M. Nakawo, Research Institute for Humanity and Nature, Kyoto, Japan
ABSTRACT: A rapid shrinkage of glaciers in the Nepal Himalayas has occurred in the last 25 years, despite the fact that the rise in air temperatures has not been as pronounced as the global average. One of the most important reasons for this shrinkage is that snow accumulates in summer and not in winter. Glaciers in the Qilian Mountains, western China, are also fed during summer, and they have deteriorated rapidly as well. Because of this glacier shrinkage, the rate of river discharge has increased slightly and yet people in the river basin have suffered from a water shortage, which is thought to be the result of human activities. Glaciers are an important water resource, in particular in the arid and semi-arid regions of central Eurasia. Glacier studies, therefore, should be combined with studies of social systems and of human culture, taking into account their proactive and reactive effects.
1 GLACIER SHRINKAGE IN THE NEPAL HIMALAYAS
1.1 Retreat of glacier termini
Figures 1 and 2 are photographs of Rikha Samba Glacier, central Nepal, and AX010 Glacier, eastern Nepal, respectively, showing the rapid retreat of these glaciers in the last 20 to 25 years. In case of the Rikha Samba Glacier, the rate of retreat has been about one meter per year (Fujita et al., 1997).
Figure 1: Retreat of the terminus of Rikha Samba Glacier, Hidden Valley, Nepal (Pictures taken by Glaciological Expedition of Nepal, and Cryoshere Research in the Himalayas)
Figure 2: Retreat of the terminus of the AX010 Glacier, Shorong Himal, Nepal Pictures taken by Glaciological Expedition of Nepal, and Cryoshere Research in the Himalayas)
Comparing maps compiled from airborne imagery taken in 1958 and 1992, Asahi (2001) reported aerial changes of every glacier in eastern Nepal, and mapped the distribution of advanced, stationary, and retreating glaciers. In the Khumbu Region, for example, the area of most small glaciers decreased, while a small number of these small glaciers advanced. Large glaciers, whose ablation area is mostly covered with debris, showed no changes in extent. However, they have experienced a loss in ice mass, as their thickness has decreased. This matter will be discussed below.
1.2 Change of glacier volume
Three glaciers were examined with regard to changes in their volume. Rikha Samba Glacier lost 548.8 x 105 m3 of ice during the period from 1974 to 1994. The volumetric difference of Glacier AX010 was 10.4 x 105 m3 between 1978 and 1999, and Yala Glacier lost 9.3 x 105 m3 from 1982 to 1996. When expressed in terms of the thinning rate over the whole glacier, the surface lowering amounted to 0.55m/year on Rikha Samba Glacier, 0.72 m/a on Glacier AX010, and 0.36 m/year on Yala Glacier.
Figure 3 compares these thinning rates with mass balances of glaciers in other parts of the world. In the figure, annual mass balance amplitude is expressed on the horizontal axis, since the mass balance of glaciers with large amplitudes react more greatly than those with small amplitudes (Meier, 1984). As can be seen in Figure 3, Himalayan glaciers of the same amplitude have lost mass at a faster rate than glaciers in other regions.
Figure 3: Rates of glacier thinning in various parts of the world (Fujita et al., 1997). For a given annual mass balance amplitude, Himalayan glaciers have lost mass at a faster rate than glaciers in other regions.
1.3 Supraglacial moraine
In the Nepal Himalayas, the ablation areas of large glaciers are usually covered with debris. Ice mass under this debris was considered stagnant, because thick debris on the surface was thought to play the role of an insulator, and ice melt below was considered negligible. Repeated surveys have indicated, however, that the glacial thickness has decreased at a rate of about one meter per year in the case of the Khumbu Glacier, one of the debris-covered glaciers in the Khumbu Region. A similar rate of thinning was observed on the Lirung Glacier, another debris-covered glacier in Langtang Khola, central Nepal.
It is difficult, in the case of such debris-covered glaciers, to estimate the average thinning rate for the whole glacier, because less information is available with regard to the accumulation area of debris-covered glaciers, which tend to be located at very high altitudes. The significant thinning in their ablation area, however, indicates that debris-covered glaciers also have lost their mass at a high rate, although the exact rate has yet to be assessed.
It can be stated, that over the last few decades glaciers have deteriorated rapidly in the Nepal Himalayas. This shrinkage may have been caused by recent global warming, but careful investigations will be necessary before a firm conclusion can be reached.
