The upper Indus River basin has large masses of glaciers that supply meltwater in the summer. Water resources from the upper Indus River basin are crucial for human activities and ecosystems in Pakistan, but they are vulnerable to climate change. This study focuses on the impacts of climate change, particularly the effects of receding glaciers on the water resources in a catchment of the upper Indus river basin. This study predicts river flow using a hydrologic model coupled with temperature-index snow and glacier melt models forced by observed climate data. The basin is divided into seven elevation zones so that the melt components and rainfall-runoff were calculated at each elevation zone. Hydrologic modeling revealed that glaciers contributed one-third of the total flow while snowmelt melt contributed about 40%; rainfall contributed to the remaining flow. Some climate scenarios based on CMIP5 and CORDEX were employed to quantify the impacts of climate change on annual river flows. The glacier retreat in the mid and late centuries is also considered based on climate change scenarios. Future river flows, simulated by the hydrologic model, project significant changes in their quantity and timing. In the mid-century, river flows will increase because of higher precipitation and glacier melt. Simulations projected that until 2050, the overall river flows will increase by 11%, and no change in the shape of the hydrograph is expected. However, this increasing trend in river flows will reverse in the late century because glaciers will not have enough mass to sustain the glacier melt flow. The change will result in a 4.5% decrease in flow, and the timing of the monthly peak flow will shift from June to May. This earlier shift in the streamflow will make water management more difficult in the future, requiring inclusive approaches in water resource management.

1. [1] Q. U. Z. Chaudhry, “Climate change profile of Pakistan,” Asian Development Bank, 2017.
2. [2] C. Mcsweeney, M. New, and G. Lizcano, “UNDP Climate Change Country Profiles Pakistan,” United Nations Development Programme, 2012.
3. [3] W. W. Immerzeel, N. Wanders, A. F. Lutz, J. M. Shea, and M. F. P. Bierkens, “Reconciling high-altitude precipitation in the upper Indus basin with glacier mass balances and runoff,” Hydrol. Earth Syst. Sci., Vol.19, No.11, pp. 4673-4687, doi: 10.5194/hess-19-4673-2015, 2015.
4. [4] B. Mukhopadhyay, A. Khan, and R. Gautam, “Rising and falling river flows: contrasting signals of climate change and glacier mass balance from the eastern and western Karakoram,” Hydrol. Sci. J., Vol.60, No.12, pp. 2062-2085, doi: 10.1080/02626667.2014.947291, 2015.
5. [5] A. F. Lutz, W. W. Immerzeel, P. D. A. Kraaijenbrink, A. B. Shrestha, and M. F. P. Bierkens, “Climate change impacts on the upper indus hydrology: Sources, shifts and extremes,” PLoS One, doi: 10.1371/journal.pone.0165630, 2016.
6. [6] P. D. A. Kraaijenbrink, M. F. P. Bierkens, A. F. Lutz, and W. W. Immerzeel, “Impact of a global temperature rise of 1.5 degrees Celsius on Asia’s glaciers,” Nature, Vol.549, pp. 257-260, doi: 10.1038/nature23878, 2017.
7. [7] A. F. Lutz, W. W. Immerzeel, A. B. Shrestha, and M. F. P. Bierkens, “Consistent increase in High Asia’s runoff due to increasing glacier melt and precipitation,” Nat. Clim. Chang., Vol.4, pp. 587-591, doi: 10.1038/nclimate2237, 2014.
8. [8] M. Huss and R. Hock, “A new model for global glacier change and sea-level rise,” Front. Earth Sci., doi: 10.3389/feart.2015.00054, 2015.
9. [9] D. R. Rounce, R. Hock, and D. E. Shean, “Glacier Mass Change in High Mountain Asia Through 2100 Using the Open-Source Python Glacier Evolution Model (PyGEM),” Front. Earth Sci., doi: 10.3389/feart.2019.00331, 2020.
10. [10] S. ul Hasson, “Future Water Availability from Hindukush-Karakoram-Himalaya upper Indus Basin under Conflicting Climate Change Scenarios,” Climate, Vol.4, No.3, Article No.40, doi: 10.3390/cli4030040, 2016.
11. [11] A. Soncini et al., “Future Hydrological Regimes in the Upper Indus Basin: A Case Study from a High-Altitude Glacierized Catchment,” J. Hydrometeorol., Vol.16, No.1, pp. 306-326, doi: 10.1175/JHM-D-14-0043.1, 2015.
12. [12] R. Hock, “Temperature index melt modelling in mountain areas,” J. Hydrol., Vol.282, No.1-4, pp. 104-115, doi: 10.1016/S0022-1694(03)00257-9, 2003.
