Disappearing Water Towers: Nepali Himalayas Case Study

Eurasia News

Disappearing Water Towers: Nepali Himalayas Case Study

By Agha Iqrar Haroon

Climate change is the reality of our era and mountain areas are particularly vulnerable to climate change. Change in temperature is contributing rapid melting of glaciers that is leading to the formation and expansion of glacial lakes. This situation contributes an increase in the number of glacial lake outburst floods (GLOFs). If the present trends persist, the glacier ice mass will gradually be reduced, which will impact on the availability of water resources. Meteorological parameters such as temperature and rainfall play an important role in determining glacier changes. Surface where water is in solid form is decreasing in size day by day but there is lack of data about such cryosphere.

Scientists and experts working in Himalayas are collecting credible data about changes going on in glaciers and they maintain glacier inventories through different approaches and methods. We have enough data to understand that water towers are disappearing, minimizing, thinning, receding and retreating all over the world but we did not have comprehensive data about Himalayan region and Nepal unless we got recent report published by Integrated Mountain Development (ICIMOD).

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The report title “Glacier Status in Nepal and Decadal Change from 1980 to 2010 Based on Landsat Data is authored by Samjwal Ratna Bajracharya, Sudan Bikash Maharjan, Om Ratna Bajracharya and Sarju Baidya. Royal Norwegian Embassy, Kathmandu Nepal provided financial support for this publication.

It may be mentioned that first inventory of glaciers and glacial lakes in Nepal was published by ICIMOD in 2001. It was based on topographic maps published by the Survey of India from 1963 to 1982, satellite images from 1999 and 2000, and aerial photos taken from 1957 to 1959 for areas for which no topographic maps were available and supplementary field work. The inventory provided a first overview of the glaciers in the country, but the data were based on a wide temporal range and derived from different sources. The 2001 inventory also mapped all lakes at elevations higher than 3,500 metre above sea level (masl).

Another inventory of glacial lakes was published by ICIMOD in 2011 based on an analysis of Landsat satellite images and 1,466 lakes were identified with a total area of 65 km2.

Latest technology is used for data collection

Now latest available scientific tools and technology are being used for this study based on a semi-automatic standardized analysis of satellite images with post-processing database management in ArcGIS. The methodology is an improved version of methods developed by global initiatives like the World Glacier Monitoring Service (WGMS), Global Land Ice Measurement from Space (GLIMS), and GlobGlacier.

The semi-automatically derived glacier outlines from 2010 were overlain separately on the images used to approximate 1980, 1990, and 2000, and the glacier outlines were modified manually for the respective years and used for change analysis. Clean-ice and debris-covered glaciers were mapped separately for 2010 to support studies of water resources assessment and climate change impact.

In an additional case study, glacier outlines for the four decades in the Langtang sub-basin in central Nepal and Imja sub-basin in eastern Nepal were analysed and compared with decadal temperature change.

Report covers four major river basins

The glaciated area in Nepal contains the upper reaches of four major river basins with 19 sub-basins, all of which are part of the Ganges basin system: the Mahakali, Karnali, Gandaki, and Koshi. The glacier-fed river basins have a total area of 89,457 km2, or about 61% of the total land area of Nepal. All of the river basins have one or more sub-basins with transboundary sections. The mapping processes were limited to the sections within Nepal and the data refer only to the Nepal area of the basins. This report covered glacial behaviors of all four major river basins in detail.


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Global warming and increase in temperature

This comprehensive and technical report is basically an encyclopedia of glaciers and is full of technical data about glaciers of Nepal and provides a complete scientific picture of the status of glaciers in Nepal since 1980. Authors of this report have very successfully managed to share scientific information with common readers in a relatively comprehendible language thereby encouraging readers to get 30 years data without having the need to consult experts.

