2 | STUDY AREA

As shown in Figure 1, the Indus river basin (24°-37°N, 66°-82°E), located in the subtropical arid zone with semiarid climate, is a typical outflow basin. It covers ~1.22 × 106km2 of total area (Dahri et al., 2016; Immerzeel, Ludovicus & Bierkens, 2010), and includes ~1.72 × 105km2 area lies upstream Tarbela dam situated at the Besham city of northern Pakistan, which is defined as the UIB (31°-37°N, 72°-82°E) with the elevations ranging from 200 to 8600 m, UIB has mean annual precipitation around 815 mm, and an annual temperature is estimated between -10℃ and 22℃. An adopted watershed division scheme in this study was derived from SRTM DEM (90 m) (Khan, Richards, Parker, McRobie & Mukhopadhyay, 2014), there is no definite boundary among the HKKH ranges. The UIB is generally divided into eight drainage units by river mainstream and its tributaries, Gilgit and UIB_Downstream (UIB_D) sub-watersheds draining the Hindukush range, the Karakoram range comprises Hunza, Shigar, and Shyok sub-watersheds, and the Western Himalaya range is composed of Astore, Kharmong, and Shiquanhe sub-watersheds. According to the latest research and Pakistan glacier inventory (PGI), 12% part of the UIB area was glaciated, the cumulative area of 11,711 glaciers is 1.78 × 104km2approximately, and 70% of glaciers are distributed in high altitude sub-basins (i.e., Hunza, Shigar, and Shyok) (Bajracharya & Basanta, 2011; SUPARCO & ITPCAS, 2015).
FIGURE 1 Location of (a) the Indus river basin and (b) the UIB sub-basins