BRIEF DESCRIPTION OF METHODS
The data used in this study include the TM and ETM+ images acquired in 1990 and 2000 respectively to compare each other and to detect glacier change, as well as 1:50,000 topographic maps published in the 1980s and the Glacier Inventory of China-the Ganga Drainage basin and the Indus River Drainage basin as reference. The guide for compilation of the World Glacier Inventory suggests that the code system must be made on the subordination relation and direction of rivers progressively. The lettering and numbering should start from the mouth of the major stream and proceed clockwise round the basin. For convenience, the code in this inventory is basin name plus glacier coding. In order to be consistent with the data of glacier inventory, each glacier given a number proceeding clockwise. The classification of glaciers is based on the morphological classification of glaciers by the World Glacier Monitoring Service (WGMS) (1989). Details of the classification are mentioned in Chapter 4. Changes of glaciers during two periods can be extracted from these images and maps, and then analyzed using GIS techniques. The outline of glaciers in 1990 and 2000 were obtained by TM and ETM images respectively. The attributes related to elevation are obtained from topographic maps. Other attributes such as area, length of glaciers are acquired and computed in the GIS software Arcview. The glacial area and length is measured with the help of GIS. Since the ice thickness data are not available, it is estimated from the equation developed for the Tianshan Mountains (Chaohai Liu and Liangfu Ding 1986) H = -11.32 + 53.21F0.3 Where H = means ice thickness (m) and F = glacier area (km2) The ice reserves were estimated by multiplying the mean thickness by the glacial area. CHARACTERISTICS OF GLACIERS IN 1990 According to WGI, the test regions include 18 sub-basins shown in Figure 2.4. There are 1810 glaciers altogether covering an area of 2991.1635 km2. Table 7.1 shows the number of glaciers and the area covered by those glaciers for each sub-basin.
The Pumqu_F sub-basin, also the smallest one, has the smallest number of glaciers and glacier area. The number of glaciers in the Pumqu_C and Pumqu_G sub-basin is 250 and 183 respectively, but Jilongcangbu sub-basin accounts for the largest glacier area. This is only a simple statistic, which couldn’t show the mean condition about size of glaciers in each basins. Further analysis as follow:
Glaciers in the Pumqu_F sub-basin are very small, about 0.9724 km2 on average, while Jilongcangbu has the largest glacier area.
Table 7.3 depicts the share of glacier number within different area-size classes compared to the total number of the glaciers, the share of glacier area within different area classes compared to the total glacierized area respectively. As is well known, the general characteristics of Himalayas-type glacierization are that most glaciers are small and cover a small area. For example, the numerous small glaciers with an area of less than 1km2 cover only about 14.48% of the total glacier area. CHARACTERISTICS OF THE GLACIERS IN 2000 The ETM images acquired in 2000 were co-registered with the topographical maps and the TM image in the image processing software (ENVI). Ground control points (GCP) were selected and easily identified on both topographical maps and the RS image. By selecting enough ground control points, the root mean square error (RMS) of the co-registration was limited to 1 pixel. But in the region with large altitude difference, the error can reach 2 pixels. In order to detect the change of glaciers during 10 years more easily, glacier outline were digitized form the image. Within the Himalaya-China region, there are 1578 glaciers altogether covering an area of 2864.33 km2. The glacier distribution in each sub-basin is showed in the Table 7.4.
By comparing the data of different periods, we analyzed the activity of glaciers. The total trend is that the glaciers are retreating, which resulted from a combination of natural climatic evolution and reinforced by anthropogenic greenhouse gas. With the retreat of glaciers, rapid melting of glacier ice and snow can result in the rise of glacier lake level, which then becomes greatly vulnerable to GLOF. So, the research of glacier change is very important for human safety and economy.
These latest decreases in area were 1.43% during last 10 years. Glacier changes from the 1990 to 2000 in the eight sub-basins are given in Table 7.5. The percentage of area change for different periods were calculated as the ratio of the total decrease in area to the total area in the 1990 before area changes occurred. For example, the percentage of area change from the 1990 to 2000 are taken as (S1990 -S2000) / S1990 . During the 1990, the total area of all 1578 measured glaciers was 2906.017 km2, which is (seen in Table 7.5) 41.687 km2 more than those in 2000; thus the glacier area decreased by 1.43% from the 1990 to 2000. The decrease was the greatest (-10.65%) in the Rongxer_A sub-basin, and second largest (-3.56%) in the Pumqu_E sub-basin. There are very less change in the other sub-basin. |