate in only 14% of the ablation area.