2 RECENT WARMING IN NEPAL
2.1 Instrumental data
In the previous chapter, we showed that the rate of glacier shrinkage has been significant in the Nepal Himalayas. Does this mean that there has been a similarly significant rise in air temperatures?
Figure 4 shows daily maximum air temperature data, averaged for all of Nepal, taken from rural observation sites only, and discarding temperatures recorded at city sites, where heat island effects may have occurred. The record shows an increase after 1970, as shown by the dotted line. The rate of temperature rise seems to have increased after 1980, as shown by the solid line.
Figure 5: Change of summer air temperature anomalies (°C), reconstructed by dendrochronology.
Cook et al. (2003) compiled data based upon tree-ring analyses carried out in Nepal. They also showed a warming trend into the late-20th century, but only in winter. In summer, the temperature seems to have even decreased, suggesting that warming was not pronounced in Nepal.
Although temperatures have increased in Nepal, rate of the warming is by no means large enough to explain the rapid shrinkage of the glaciers.
3 THE CAUSE OF THE RAPID SHRINKAGE OF GLACIERS
3.1 Summer Accumulation
Figure 6 shows seasonal changes in air temperature and precipitation observed at the Rikha Samba Glacier, at an elevation of more than 5000 m. Precipitation occurs mostly from June to September, during the summer monsoon season. During summer, when this precipitation occurs, air temperatures are a few degrees above freezing. For the remainder of the year, air temperatures generally remain below the freezing point.
Figure 6: Seasonal variations in air temperature and precipitation at the Rikha Samba Glacier, central Nepal, October 1998 to September 1999 (Fujita et al. 2001).
It was observed, in the Nepal Himalayas, that precipitation is in a solid phase when the air temperature is above 1°C, and in a liquid phase when air temperatures are above 4°C (Ageta et al., 1980; Ueno et al., 1994).
Looking at the temperature record shown in Figure 6, it appears that snow accumulation on glaciers generally takes place during the monsoon season (“summer-accumulation type glaciers” after Ageta and Higuchi 1984). The air temperature during this period, therefore, is very critical, as it determines the aggregational state of precipitation. When the air temperature rises slightly, solid precipitation becomes liquid and the amount of accumulation decreases significantly. In other words, the amount of annual accumulation, on Himalayan glaciers, is very vulnerable to warming.
Because the major accumulation season is in the summer, Himalayan glaciers are often covered with new snow during the summer months. The summer, however, is also a major ablation season for glaciers. Frequent snow cover, in particular in the ablation area, would hinder the ablation of glaciers due to the high albedo of new snow. Warming in the Himalayas, therefore, would lead to less frequent snow cover, and as a result, ablation is accelerated. This is the “albedo effect”, resulting from warming of the atmosphere.
Warming would certainly accelerate the ablation of glaciers, even without this albedo effect. Himalayan glaciers are, hence, very vulnerable to warming, because of the combination of three causes: a decrease of accumulation due to the phase change of precipitation, the albedo effect’s acceleration of ablation, and accelerated ablation due to an increase of sensible heat fluxes.
Glaciers in other parts of the world are mostly fed during winter. With warming temperatures, their ablation increases, but the other two causes for the shrinkage of Himalayan glaciers, would not affect their mass balance, because accumulation takes place in winter.
Therefore, it is concluded that the rapid shrinkage of Himalayan glaciers, even given a mild warming trend, results primarily from the fact that glaciers are fed during the summer: accumulation and ablation take place simultaneously and both are affected towards a more negative mass balance.
3.2 Biological activities
Figure 7 is a photograph of Yala Glacier, central Nepal, taken in summer 1994. The glacier surface is dark, almost black. The black material was found to be micro biological communities, such as green algae and cyanobacteria, as shown in Figure 8.
Figure 7: Yala Glacier, covered with black biological matter (after Takeuchi).
An abundance of these organisms results in a low surface albedo and accelerates ablation. The quantities of this material are several times greater for Himalayan and Tibetan glaciers than it is for Patagonian, Alaskan, and Arctic glaciers (Takeuchi et al., 2006). It remains unclear why this growth is typical for Asia. This biological community, however, may have led to a more rapid shrinkage of glaciers in the Himalayas than of glaciers in other regions, although we are not sure whether the biological activities are only recent phenomena.
Figure 8: Microphotograph of cyanobacteria (after Takeuchi).
