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The Upper Indus Basin (UIB), situated in the Himalaya-Karakoram-Hindukush (HKH) mountain ranges, is the major contributor to the supply of water for irrigation in Pakistan. Improved management of downstream water resources requires studying and comparing spatiotemporal changes in the snow cover and hydrological behavior of the river basins located in the HKH region. This study explored in detail the recent changes that have occurred in the Gilgit River basin (12,656 km(2); western sub-basin of UIB), which is characterized by a mean catchment elevation of 4250 m above sea level (m ASL). The basin's snow cover was monitored through the snow products provided by the MODIS satellite sensor, while analysis of its hydrological regime was supported by hydrological and climatic data recorded at different altitudes. The Gilgit basin findings were compared to those previously obtained for the lower-altitude Astore basin (mean catchment elevation = 4100 m ASL) and the higher-altitude Hunza basin (mean catchment elevation = 4650 m ASL). These three catchments were selected because of their different glacier coverage, contrasting area distribution at high altitudes and significant impact on the Upper Indus River flow. Almost 7, 5 and 33 % of the area of the Gilgit, Astore and Hunza basins, respectively, are situated above 5000 m ASL, and approximately 8, 6 and 25 %, respectively, are covered by glaciers. The UIB region was found to follow a stable or slightly increasing trend in snow coverage and had a discharge dominated by snow and glacier melt in its western (Hindukush-Karakoram), southern (Western-Himalaya) and northern (Central-Karakoram) sub-basins.

International audience; A large proportion of Pakistan's irrigation water supply is drawn from the Upper Indus River Basin (UIB) situated in the Himalaya-Karakoram-Hindukush (HKH) ranges. More than half of the annual flow in the UIB is contributed by five of its high-altitude snow and glacier-fed sub-basins including the Astore (Western Himalaya - southern part of the UIB), Gilgit (Hindukush - western part of the UIB) and Hunza (Central Karakoram - northern part of the UIB) River basins. Studying the snow cover, its spatio-temporal evolution and the hydrological response of these sub-basins is important so as to better manage water resources. This study compares data from the Astore, Gilgit and Hunza River basins (mean catchment elevation, 4100, 4250 and 4650 m ASL, respectively), obtained using MODIS satellite snow cover images. The hydrological regime of these sub-catchments was analyzed using hydrological and climate data available at different altitudes from the basin areas. The results suggest that the UIB is a region undergoing a stable or slightly increasing trend of snow cover in the southern (Western Himalayas), western (Hindukush) and northern (Central Karakoram) parts. Discharge from the UIB is a combination of snow and glacier melt with rainfall-runoff in the southern part, but snow and glacier melt is dominant in the northern and western parts of the catchment. Despite similar snow cover trends (stable or slightly increasing), different river flow trends (increasing in Astore and Gilgit, decreasing in Hunza) suggest that a sub-catchment level study of the UIB is needed to understand thoroughly its hydrological behavior for better flood forecasting and water resources management and to quantify how the system is being forced by changing climate.

In this study we analyze the temperature and precipitation data collected by sixteen in-situ stations located in the high-elevated regions of northern Pakistan to provide a climatic characterization of the Karakoram mountains. We focus our attention on the analysis of the precipitation annual cycle at the various stations and on the investigation of the vertical variability of both precipitation and temperature, averaged over the Upper Indus Basin (UIB) area. The precipitation annual cycle at the individual stations generally shows higher precipitation amounts in winter (December to April) than in summer (June to September), confirming that northern Pakistan is not under the prevailing influence of the Indian monsoon. The spatially-averaged temperature and precipitation vertical gradients show that the temperature lapse rate is consistent with the moist adiabatic lapse rate of the atmosphere. The vertical precipitation gradient indicates an increase with elevation until about 3,000 m and then a decrease that can be attributed to the strong underestimate of solid precipitation by rain gauges at high-altitudes.