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