Observed and Predicted Climate Change Impact on Water Resources of the Upper Indus Basin: English
Climate change has implications for water resources across the World by increasing temperature, shifting precipitation patterns and altering the timing of snowfall/snowmelt, that can lead to seasonal variations in river flows. The water resources of the Upper Indus Basin (UIB) are highly dependent on the winter westerly disturbances (WWD) and summer monsoon systems. However, the impacts of change in this complex climate system vary spatially and temporally across the UIB, making it difficult to assess current and predict future impacts on water resources for countries like Pakistan that rely heavily on water supplied by the Indus. This project consists of two parts. In the first part, an investigation is conducted to explore long-term trends in climate change and its impact on water resources (river flows) across the sub-basins of the UIB. Analysis of long-term trends in temperature from satellite-based climate observations showed warming at high altitudes and summer cooling in low altitude sub-basins. River flows were highly correlated with temperature in high altitude sub-basins and with precipitation in low-altitude sub-basins. In low altitude sub-basins, a significant decrease in river flow was observed, possibly as a result of enhanced vegetation growth (determined through NDVI analysis) by spring warming leading to evaporative summer cooling. Regionally, river flow increased in the eastern part of the Karakoram but decreased in the west, illustrating spatial variability in river flow trends which was further investigated using Snow Water Equivalent (SWE) and Water Balance (WB) data. Spatially heterogeneous trends in SWE and WB were observed across the Karakoram. In the second part of the research, the impact of climate and land use/ land cover (LULC) change on water resources was examined by using the SWAT hydrological model with inputs from downscaled Global Climate Models (GCMs) and different IPCC emission scenarios, namely RCP4.5 and RCP8.5. The calibrated and validated SWAT model was run with downscaled GCM data for near future (2020-2050) and end of the century (1970-2100) scenarios relative to a baseline period (1974-2004). All GCMs projected an increase in temperature over the UIB, whereas there was a lack of agreement on future precipitation patterns between GCMs under both emission and future scenarios. Overall, a spatial variation in water yield was noted across the region with some regions experiencing an increase, and others a decrease, particularly in the end of the century scenario. A shift in the timing of peak seasonal flows (by one month) was projected in each sub-basin. The impact of LULC change scenarios was much smaller compared to climate change scenarios on water resources of the UIB. Overall, climate change will result in an increase in water yield in near future and early shifts in timing of peak flows, which could have implications for agricultural activities and water supply and management for the greater part of Pakistan given the country’s reliance on the Indus in the 21st century.
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