GENERAL CHARACTERISTICS There are eight river basins including Pumqu, Rongxer, Poiqu, Zangbuqin, Jilongcangbu, Majiacangbu, Jiazhagangge, Daoliqu in research area. General descriptions of them are given below: Pumqu basin Pumqu river basin is situated in the southwest of
Tibet between the latitude 27º49´N to 29º05´and longitude 85º38´E to 88º57´E. It
is bordered by the upriver of the NianChu river and Doqeen Co in the east; and
Rongxarzangbo, Bo Qu and Paikuu Co in the west; and Nepal, Sikkim in the south;
and YarLungzangbo basin in the north. The total catchments area is 24272 km2. It
is about 320 km in length from east to west and 120 km in breadth from north to
south. It originates from the YeBokangjiale glacier of XiXiabama Mountain. Rongxer basin (Tama Koshi) Rongxer basin (Tama Koshi basin) is situated in the southwest of Tibet between the latitudes 27°56'N to 28°16'and longitudes 86°07'E to 86°32'E. It 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 1439 km2. Among the area, the glacial area is about 324.09 km2. The main river course is about 45 km in length. Poiqu basin (Bhote-Sun Koshi) Poiqu basin is situated in the southwest of Tibet
between the latitudes 27°55'N to 28°30'and longitudes 85°43'E to 86°18'E. It
originates from the Poiqu Co glacier of the south slope of the Himalayan
Mountain. The elevation of the river source is about 5320 m and 2000 m at the
mouth. It starts from the source of the river flowing from east to west and with
the joining of tributaries, it changes the direction near the Nielamu. It enters
Nepal and named Bhote-Sun Koshi river near Nielamu about 7km from north to
south. There are only two meteorological stations-Nie Lamu and Tingri (shegar) in the research region. The stations measure daily rainfall, daily maximum and minimum temperatures, relative humidity, wind speed, and evaporation, atmospheric pressure. Precipitation, air temperature, evaporation and relative humidity play an important role in analysis the climate of basin. Characteristics of these parameters are discussed as the follow paragraphs. Because there are few observed data in the research basin, so we can only do a trend analysis with station which in the research area. These years, with the global warming, which is caused by greenhouse effect, the atmosphere environment has changed. The increase in temperature can have an impact on the condition of glaciers; higher temperature can cause rapid melting of glacier ice. Now many people pay close attention to the urgent problem that is snowline is rising and water level of the glacial lakes is changing. Here is an analysis for the research basin reveals a clear increase in temperature after 1990s (Figure 3.1). The trends are accelerated after 1998. We can describe the climate characteristics of the research area with the data of Nielamu and Tingri meteorological station. The research area belongs to semi-humid region. The data of the Nielamu meteorological station: The annual mean temperature is 3.5°. The lowest month mean temperature is -3.7° which occurred in January. The highest month mean temperature is 10.4° which occurred in July. The highest temperature is 22.4° and the lowest one is -20.6°. The temperature data of Tingri station show same warm trend (Figure 3.3). Figure 3.1 : Annual temperature trends for the research regions The research area is situated at the
upstream of the Ganges and the North slope of the Himalayan Mountain. It is also
the main vapor passage, which the southwestern monsoon going into the
mountainous region of western of Tibet. So the precipitation in this area is
dominated by a southwestern monsoon, the rainfall decrease from south to north.
The maximum precipitation is about 3000mm in the south and 500mm in the north.
Figure3.2 Annual precipitation trends of Nelamu station
Figure 3.3 Annual precipitation and temperature trends of the Tingri station
Evaporation plays a very important role in water balance. Evaporation is influenced by temperature, humidity, solar radiation, and wind speed. The evaporation increase from south to north: La zi is 2800mm, Tingri is 2550mm, and Nie lamu is 1600mm. There is no more changing for every year; Maximum annual evaporation is less than 1.5 times that of the minimum value. Because much of the river in
Himalaya-China region originate from modern glaciers, and many glaciers such as
Rong bu glacier distribute around it. Glaciers and snow area is about 25%. The
supply runoff belongs to groundwater mix with snowmelt and precipitation. Annual
mean runoff is about 50*108 stere.
The GLOF events have been occurred in Tibet especially the period from 1998 to now. The analysis result of Pumqu river basin show that runoff has a increasing trend from 1990s to now; the temperature are growing up; snowmelt increasing and the trend of precipitation is similar to the temperature. Obviously, there is a very important role played in analysis the flood by snow and ice melt in the basin. We should pay close attention to the effect of global warming on the regional hydrology. Particularly, the basin just like Pumqu and Poiqu that distribute a lot of glaciers, it needed real-time monitoring, which will reduce the hazard to the minimum.
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