13. [13] A. A. Tahir, P. Chevallier, Y. Arnaud, L. Neppel, and B. Ahmad, “Modeling snowmelt-runoff under climate scenarios in the Hunza River basin, Karakoram Range, Northern Pakistan,” J. Hydrol., Vol.409, No.1, pp. 104-117, doi: 10.1016/j.jhydrol.2011.08.035, 2011.
14. [14] T. Sayama, G. Ozawa, T. Kawakami, S. Nabesaka, and K. Fukami, “Rainfall–runoff–inundation analysis of the 2010 Pakistan flood in the Kabul River basin,” Hydrol. Sci. J., Vol.57, No.2, pp. 298-312, doi: 10.1080/02626667.2011.644245, 2012.
15. [15] D. K. Hall and G. A. Riggs, “MODIS/Terra Snow Cover 8-Day L3 Global 500m SIN Grid, Version 6,” NASA National Snow and Ice Data Center Distributed Active Archive Center, 2001, https://nsidc.org/data/MOD10A2 [accessed March 15, 2019]
16. [16] ICIMOD, “Clean Ice and Debris covered glaciers of HKH Region,” 2011, http://apps.geoportal.icimod.org/hkhglacier [accessed March 16, 2019]
17. [17] B. Lehner, K. Verdin, and A. Jarvis, “HydroSHEDS: Technical Documentation,” 2006, http://hydrosheds.cr.usgs.gov/ [accessed December 17, 2018]
18. [18] A. Valéry, V. Andréassian, and C. Perrin, “Regionalization of precipitation and air temperature over high-altitude catchments – learning from outliers,” Hydrol. Sci. J., Vol.55, No.6, pp. 928-940, doi: 10.1080/02626667.2010.504676, 2010.
19. [19] A. J. Khan and M. Koch, “Correction and informed regionalization of precipitation data in a high mountainous region (Upper Indus Basin) and its effect on SWAT-modelled discharge,” Water, Vol.10 No.11, doi: 10.3390/w10111557, 2018.
20. [20] Z. H. Dahri et al., “Adjustment of measurement errors to reconcile precipitation distribution in the high-altitude Indus basin,” Int. J. Climatol., Vol.38, No.10, pp. 3842-3860, doi: 10.1002/joc.5539, 2018.
21. [21] A. Valéry, V. Andréassian, and C. Perrin, “‘As simple as possible but not simpler’: What is useful in a temperature-based snow-accounting routine? Part 2 – Sensitivity analysis of the Cemaneige snow accounting routine on 380 catchments,” J. Hydrol., Vol.517, pp. 1176-1187, doi: 10.1016/j.jhydrol.2014.04.058, 2014.
22. [22] W. Terink, A. F. Lutz, G. W. H. Simons, W. W. Immerzeel, and P. Droogers, “SPHY v2.0: Spatial Processes in HYdrology,” Geosci. Model Dev., Vol.8, No.7, pp. 2009-2034, doi: 10.5194/gmd-8-2009-2015, 2015.
23. [23] T. Sayama, “RRI User Manual,” 2015.
24. [24] P. Wester, A. Mishra, A. Mukherji, and A. B. Shrestha, “The Hindu Kush Himalaya Assessment,” Springer International Publishing, 2019.
25. [25] M. Huss, G. Jouvet, D. Farinotti, and A. Bauder, “Future high-mountain hydrology: A new parameterization of glacier retreat,” Hydrol. Earth Syst. Sci., Vol.14, No.5, pp. 815-829, doi: 10.5194/hess-14-815-2010, 2010.
26. [26] S. Hasson, V. Lucarini, M. R. Khan, M. Petitta, T. Bolch, and G. Gioli, “Early 21st century snow cover state over the western river basins of the Indus River system,” Hydrol. Earth Syst. Sci., Vol.18, doi: 10.5194/hess-18-4077-2014, 2014.
27. [27] J. E. Nash and J. V. Sutcliffe, “River flow forecasting through conceptual models part I – A discussion of principles,” J. Hydrol., Vol.10, No.3, pp. 282-290, doi: 10.1016/0022-1694(70)90255-6, 1970.
28. [28] M. Iqbal, G. Akhter, A. Ashraf, and S. Ayub, “Snowmelt runoff assessment and prediction under variable climate and glacier cover scenarios in Astore River Basin, Western Himalayas,” Arab. J. Geosci., Vol.11, Article No.568, doi: 10.1007/s12517-018-3923-6, 2018.
29. [29] H. Hayat, T. A. Akbar, A. A. Tahir, Q. K. Hassan, A. Dewan, and M. Irshad, “Simulating Current and Future River-Flows in the Karakoram and Himalayan Regions of Pakistan Using Snowmelt-Runoff Model and RCP Scenarios,” Water, Vol.11, No.4, Article No.761, doi: 10.3390/w11040761, 2019.