BPR at Nuxia essentially equally contributed by precipitation, melt water and groundwater, while the other tributaries are fed mainly check details by rain (Table 2; Guan and Chen, 1980 and Liu, 1999). On average, surface runoff increases toward the lower reaches of BPR (Guan and Chen, 1980).

During 1956–2000, the Nugesha, Yangcun and Nuxia stations located in the main tributary showed slightly decreasing annual flow while the Lazi station located in the source region exhibited slightly increasing annual flow (Table 3; Huang et al., 2007 and Li et al., 2010). The Lhasa River, a tributary of BPR, presented slightly increasing trends in annual flow during 1956–2003 (Table 3; Lin et al., 2007). In SWR, rainfall is the major contributor to the annual flow (Table 2; Fan and He, 2012 and Zhang et al., 2013b) although in the upper reach above station Jiayuqiao, melt water is also SB431542 order important and accounts for 25% of the annual flow (Zhang et al., 2013b). At Jiayuqiao, both the annual and the monthly streamflow showed increasing trends during 1980–2000 except for

June and July and the increasing trends were statistically significant for January–April (Table 3; Yao et al., 2012b). In the lower reach between Jiayuqiao and Daojieba, the annual streamflow also increased during 1958–2000 (Table 3), and the increases in the low flow season (November–February) were statistically significant (Yao et al., 2012b). In general, streamflow of the Pacific Ocean and the Indian Ocean oriented rivers is rainfall dominated but for the headwaters of these rivers melt water is more important, for example, the Tuotuo River of the YTR (Table 2). It appears that the melt water contribution diminishes as the

basins expand from the source region to the Thiamet G lower reaches for both types of rivers. The streamflow changes at various locations along the rivers are different due to the differences in the major contributions to the streamflow and the dominant acting factors such as temperature and precipitation. Historically, all tributaries in TRB flowed to the Tarim River, the main branch. The major tributaries of the Tarim River included the Yarkant, Hotan and Aksu Rivers, which contribute about 3.6%, 23.2% and 73.2%, respectively, to the Tarim River (Chen and Xu, 2004). The Yarkant River used to be the headwater of the Tarim River but it has now lost the connection to the Tarim River except in the extreme flooding season. In TRB, the June–September flow accounts for 72–80% of the annual total (Chen et al., 2003). The major contribution to streamflow in TRB is from melt water, which accounts for approximately half of the annual total (Table 2; Fu et al., 2008), although this number varies among the studies. The lower TRB is desert where precipitation is very limited.