HKH hydrological projections

Introduction:

The increasing rate of warming is significantly higher in the Hindu Kush Himalayan (HKH) region than the global average in the past century (Duet al 2004). The warming influence is much higher in the Eastern Himalayas compared with the Greater Himalayan region (Sheikh et al 2014). These temperature variations can have a potential impact on water resources of the UIB and the dependent downstream irrigation demand areas, which are of great concern. In HKH region snow melt and glacier melt yield collectively account more than 70% of UIB stream-flows. Most part of HKH lies above 5,000 meters and contains the second-highest peak of K2 mountain i.e. above 8,000meter. Most of the annual precipitation in UIB falls during winter and spring (December-April, DJFMA) due to western disturbances that is eastward propagating synoptic systems embedded into westerly flow (Madhura et al 2014). Whereas the summer monsoon and local circulations only accounts 1/3 of annual precipitation (Young and Hewitt 1990). The climatic conditions of UIB are different from other regions of the country; as the monsoon circulation weakens towards northwest in UIB where high mountains of the Himalaya decrease the effect of monsoon circulation. Although the lower elevation stations do not monitor very high precipitation during both the winter and summer, but in contrast high altitude stations usually recorded much higher precipitation. Previous studies suggested very significant precipitation gradient at high altitudes and even at some parts (>5000 meters) of the basin the annual precipitation exceeds 2000 mm (Mukhopadhyay and Khan 2014). Fowler and Archer (2006), reported an increasing trend in both precipitation and temperature during winter while a cooling in summer temperatures over the past century. The average river flow to Tarbela reservoir at Besham Qila reaches 2425 cumecs (cubic meters per second) with the variation between 80% to 130 % from the mean. There are eight meteorological observatories (Kakul, Garidupatta, Balakot, Astor, Bunji, Skardu, Gilgit, and Gupis) in the study area.

Hydrological projections:

Total riverflow is continuously increasing over time in the Upper Indus River. The increasing rate of riverflow in both RCPs is enhanced during thefirst two time slices (2006–2035 and 2041–2070), while it is smaller and not in the same ratio during the last time slice (2071–2100) in RCP8.5 and it even decreases for RCP4.5 when compared with 2041–2070. In the summer for RCP4.5, the increase is 24% during 2006–2035, 32% during 2041–2070, and 26% during 2071–2100. In RCP8.5, the percentage increase is 23% during 2006–2035, 50% during 2041–2070, and 55% during 2072–2100. The results show that percent increase is higher in winter than summer in both scenarios. Maximum river flow occurring in summer shows that the highest riverflow in RCP8.5 is of 9720 cumecs for the period of 2006–2035, 11 837 cumecs for the period of 2041–2070, and 12 222 cumecs for the period of 2071–2100. In RCP4.5 the highest river flow in summer is 9783 cumecs for the period of 2006–2035, 10 428 cumecs for the period of 2041–2070, and 9954 cumecs for the period of 2071–2100. The projection for increased river flow was higher in RCP8.5 than RCP4.5, mainly due to a significant increase in temperatures.

GCISC References:

Gul C, Shaukat Ali. et al (2017): Using Landsat images to monitor changes in the snow-covered area of selected glaciers in northern Pakistan. Journal of Mountain Science (Accepted)

Khan, F., Pilz, J., & Shaukat Ali. (2017). Improved hydrological projections and reservoir management in the Upper Indus Basin under the changing climate. Water and Environment Journal.

Mountain Research Initiative EDW Working Group. Muhammad Zia ur Rahman Hashmi (2015). Elevation-dependent warming in mountain regions of the world. Nature Climate Change, 5(5), 424-430.

Shaukat Ali, Li, D., Congbin, F., & Khan, F. (2015). Twenty first century climatic and hydrological changes over Upper Indus Basin of Himalayan region of Pakistan. Environmental Research Letters, 10(1), 014007.