Global warming and increase in temperatures is playing havoc with water towers—glaciers all over the world, however the fragile Himalayas and its valleys receive stronger impact due to higher rate of changes in temperatures.  The average annual temperature in the Nepal Himalayas between 1971 and 1994 increased by 0.15 to 0.6°C per decade which is two to eight times higher than the global mean warming of 0.74°C over the last 100 years. Warming can affect the glacier distribution and seasonal snow cover spatially and temporally both by increasing the melting rate and reducing snowfall in favour of rain.

Case study of Langtang valley and Imja valley

Though this glacier inventory covers and discusses entire Nepal but it also offer a special study regarding temperature increase in the two mountain valleys –Langtang valley and Imja valley in support of impact of global warming over glaciers and over all cryosphere. Langtang valley and Imja valley were chosen for special study because best reliable data and record about temperature are available from these two valleys.

The total glaciated area showed a loss of just over 25% of the original extent in Langtang and Imja valleys in the 30-year study period but this change was not identical for all glaciers. The type, size, slope, aspect, elevation, and debris or other cover of a glacier, all affect the extent and rate at which it will be affected by changes in climate.

The six glaciers under observations showed overall area losses ranging from 16 to 51% of the initial area. Data indicates that low lying small glaciers reduce in size more rapidly than bigger glaciers.

Disappearance and lose of ice/snow at Imja glacier is at the lower end of the glacier where lake starts, resulting the glacial lake to expand and subsequently reducing the glacier.  Same trend was shown in Langtang valley. Authors recommend that such differences should be studied in more detail and for more glaciers, to develop more precise modeling of future impacts of climate change.

Langtang valley lies within the Trishuli sub-basin of the Gandaki basin in the central region of Nepal and the Imja valley lies within the Dudh Koshi sub-basin of the Koshi basin in the eastern region. These valleys were chosen for this study because they are heavily glacierized and some long-term climatic data from close by points was also available from the Department of Hydrology and Meteorology (DHM) of the Government of Nepal. The temperature change was investigated over a period of 21-years for which data were available (1988 to 2008). There was a considerable fluctuation in average annual temperatures, but regression analysis showed an overall increase in annual mean temperature in Langtang of 4.2°C, with a rate of change at 0.12°C/year, and in Khumbu of 0.3°C; with a rate of change at 0.09°C/year. The overall increase was higher between 1998 and 2007 than between 1988 and 1997 but a small downward fluctuation in Langtang after 2004 was also reported. Analysis of five and ten-year moving averages indicated that although both the maximum and minimum temperatures showed a rising tendency, only the increase in minimum temperature was significant. An increase in minimum temperatures could have a more dramatic effect on the surroundings than an overall increase in temperatures partly because it is more likely to raise the temperature above the 0°C threshold, thus extending the melting season.

The temperature rise is considered to be the primary factor responsible for glacier retreat. Authors recommend future studies are needed to consider other factors that affect glacier dynamics, such as size, slope, shape, debris cover, and contact with water bodies, in more detail.

Important findings

The report confirms observations of previous glacier studies that glacier decline/ recession is one of the key indicators of climate change. Temperature change is considered to be one of the most important factors in glacial retreat, advance, and change in surface area although glacier mass may also be influenced by changes in precipitation, solar radiation, and the presence of surface matter. As the temperature rises, the rate of melting in the lower part of a glacier becomes greater than the rate of accumulation of snow in the upper part. The temperature rise may also lead to a change in precipitation from snowfall to rain, which will also affect the amount of accumulation and rate of melting. As a result of these effects, the glacier will lose more mass (size) and may retreat upslope (vanishing from its tale).

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The overall glacier area in Nepal decreased by 24% (1,266 km2) and the estimated ice reserves by 29% (129 km3), while the number of glaciers increased by 11% (378) over the 30-year period. The same pattern was observed in all basins, although with differences reflecting the different elevation, type, and concentration of glaciers in each. The decrease in glacier area accompanied by increase in the number of glaciers is clear evidence of fragmentation as a result of uneven ‘shrinking’ of individual glaciers. In terms of elevation, the greatest loss of area was in the elevation band 5,000 to 6,000 metre above sea level (masl) (mainly below 5,800 masl), between 1980 and 1990.


