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We evaluated elevation changes at four sites on debris-covered ablation area of Khumbu Glacier, Nepal Himalaya, since 1978. In 2004, we carried out a ground survey by differential GPS in the upper- and lowermost areas of the ablation area. The amount of surface lowering was calculated by comparing digital elevation models (DEMs) with 30-m grid size, as generated from survey data corrected in 1978, 1995, and in the present study. Because we could not access the middle parts of the debris-covered area due to surface roughness, for this area we used an ASTER-DEM calibrated by the ground survey data. The amount of surface lowering during the period 1978–2004 was insignificant near the terminus. A remarkable acceleration of surface lowering was found in the middle part of the debris-covered ablation area, where the glacier surface is highly undulating. In the uppermost area, surface lowering has continued at a steady rate. Surface flow speeds have decreased since 1956, revealing that the recent decrea...

The mass balance of the Xiao (Lesser) Dongkemadi Glacier located in the Tanggula Mountains, of the central Qinghai-Tibetan Plateau has been monitored since 1989. The results show that the mass balance of the glacier has recently shown a deficit trend, and that the glacial terminus was also retreating. Positive mass balance of the glacier was dominant during the period 1989–1993, and the accumulated mass balance reached 970 mm. However, negative mass balance of the glacier has occurred since 1994, except for the large positive mass balance year 1997. The mass balance was − 701 mm in 1998, an extremely negative glacier mass balance year. The equilibrium line altitude showed a significant increasing trend. The mass balance of the glacier has changed from a significantly positive mass balance to a strongly negative mass balance since 1994. Meteorological data suggest that the rapid decrease in the mass balance is related to summer season warming. Copyright © 2007 John Wiley & Sons, Ltd.

Model calculations are made in order to understand the characteristics and response to climate change of runoff from a cold glacier on the Tibetan Plateau. Some 20% of meltwater is preserved at the snow–ice boundary due to refreezing, since the glaciers in mid to northern Tibet are sufficiently cooled during the previous winter. Sensitivity to alterations in meteorological parameters has revealed that a change in air temperature would cause not only an increase in melting by sensible heat, but also a drastic increase in melting due to lowering of the albedo, since some of the snowfall changes to rainfall. In addition, it was suggested that a decrease in precipitation would cause a lowering of the surface albedo, with a resulting increase in the contribution of glacier runoff to the total runoff of river water. This study shows the first quantitative evaluation of the above effects, though they have been suggested qualitatively. The seasonal sensitivity of glacier runoff was examined by changing the dates given for a meteorological perturbation for a period of only 5 days. It was revealed that changes in both air temperature and precipitation during the melting season strongly affected glacier runoff by changing the surface albedo, though these perturbations only slightly altered the annual averages. Copyright © 2006 John Wiley & Sons, Ltd.

Though solar radiation is important for glacier mass-balance simulation, solar radiation data are not always available. As a result of analyzing meteorological data measured in the Himalaya and the Tibetan Plateau, a favorable correlation between precipitation and atmospheric transmissivity of solar radiation is found in terms of monthly values. Monthly mean solar radiation is derived from the relationship between atmospheric transmissivity of solar radiation and precipitation with input of monthly precipitation, latitude, skyline and time. The differences between estimated and observed monthly mean solar radiation are −2 in most cases. However, the differences at some sites are significantly large. The error in the estimated solar radiation during the monsoon season can be large when the monthly mean precipitation rate is about 5 mm d−1. Though the error in the estimated solar radiation during the non-monsoon season is generally small due to low precipitation in the Himalaya and the Tibetan Plateau during this season, it can exceed 100 W m−2.

Data on the mass balance of Xiao Dongkemadi glacier in the Tanggula mountains, central Tibetan Plateau, were obtained over 5 5 years from 1989 to 1995. These are the first continuous mass-balance data for a continental-type glacier on the Tibetan Plateau, where the glacier accumulates during the summer monsoon (summer-accumulation-type glacier). Mass-balance vs altitude profiles were steeper in the negative than in the positive mass-balance years. This is considered to have resulted from the effect of summer accumulation. The annual mass balance is compared with air temperature, precipitation, and black-body temperature in the area including the glacier, which is calculated from infrared radiation observations by theJapanese Geostationary Meteorological Satellite. It was found that the interannual variation in the glacier mass balance was not closely related to maximum monthly mean air temperature, while it did have a relatively good correlation with maximum monthly mean black-body temperature.

