INDUS BASIN DEPENDENCY ON MOUNTAIN WATERS: ASSESSMENT OF FUTURE WATER AVAILABILITY AND ITS EFFECT ON LARGE RESERVOIRS PROPOSED UNDER PAKISTAN WATER VISION 2025.

A.N. LAGHARI, H. U. ABBASI, A. A. MEMON, S.R. SOOMO

Abstract


The  mountainous  region of Upper Indus Basin is critical water supply source  for Indus River System and thus for Pakistan. The future water availability scene for proposed reservoirs are investigated through the  potential impacts of climatic change  on flow regime of Hunza basin under hypothetically generated climate change scenarios simulated through the application of the semi-distributed hydrological model PREVAH  over a period of 10 years and consequent impact upon flow regime of main Indus River. The adopted climate scenarios ranging from 1 to 4°C temperature change are based on ensemble of 9 global model predictions for the studied region in 21st century. Under all adopted scenarios, total stream flow produces an early response along with a change in their runoff distribution. The early and extended ablation period for snow and ice melt have significantly enhanced water availability in main Indus River. The flow pattern of Indus River and its tributary Hunza shows identical percentage change in their monthly contribution  to respective annual flow volumes, as major contribution in both rivers comes from snow and ice melt runoff. The regression coefficient was above 90%. The relationship was used to estimate the water availability in main Indus River. An increase of 1 to 4°C have resulted in net increase of about 2.35 to 11.84 BCM in winter flows and 15.51 to 58.71 BCM in summer flows, while 17.86 to 70.56 BCM increase were recorded in mean annual flows. The mean annual figure of Indus River, even at 1°C shows sufficient water availability  for proposed reservoirs. Based on current Indus River data analysis and future water availability scene under warmed scenarios, the government’s decision to develop new reservoirs as to meet future demands through tapping part of 42 BCM unutilized water flowing to Arabian Sea, seems justifiable and also viable in changing climate. In nutshell, the increased snow and glacier melt runoff and resulting massive increase in summer flows justifies the construction of new reservoirs, as it will not only reduce the threat of floods but enhance the present capacity of regulating and utilizing surpluses water for crop irrigation in much needed times particularly during low flow period of the winter and early and late summer season.


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