4 WATER SHORTAGES IN THE HEIHE BASIN, WESTERN CHINA
4.1 Stable river flow in a warming climate
The rapid shrinkage of glaciers in the Himalayas has been reported above, and the major cause of this is seen in summer accumulation. Glaciers in western China are also of the summer-accumulation type and therefore can be expected to have shrunk at a high rate as well.
We have examined the 7-1 Glacier in the Qilian Mountains. The terminus has retreated by about 100 to 140 meters in the last 25 years, at an average of 4 m/year. The glacier has lost approximately one tenth of its mass in the same period. This was determined through a comparison of our recent observation data and a glacier map prepared by the Lanzhou Institute of Glaciology and Geocryology in 1975. The rate of mass loss is consistent with an average rate of thinning of about 0.3 m/year for the whole glacier (Sakai et al. 2006). The rate is not as rapid as it is for the Himalayan glaciers, but considering that both accumulation and ablation are not very large on this strongly continental glacier, the retreat is significantly high.
At Zhangye, one of the closest cities to the glacier, a gradual increase in air temperatures has been observed, at a rate of about 0.5 °C over the last 50 years. Stable isotope content in an ice core from Qilian Mountains indicates a recent temperature rise also in the mountains and this warming may serve to explain the deglaciation.
Glacier devastation leads to an increased river discharge since thinning glaciers supply additional water to stream flow.
Precipitation appears to have increased at Zhangye. At high elevations, however, it seems to have decreased slightly, when precipitation in the mountains is estimated from an ice core.
While warming may have caused a decrease in precipitation, as reported at several sites in arid and semi-arid regions, the increase in glacier melt would, to some extent, compensate this loss. There are data to suggest that the volume of runoff flowing from mountains to the middle reaches of the river, where communities make use of irrigation agriculture, has not changed over the past 50 years. In fact, if anything, runoff has increased only slightly (Figure 9).
Figure 9: River discharge of the Heihe River. The solid line indicates discharge from the mountains to the middle reaches, measured at Yingluoxia (1674 m a.s.l.) and the dotted line with an open circle shows the discharge from the middle reaches to the lower reaches measured at Zhengyixia (1280 m a.s.l.) (y-axis is in Gt/year).
The Heihe River is a typical inland river. It originates in the Qilian Mountains at the border of the Qinghai and Gansu provinces in western China, and flows north before finally emptying into a couple of inland lakes in the Inner Mongolian Autonomous Region. After Tarim River, Heihe is the second largest inland river in China, with a basin area of approximately 130,000 km2.
In the Heihe River Basin, annual precipitation ranges from 200 to 800 mm in the mountains, while it is only about 100 mm in the lowlands where most people are living. These communities strongly depend on water coming from the mountains, including the melt water from glaciers. It is of great importance, therefore, to have a stable river discharge from the mountains. As we have described above, the discharge from the mountains is generally stable as the climate warms, and people do not appear to be suffering from the effects of climate change.
4.2 Water shortages and measures taken
Although annual discharge from the mountains has not changed significantly, various symptoms of water shortage have appeared, particularly in the lower reaches. Examples of this include falling water levels in wells, forcing people to dig new, deeper wells in order to secure water, a decline in natural riparian vegetation, reductions in forested areas, and substantial deterioration in the condition of grasslands surrounding these forests. In addition, two lakes into which the Heihe River once flowed have disappeared, the first in 1961 and the second in 1992.
Figure 9 also shows the river discharge from the middle reaches to the lower reaches where water shortages have been remarkable. As can be seen, the discharge to the lower reaches decreased from around 12 Gt/year in the 1950s to about 8 Gt/year in 2000, a decrease ofroughly one third in half a century.
The difference between the discharge from the mountains and the amount of water to reach the lower reaches can be accounted for by the amount of water consumed in the middle reaches, where vast areas are irrigated for agriculture. Water consumption has more than doubled during this period, from 4 Gt/year to 9 Gt/year (Hidaka and Nakawo, 2006). The area of irrigated land also increased sharply. It was three times larger in 2000 than it was in the 1950s (Wang and Cheng, 1999).
A couple of measures have been adopted in response to this water shortage. First, the presence of forests in the mountainous region is thought to be important to stable river flow from the mountains to the lowland areas. Animals raised and kept by pastoral people are considered to damage the mountain forest by eating the young leaves of trees. It was recommended, therefore, that the pastoral people, together with their animals, relocate to the lowland areas, where they could either become agricultural farmers or continue to keep livestock, but in barns. This was called the “Ecological Relocation Policy” (Nakawo et al., 2010).