A mass-balance model based on the energy balance at the snow or ice surface is formulated, with particular attention paid to processes affecting absorption of radiation. The model is applied to a small glacier, Glacier AX010 in the Nepalese Himalaya, and tests of its mass-balance sensitivity to input and climatic parameters are carried out. Calculated and observed area-averaged mass balances of the glacier during summer 1978 (June-September) show good agreement, namely -0.44 and -0.46 m w.e., respectively.Results show the mass balance is strongly sensitive to snow or ice albedo, to the effects of screening by surrounding mountain walls, to areal variations in multiple reflection between clouds and the glacier surface, and to thin snow covers which alter the surface albedo. In tests of the sensitivity of the mass balance to seasonal values of climatic parameters, the mass balance is found to be strongly sensitive to summer air temperature and precipitation but only weakly sensitive to relative humidity.

In the Himalayas-Tibet, glaciers varied much due to uplift of the area and variation of the monsoon as well as general climatic change since Quaternary ice ages. The variation of glacier mass balance is described qualitatively on the basis of present characteristics of summer-accumulation type glaciers. Variation of such glaciers is sensitive to that of summer temperature. Transition of annual variation patterns of the glacier mass balance is shown for the period from the last ice age to the present. Increase of ablation due to decrease of the surface albedo is considered to be effective in shrinking of the glaciers during this period. It is pointed out that development of methods to reconstruct the paleo-water-cycle under changing influence of the monsoon is important to clarify the history of areal characteristics of glacier accumulation.

In 1978, the first detailed glaciological studies were carried out on the small glacier AX010 in a glacier inventory of Dudh Kosi region, in the Nepal Himalaya. Its length, area and highest and lowest elevations in 1978 were 1.7 km, 0.57 km2, 5360 and 4950 m a.s.l., respectively. Two resurveys of its terminus position and/or surface elevations were carried out in 1989 and 1991. The glacier retreated by about 30 and 28 m during the periods 1978–89 and 1989–91, respectively. In 1995, annual monitoring of this glacier by means of ground survey, stake method and topographical mapping began, in order to obtain its mass balance, surface flow velocity and extent, and link them with climatic conditions. The results obtained in 1995 are summarized as follows: (1) During the period 1991–95, the glacier retreated by 12 m. (2) Associated with the ice-thickness loss in the lower part of the glacier, the horizontal surface velocities along the center line in 1995 (June–October) showed a remarkable decrease on the glacier tongue, to about 50% of those in 1978. Shrinkage of the glacier in the near future is predicted from a simple model calculation for the case that climatic conditions remain unchanged from 1995. The results show that the present shrinkage should continue and accelerate.

The relations between mass balance and meltwater refreezing were examined on the basis of glaciological observations carried out in summer 1993 on Xiao Dongkemadi Glacier, Tanggula Mountains, central Tibetan Plateau. On this glacier, a part of meltwaler refreezes at the snow/ice interface as superimposed ice. The amount of superimposed ice formation was determined by both meltwater supply and temperature condition of the glacier. Snow-layer thickness on the glacier ice body is less than 2 m, even in the higher accumulation zone. About 60% of meltwaler generated in the accumulation zone for the period May–September was trapped at the snow/ice interface by refreezing, and was not discharged out of the glacier. About 26% of accumulated snow to the glacier surface was replaced on the snow/ice interface by refreezing in the accumulation zone. These facts indicate that superimposed ice formation is quite significant for water retention in glaciers under low-precipitation conditions.

アジアでは比較的情報の多い中国西部と旧ソ連の氷河変動資料をまとめた.1960年代から80年代初期にかけて,コンロン山域以外は後退氷河が多く,アルタイ,天山,パミール,チーレン山域の順に北方ほどその傾向が強い.しかし,この間に中国西部やパミールでは1960-70年代に後退から前進に転じる氷河が増え,一方,旧ソ連天山やコーカサスでは後退傾向が優勢なまま,大きな変化はない.また,約30年＆sim;60年間程度の氷河変動データのある乾燥域(大陸性)の3氷河(2＆sim;4km長)と湿潤域(海洋性)の3氷河(10＆sim;13km長)について,年間末端変動距離の氷河長に対する割合の年による変化をみた.1980年代はいずれの氷河も5m/km程度までの後退範囲にあったが,毎年観測されているTs.Tyuksu氷河(西部天山)とウルムチ1号氷河(東部天山)では,この間に後退量が増えつつある.この2氷河について,氷河変動と夏気温や年降水量との関係を紹介した.

