*2.1. Study Area*

In the current study, the climate change model selection procedure was carried out for the UIB, which is spread over the Hindu-Kush, Karakorum and Himalayan ranges, and feeds the largest canal system in the world (Figure 1). This river basin is very important due to two main reasons: first, the irrigated agriculture of Pakistan overwhelmingly depends on the inputs from this river basin; and second, the region is probably a climate change hot-spot [8,9], with an extremely uncertain future hydro-climatology. The future scenario data from the selected models are intended to be used, after downscaling and bias correction, as input to the SWAT hydrological model [10] for quantifying possible climate change impacts on the hydrological dynamics of the basin.

Climatic variables are usually strongly influenced by topographic altitude. Thus, the northern valley floors of the UIB are arid and warm, with an annual precipitation of only 100–200 mm. These totals increase to 600 mm at 4400 m altitude, and glaciological studies suggest annual accumulation rates of 1500–2000 mm at height of 5500 m [11]. The UIB draws more than 50% of its water from melting of seasonal and permanent snow cover in the Himalaya, Karakoram and the Hindu Kush (HKH) mountains [5,12–15]. A rise in temperature in the UIB will, therefore, result in elevated melt rates with huge impacts on the timing and magnitude of the generated flows. This will not only lead to a higher average stream flow, but also to an increase in the occurrence and magnitude of extremes, especially during high-precipitation events [16]. There is also the possibility that the peak flows may shift to earlier months or other seasons, with a rise in temperature [5] in the UIB.

**Figure 1.** Upper Indus Basin (UIB): Main catchments, meteorological stations, streams and tributaries.

All these facts make UIB a very sensitive region to possible climate change, and even, according to some [17], a climate-change "hotspot". However, despite the necessity of intensified investigations on different aspects of climate change and its possible implications, the task is hindered by the harshness of the environment and the unavailability of representative data. The climatic data available in the UIB lacks suitable coverage, since the in situ meteorological observations in the UIB are sparse and mostly taken at valley stations. Furthermore, the complex orography of the UIB region also affects the amounts, spatial patterns and seasonality of the precipitation. Therefore, neither the sparsely observed station data and gridded data products based on them, nor the sensors-based data, fully represent the precipitation regime of the region [6].