In the middle reaches, some Yugu people, an ethnic minority, have kept their animals on a limited area of grassland. Because of recent grassland deterioration, they have been encouraged to relocate to a “model village” where houses and barns have been provided for agricultural activities and the keeping of livestock.
In the lower reaches as well, pastoral Mongols have been asked to relocate either to an oasis in the desert zone or an area in the desert away from the river, because it is thought that their animals have been causing damage to the riverside forests.
Let us now consider the results of this “Ecological Migration” policy.
Some of the pastoral people who relocated to new sites in the middle reaches became farmers, who, however, required water for their farming activities. Water use from the river is strictly limited, partly by regulation and partly by water rights that those who relocate do not have access to. They turned then to the use of groundwater, whenever possible. This accelerated groundwater consumption because the original farmers had also become more dependent on ground water.
Some immigrants still keep their animals in barns at the new site. They are required, however, to feed their livestock with grass they have planted, whereas before they had made use of natural grasses. For this grass cultivation, they certainly require water, as do those immigrants who became farmers.
As a result, the amount of water consumed in the middle reaches increased rapidly, by about 6 times, during the 20 years from 1980 to 2000.
In the lower reaches, we can find similar changes among those who were relocated to the oasis. They too require additional water for farming, and this is taken from groundwater. People that have relocated to desert areas, away from the river, also require water for their animals and for daily life. Although the grass grown to feed livestock is fed by natural precipitation, they have also dug new wells.
In any case, the consumption of groundwater has increased rapidly, leading to a significant lowering of the groundwater level, and “Ecological Relocation” is partly responsible for this overuse of groundwater.
Stable isotope analysis of groundwater from the Heihe River Basin indicated that it had formed over a period of hundreds of years. Groundwater is extremely important. It should be used in a sustainable way and not be consumed by one generation. Thus, a water resources management has to be established, taking into account groundwater as well.
“Ecological Relocation” was undertaken primarily to restore and/or to maintain a good ecological condition by overcoming the water shortage. Another incentive for this migration policy, however, has been an improvement in the economic condition of migrants, helping them to escape from poverty. Relocated pastoral people, however, have to spend additional money for the excavation of deep wells, since shallow wells are no longer practical. The details of their economic condition are beyond the scope of this paper, but ”Ecological Relocation” in the Heihe Basin does not seem to have been successful in this respect either. In fact, “Ecological Relocation” appears to have resulted in a deterioration of the culture of the migrants, although this is beyond the scope of this paper as well.
5 SUMMARY
In the Himalayas, recent warming has by no means been very rapid, and it is thought to be a rebound from the little ice age. It is rather gentle, when compared with the average rate of temperature rise for the northern hemisphere. Despite this, glaciers in the Himalayas have shrunk at a marked rate.
As shown above, the rapid shrinkage of glaciers is mainly caused by the fact that glaciers are fed during the summer months, when also accumulation is at its maximum.
Glaciers in the Qilian Mountains in western China, which are also fed during the summer, have suffered a loss of mass at a significant rate as well. This shrinkage has supplied additional water to the rivers, offsetting a decrease in precipitation. As a result, the rivers have maintained stable levels even as the climate has warmed.
River water from the mountains is very important in the arid and semi-arid regions of central Eurasia and people strongly depend on stream flow from the mountains. Due to the large fraction of glacier melt in central Eurasian rivers, it is of great importance to monitor glacier changes in keeping with global warming. For example, the contribution of glacial melt water to the total river discharge was found to be roughly half for the Yurungkax and Keriya rivers flowing from the Kunlun Mountains to the Taklamakan Desert (Figure 10).
Figure 10 Contribution of glacial melt water to the total river discharge for two rivers in the Kunlun Mountains (Ujihashi & Kodera, 2000)
However, water shortage is a major issue in the Heihe River Basin, even though discharge from the mountains is generally stable. This suggests that we must take into account how water is distributed, or shared, by different groups of people, i.e. human activities.
We have also seen that one of the measures for solving the water shortage, namely “Ecological Relocation,” has not been effective. In fact, the outcome appeared to be completely different from what was intended.
It should be stressed, therefore, that glaciological and/or hydrological studies should be combined with social and human studies. To overcome global environmental problems, integrated studies are essential, as we have seen in the case study of the Heihe River Basin.
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Slight revision of the paper appeared in 2009
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