Unusual glacial behaviour during the decade of 1980-1990

This report indicates that something seriously went wrong or abnormal in Nepali Himalayas during the decade of 1980-1990. What went wrong and why? , is a mystery and needs further study.

Report discusses the behavior of glaciers in Nepal and Accumulation (where the formation of ice is faster than its removal) and Ablation (where the sum of melting and evaporation is greater than the amount of snow added each year) of glaciers.

Data available in this report indicates an unusual and strange patron and rate of loss of glacial area between 1980 and 1990 when change was observed almost twice that in the subsequent two decades (1990–2000 and 2000–2010). This is not same period when maximum increase in temperature in this area was observed so we cannot say that extreme heat resulted this drastic change. During the last 30 years, the total number of glaciers increased in Nepal by 11% with the greatest increase between 1980 and 1990—the same period when heavy loss of ice and snow covered area that is called “cryosphere” in technical terms was reported.  Experts believe that further study is needed to determine whether this reflects a slowing in the rate of change or an abnormal situation in the first period.

Some more interesting findings:

The Ngojumba glacier in the Dudh Koshi sub-basin was the largest single glacier with an area of 79 km2. The largest glacier identified in the 2001 ICIMOD inventory was Ktr_gr 193 in the Tamor sub-basin. This glacier has reduced in size and fragmented into two glaciers, and is no longer the largest in Nepal. The present inventory identified the Ngojumba glacier in the Dudh Koshi sub-basin as the largest individual glacier in 2010. However, the area of this glacier was also lower than measured in the 2001 inventory (78.7 km2 compared to 92.4 km2).

Overall temperature increased in Nepal Himalayas

The average annual temperature in the Nepal Himalayas between 1971 and 1994 increased by between 0.15 and 0.6°C per decade which is two to eight times higher than the global mean warming of 0.74°C over the last 100 years . Warming can affect the glacier distribution and seasonal snow cover spatially and temporally both by increasing the melting rate and by reducing snowfall in favour of rain.

Glaciers have been thinning and retreating in many parts of the world. Changes in glaciers provide some of the clearest evidence for climate change, and glacier shrinkage, and in some cases disappearance, indicates the speed of the present change on a global scale. These changes have implications locally and regionally for water resources, and globally for sea level rise. The associated increase in regional and local hazards is also increasing risk for communities. In view of this, extensive efforts have been made internationally to improve our understanding of the ongoing changes in glaciers and the pattern of global warming, as well as projecting future scenarios using global and regional climate models.


The results show clearly that the glacier area in the Nepal Himalayas is decreasing at a rapid rate, and that individual glaciers are shrinking, retreating, and fragmenting. The changes appear to be linked primarily with a marked rise in average temperature associated with global climate change.

The extent to which changes in precipitation play a role, including total amount, seasonal distribution, and change from snowfall to rainfall, is not yet known. The changes have a number of implications. The high Himalayan region contains important fresh water reserves in the form of glacier ice, and glacial shrinkage will have an impact on the long-term availability of freshwater from these reserves. Initially, increased melting of glaciers might lead to an increase in glacial runoff and thus river flow lasting some decades, but this will be followed in the long term by a reduction. Furthermore, glacial recession can be associated with the formation and expansion of glacial lakes below the retreating terminus, with the associated risk of a glacial lake outburst flood (GLOF); continued recession may lead to an increase in the number of glacial lakes and in the frequency of GLOF events. Finally, the cryosphere also plays a significant role in regional climate regulation, and change in the glacial area may not only be affected by, but also have a long-term impact on, the regional climate.