[1] We describe four decades of temporal fluctuations in the ablation of the Hamaguri-yuki snow patch in the northern Japan Alps. Annual ablation depth through the melting season shows a significant correlation with the initial depth (at the beginning of the melting season), whereas a less significant correlation is found with a temperature index that is generally believed to correlate well with ablation. The scale effect of the snow patch, which appears to modify the wind speed over the patch, has a more significant effect on snow ablation than does the radiation shadowing effect of surrounding mountains. In the case of a thinner and therefore smaller initial springtime snow patch, the speed of the local wind may be reduced over the snow surface, thereby suppressing ablation, whereas wind speed is not reduced (and ablation is not suppressed) in the case of a thicker snow patch. This self-regulating feedback means that over the past four decades, the thickness of the snow patch has fluctuated in a manner that is largely independent of summertime temperature. Our findings also suggest that the self-regulating feedback, which influences ablation, allows some small wind-drifted glaciers to survive, whereas previous studies reported enhanced accumulation at such glaciers via a similar topographic effect on wind speed and suppressed ablation via the shading effect of surrounding mountains on solar radiation.

Annual mass exchange differs between maritime and continental glaciers. A common characteristic of these glaciers in Asian high-mountain areas is that most of the annual accumulation occurs in summer. Since variations in mass balance of a summer-accumulation type of glacier are quite sensitive to variations in summer air temperature, shrinkages of such glaciers due to climate warming are predicted by the use of simplified experimental relations between air temperature and mass balance, disregarding variation of other climatic variables such as cloudiness and precipitation. The results predict that both small and large maritime glaciers are more sensitive to warming than a continental ice cap. A small glacier would disappear in a few decades if the air temperature persisted a few degrees above that of an equilibrium state of mass balance.

[1] Two net balance records of neighboring glaciers under different conditions are analyzed to extract temporal variations in glacier melting in the Himalayas. Significant melt was observed every year at one site (wet site), whereas no melt occurred at the second site because of its high elevation (dry site). Accumulation at the wet site of a glacier is estimated from the dry site neighboring another glacier through a measured precipitation record for a short time period. The difference between the estimated accumulation and the net balances at the wet site is obtained as the “melt index,” which represents the glacier melting conditions. The melt index with an interannual timescale is significant as a climatic proxy at high elevation since no relationship between stable isotopes and temperature is established and few long-term temperature records are available at high elevations in the Himalayas. The melt index showed a decadal fluctuation with a major amplitude never reported in previous studies with respect to temperature and ice cores analyses in the Himalayas. Ice cores from a site where significant melt occurs every year have not been considered available in reconstructing past climates since climatic signals in ice were disturbed by meltwater infiltration. However, we suggest a new approach to glean temperature information by a combination of wet and dry cores, not obtainable from a good-quality ice core alone.

Glacier fluctuations during the Holocene in the Himalayas are compared with those in the world. Characteristics of glacier mass balance in the Nepal Himalaya, which belongs to the summer-accumulation type, are described. And the glacier fluctuations after the Little Ice Age in the Nepal Himalaya are discussed on the basis of variation of summer air temperature, which is the controling factor of glacier mass balance in this area.

A thermal drilling was carried cut in August of 1974 on the Khumbu Glacier flowing from Mt. Sagarmatha (English name Everest) in the East Nepal Himalayas. The drilling site was set at 5, 360 m above sea-level in the upper part of the ablation area of the glacier.The drilling was continued to a depth of 20.3 m where the drilling stopped due to the freezing of the drilled hole. Down to the depth, the relationship between the depth and the time of drilling was obtained, and the analysis of the results obtained showed that there were 7 layers down to a depth of 20 m. Three layers of them were ordinary glacier ice layers, three layers were blue ice layers or ice layers contaminated with dirt, and one layer corresponded to a vertically distributed ice layer containing air bubbles or a horizontally distributed ice layer containing water.A simple calculation of the freezing rate of the drilled hole showed that the ice temperature at a depth of 2 m was below -2°C at the time of drilling. The measurement of the resistance of a thermister put into the hole showed the ice temperature at a depth of 2.7 m was -5.3°C on 23rd November. Therefore, it was concluded that the distribution of ice temperature in the ablation area of the glacier might be of the polar type.

