Impacts of Climate Change on River Flows in the Upper Indus Basin and Its Subbasins

Abstract The upper Indus river basin (UIB) has a cold climate and generates vital runoff annually. This runoff is very important for sustainable water supply and agriculture in the region. Runoff in UIB consists of rainfall, snow and glacier melt. Winter precipitation in the basin is essential for the replenishment of glaciers which is the most dominant runoff source. Climate change may alter the runoff generation in the basin and affect the availability of water for consumption. This study employs a hydrologic model and a fine resolution MRI-AGCM (0.1875°) to quantify the impacts of climate change on river flows in UIB and its sub-basins. The simulations of river flows have shown satisfactory results when compared with observed ones. Furthermore, simulated snow-cover is compared with estimated snow-cover by MODIS and has shown good agreement. According to simulation results glaciers alone contribute two-third in the annual river flows at UIB while rainfall and snow contributes 19 and 11% respectively. Future (2075-2099) temperature will increase in every season across the UIB, highest increase is projected to take place in September-October with approximately 8 °C. While, on annual basis the temperature will increase by 5 °C. Likewise, precipitation will increase every month across UIB, specifically the increase in July-August period is very significant. Albeit the precipitation increase is highly variable on spatial scale i.e. decreasing/increasing at same time in different regions. This variable behavior of future precipitation will result in verities of hydrographs in UIB and its sub-basins. Overall in UIB the annual river flows will decrease by 16% with significant seasonal variations. Summer flows will decrease and spring flows will increase because of glacier retreat and higher precipitation. Sub-basins’ response is mixed with increasing and decreasing because of different topography, climate and other factors. These changes necessitate a more holistic approach in mitigating the changes in the water availability.