Small glaciers, low elevation glaciers, and low sloping glaciers – especially clean-ice type – may be more significantly affected by climate change. Small glaciers have a low thermal mass for buffering change, and low slope glaciers are more vulnerable because a small rise in elevation of the thermal equilibrium will affect a large area of the glacier. Not all small glaciers are vulnerable to disappearance, however, because they commonly exist in heavily shadowed cirque basins, and many are close to steep slopes and receive abundant snow avalanches and wind-blown snow in addition to direct snowfall. As small glaciers retreat closer to the steepest basin slopes, these contributions may increase and make the final disappearance a very slow process. Similarly, not all low slope glaciers are equally vulnerable. Debris-covered glaciers, which tend to have lower slopes, can be insulated from warming by the debris cover and respond more slowly to change unless a lake forms at the terminus. Although some of the smaller glaciers present in 1980 had disappeared by 2010, the actual number of small glaciers increased as a result of shrinkage and fragmentation of previously larger glaciers. The glacier area and estimate dice reserves contributed by small glaciers are comparatively small, but as these glaciers tend to be more sensitive to climate change they may play a more important role proportionately in the loss of ice reserves. The separate information for clean-ice and debris-covered glaciers will serve as an important parameter in climate change models. Clean-ice glaciers respond to climate warming on a shorter timescale than debris-covered glaciers, as a result of the thermal insulation provided by the debris in debris-covered glaciers. As climate warming and netablation proceed, the remaining glacier area is likely to have an increased proportion of debris-covered area. Netablation also causes transition of some relatively clean-ice areas into debris-covered ice as debris accumulates.

Furthermore, as glaciers thin, lateral moraines can destabilize and collapse onto them, adding more debris to the surface. This means that an increase in the percentage of debris-covered glaciers in an area is likely to be an indicator of climate change. The debris-covered and clean-ice area was only differentiated in the images for 2010.

In the future, additional analysis will show whether the proportion of debris-covered area is in fact increasing. Better and longer series of temperature and precipitation data at higher altitudes are needed in order to analysethe causes of the changes in glacier extent in more detail. Long-term hourly measurements of temperature at higher elevations are needed to enable correlation with glacier change, together with measurements of rain and snowfall.

The greatest amount of precipitation in the Nepal Himalayas falls during the monsoon and pre-monsoon seasons.

At higher elevations this precipitation is in the form of snow and contributes to glacial accumulation. Changes in both total precipitation and seasonal distribution may affect the snow available to glaciers for accumulation. The increase in temperature may also result in precipitation falling as rain at higher altitudes than previously. This will affect the glaciers in two ways: less snow will be available to add to the ice mass, and the rain will increase the melting rate of the existing ice. Long-term series are needed as rainfall patterns show considerable variation in individual years.


The lack of data on Nepal’s glaciers is hindering efforts to project future scenarios and develop plans for mitigation and adaption. To some extent this can be addressed using satellite imagery, but selected ground truthing (Ground truth is a term used in remote sensing; it refers to information collected on location. Ground truth allows image data to be related to real features and materials on the ground) and good quality mass balance measurements are needed from a range of different glaciers to facilitate data interpretation. The following are recommended for assessments using satellite imagery.

Small and medium-sized glaciers should be mapped and monitored regularly using high-resolution satellite images.

A repeat inventory of glaciers of Nepal is recommended at intervals of five years to capture the ongoing change.

Names of important glaciers should be mentioned in published data in addition to the GLIMS ID code to aid understanding by non-specialists concerned with local impacts.

On-the-job training in glacier mapping and monitoring using satellite images should be provided as a matter of urgency to the technical staff in Nepalese partner institutes so as to improve the capacity for mapping and monitoring of glaciers, and thus enable regular monitoring of ‘hot spot’ areas with rapidly retreating glaciers. The daily mean temperature data used in this study are averages of the maximum and minimum temperatures and tend to be high and affected by extreme values. Statistically, these mean temperatures may not represent the population mean. Long-term hourly temperature data are needed to ensure that the daily mean represents the population mean, but at present such data are not available.

The hydro meteorological stations should be upgraded with automated data logging systems.

A representative network of high-altitude hydro meteorological stations should be established.

The existing high-altitude stations should be made fully functional to ensure the availability of good quality of data.

Whosoever has interest in mountain development, Himalayan mountains topography, glacierology, climate change and related topics cannot miss to read this latest scientific report published by ICIMOD.


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