Observations of water discharge from a drainage area of 142.5 km2 including glacier zones were made at Dingboche (4330 m) in east Nepal. The annual discharge of this drainage was estimated as 1.7 × 108m3. The annual variation of the discharge showed a tendency to increase in summer and decrease in winter. It is assumed that precipitation during the monsoon season strongly contributes to high discharge in summer. On the basis of the data of ablation of glaciers and precipitation in this region, preliminary estimates of water balance in the drainage during a year were made. Since the variation of daily mean air temperature at Lhajung near Dingboche had a good correlation with the vatiation of daily discharge in summer but not in winter, the contribution of melt water from glaciers to the variation of the discharge was also discussed on the basis of the air temperature over glaciers estimated from the monthly mean temperature at Lhajung. Diurnal variations of the discharge in different months showed periodic tendencies which might be due to the diurnal variations of discharge of melt water from glaciers. The seasonal change of this tendency can be explained by the change of air temperature. Monthly discharge in depth of runoff from this drainage was compared with that at a point 460 m in altitude, in the lower part of this drainage. The latter was nearly twice as much as the former during the monsoon season, since precipitation in the upper drainage during the monsson season is less than below.

Observation of mass balance of Glacier AX010 at the southern front of the Nepal Himalayas was made from June to September in 1978. Since much of the annual accumulation due to the monsoon. and ablation occur simultaneously in the summer, the separate measurement of the amounts of accu mulation and ablation is difficult in this area. Accumulation is estimated from the precipitation on the basis of the relation between the probability of occurrences of solid precipitation ana surface air temperature, and ablation is obtained from the difference between the accumulation and the observational results of the balance. The probability of occurrences of solid precipitation had different linear relations with the air temperature between daytime and nighttime. The relation of air temperature to the estimated ablation is expressed by a power function. Although the change of accumulation depended on air temperature, the ablation was much more sensitive to the change of air temperature. The average summer balance over the whole area of the glacier was negative, but the positive summer balance in recent years is deduced. It is concluded that the fluctuation of the summer temperature on glaciers in the Nepal Himalayas under the influence of the summer monsoon is important for the variation of mass balance.

Glaciological observations were made for the study of the glacier mass balance in the Nepal Himalayas, which is characterized by the simultaneous occurrence of considerable accumulation and ablation during the summer monsoon season. The upward change of the glacier surface level and the considerable amount of deposited snow due to the summer snowfall were observed at the end of summer over the whole area of the glaciers by means of stake measurements and stratigraphic observations respectively. On the other hand, the mass balance from July to September is calculated in consideration of the ice amount to be superimposed on the glacier ice of sub-zero temperature. The growth of the superimposed ice contributed to the positive mass balance in the upper-middle part of the glacier, while the mass balance during the same period was negative in the lower part. The total of the sum mer balance for the whole area of each observed glacier is concluded to have been positive. Such a positive summer balance is attributed mainly to the accumulation in late summer.

The characteristics and sensitivities of a cold-based glacier on the Tibetan Plateau, where the summer monsoon provides most of the mass input to glaciers, are discussed using an energy-balance model incorporating the process of water refreezing. The model accurately represents the observational results related to the mass balance of Xiao Dongkemadi glacier on the central plateau during 1992/93. Our data revealed that the mass balance of cold glaciers cannot simply be described by the surface mass/heat balances, because about 20% of infiltrated water is refrozen and thus does not run off from the glacier. Model calculations demonstrate that glaciers in an arid environment can maintain their mass since the monsoon provides precipitation during the melting season. Snowfall in summer keeps surface albedo high and largely restrains ablation. Nevertheless, the calculations also make clear that glaciers on the plateau are more vulnerable than those of other regions because of summer accumulation. In the monsoon climate, warming would cause not only a decrease in accumulation, but also a drastic increase in ablation in combination with surface-albedo lowering. Therefore, although glaciers on and around the plateau can be sustained by summer accumulation, they are more vulnerable to warming than winter-accumulation-type glaciers.