the portion of the Tibetan Plateau included in those basins. According to the committee’s charge, the areas of major concern are those where the water supply for a significant population could be influenced by changes in the region’s glaciers. Figure 1.4 shows the percentage of glaciated area within the river basins of the HKH region. The Indus, Ganges, and Brahmaputra basins combined contain nearly three-quarters of the region’s glaciated area. Except for the interior basins (labeled as Himalayan Endorheic basins in Figure 1.3c), the other river basins each contain less than 5 percent of the region’s glaciated area. The Committee includes some discussion of the part of the region covered by the Endorheic basins in Chapter 2, Physical Geography, particularly in the section on ice core data (see Figure 2.14). Because the population density of the Tibetan Plateau is very small (see Figure 3.1), it follows that very few people depend on the interior basins for water supply, and any glacier-related changes to the water supply in those basins would not affect a large number of people. Thus the focus of Chapter 3, Human Geography and Water Resources is on the Indus, Ganges, and Brahmaputra basins.
Although the Mekong originates on the Tibetan Plateau and is the source of water for the populations of Cambodia, Laos, Thailand, and Vietnam, glaciers are a small component of water resources in the Mekong (Figure 1.4). The Yangtze and Yellow Rivers, which provide water for large parts of China, also originate on the Plateau and have relatively small glacial coverage (Figure 1.4). Because the Mekong, Yangtze, and Yellow River basins contain a relatively small amount of glacier area, it follows that discharge into these rivers results from snowmelt and rainfall. As discussed in Chapter 2, in most basins, the contribution of rain far outweighs the contributions of snowmelt (e.g., Andermann et al., 2012). These three rivers are located in the eastern part of the HKH region, where annual precipitation is dominated by the summer monsoon (Bolch et al., 2012). On the basis of these considerations, discharge into the Mekong, Yangtze, and Yellow Rivers is more influenced by the monsoons, and in the future, climate change effects on the monsoon will play a greater role than any changes in the glaciers.
It is common to refer to the Tsangpo/Brahmaputra to indicate that the upstream portion of the river on
FIGURE 1.4 Glacier area and percentage of total HKH glaciated area in each of the region’s river basins. Only the Indus, Ganges, Brahmaputra, and interior basins of the Tibetan Plateau contain more than 5 percent of the region’s glacier area. SOURCE: ICIMOD (2011b).