The Himalaya-China region are situated on the south
of the Tibetan Autonomous Region (TAR) of the Peoples’ Republic of China. The
research regions include Pumqu, Poiqu, Rongxer, Jilongcangbu, Zangbuqin,
Daoliqu, Jiazhagangge, Majiacangbu (see figure 2.1). The total area of the
Himalaya-China research regions within China is 38325 km2. The Himalaya-China
regions have average altitude above 4500 m and receive abundant precipitation of
monsoon form Indian Ocean, both of them providing favorable topography and
climate condition to develop glaciers.
Fig 2.1 The position of Himalaya-China research regions Being
located on the leeward side of the Himalayan range of China
receive considerably less precipitation than the southern Himalayan range.
Generally, the precipitation in the Tibet basin decreases from west to east and
also from south to north.
Meteorological data such
as temperature, rainfall, and evaporation of the Himalaya-China region are
available from the meteorological stations at Tingri from 1960 to 1987. The
annual distribution of rainfall in the region is not uniform. About 96% of the
annual precipitation occurs only in the summer season from June to September.
There are two distinct wet and dry seasons in the basins, but in its southern
part, the seasonal distribution of rainfall is reported to be even and the
precipitation from June through September is approximately 50% of the annual
precipitation.
The mean elevation of the Himalaya-China region is above 4,500 masl. Therefore,
the annual mean air temperature is low because of the high altitude. The annual
mean temperature at Tingri is 2.7 degrees centigrade and the extreme mean
monthly temperature from 1970 to1999 ranged from -9.9 to 13.2°C.
From November to March, the temperature falls gradually below zero. The
variation of air temperature from year to year is small, but the diurnal
variation of the temperature is very large. Evaporation is extremely high
due to strong wind, high solar radiation, and low humidity. The annual mean
evaporation (1971-1980) observed at Tingri is 2,553mm. The highest evaporation
rate occurs in the months of May and June and the lowest in December and
January. The annual evaporation in Chentang, the lower reaches of the Pumqu
River basin near the Nepal/China boarder, is estimated at about 1,000mm. The river systems in the Himalaya-China region are well
developed (see Figure 2.2). The main tributaries of the Pumqu River are Rongpuqu,
Yairuzangbo, Natangqu and Ganmazangbo. The left affluents of the Pumqu (Arun)
River are Pamjuqu, Lopu, Loloqu, Yairuzangbo and Ganmazangbo are the right
tributaries. Drainage areas and observed discharges of the main tributaries are
presented in Table 2.1.
The nine main affluents of Poiqu
(Bhote-Sun Koshi) River are Lazapu, Tongpu, Gyaiyipu. Koryagpu, Targyailing,
Karrup, Congduipu, Zhangzanbo and Pumqu. It is about 80 km in length and the
total catchments area is 1987 km2. Rongxer river (Tama Koshi) originates from the DuokaPula Mountain which elevation is about 5611m. There are so many glaciers at the source of the river. The total catchments area is 1484 km2. The main river course is about 45 km in length. Figure 2.2 The River System in Himalaya-China Region The Himalaya-China region is located in the
middle of the Great Himalayan Range. The geological and geomorphological
features have mainly depended on the upward motion of the Himalayas since the
end of the Tertiary Period. A
glacier is a huge flowing ice mass. The flow is an essential property in
defining a glacier. Usually a glacier develops under conditions of low
temperature caused by the cold climate, which in itself is not sufficient to
create a glacier. There are regions in which the amount of the total deposited
mass of snow exceeds the total mass of snow melt during a year in both the polar
and high mountain regions. A stretch of such an area is defined as an
accumulation area. Thus, snow layers are piled up year after year in the
accumulation area because of the fact that the annual net mass balance is
positive. As a result of the overburden pressure due to their own weight,
compression occurs in the deeper snow layers. As a consequence, the density of
the snow layers increases whereby snow finally changes to ice below a certain
depth. At the critical density of approximately 0.83g cm-3, snow
becomes impermeable to air. The impermeable snow is called ice. Its density
ranges from 0.83 to a pure ice density of 0.917g cm-3. Snow has a
density range from 0.01g cm-3
for fresh snow layers just after snowfall to
ice at a density of 0.83g cm-3. Perennial snow with high density is
called firn. When the thickness of ice exceeds a certain critical depth, the ice
mass starts to flow down along the slope by a plastic deformation and slides
along the ground driven by its own weight. The lower the altitude, the warmer
the climate. Below a critical altitude, the annual mass of deposited snow melts
completely. Snow disappears during the hot season and may not accumulate year
after year. Such an area in terms of negative annual mass balance is defined as
an ablation area. A glacier is divided into two such areas, the accumulation
area in the upper part of the glacier and the ablation area in the lower part.
The boundary line between them is defined as the equilibrium line where
the deposited snow mass is equal to the melting mass in a year. Ice mass in the
accumulation area flows down into the ablation area and melts away. Such a
dynamic mass circulation system is defined as a glacier. A
glacier sometimes changes in size and shape due to the influence of climatic
change. A glacier advances when the climate changes to a cool summer and a heavy
snowfall in winter and the monsoon season. As the glacier advances, it expands
and the terminus shifts down to a lower altitude. On the contrary, a glacier
retreats when the climate changes to a warm summer and less snowfall. As the
glacier retreats, it shrinks and the terminus climbs up to a higher altitude.
Thus, climatic change results in a glacier shifting to another equilibrium size
and shape. According to the glacier inventory of 1990, there are 1578 glaciers in the Pumqu, Poiqu, Rongxer, Jilongcangbu, Zangbuqin, Daoliqu, Jiazhagangge and Majiacangbu basins in China, with an area of 2906.017 km2. The present study shows 1578 glaciers covering area of 2864.33 km2. Figure 2.3 The Distribution of Glaciers in the Himalaya-China regions The study of glacial lakes is very important
for the planning and implementation of any water resource development project.
Past records show that glacial lakes have produced devastating floods and damage
to major constructions and infrastructure. In 1987, a glacial lake inventory was
made for the Poiqu and Pumqu river basin with large-scale topographical maps and
aerial photographs.
Several GLOF events have occurred over the past
few decades in the Himalaya-China region, causing extensive damage to roads,
bridges, trekking trials, villages, as well as loss of human life and other
infrastructures. |