Abstract

The Soil andWater Assessment Tool (SWAT) model combined with a temperature index and elevation band algorithm was applied to the Hunza watershed, where snow and glacier-melt are the major contributor to river flow. This study’s uniqueness is its use of a snow melt algorithm (temperature index with elevation bands) combined with the SWAT, applied to evaluate the performance of the SWAT model in the highly snow and glacier covered watershed of the Upper Indus Basin in response to climate change on future streamflow volume at the outlet of the Hunza watershed, and its contribution to the Indus River System in both space and time, despite its limitation; it is not designed to cover the watershed of heterogeneous mountains. The model was calibrated for the years 1998–2004 and validated for the years 2008–2010. The model performance is evaluated using the four recommended statistical coefficients with uncertainty analysis (p-factor and r-factor). Simulations generated good calibration and validation results for the daily flow gauge. The model efficiency was evaluated, and a strong relationship was observed between the simulated and observed flows. The model results give a coefficient of determination (R2) of 0.82 and a Nash–Sutcliffe Efficiency index (NS) of 0.80 for the daily flow with values of p-factor (79%) and r-factor (76%). The SWAT model was also used to evaluate climate change impact on hydrological regimes, the target watershed with three GCMs (General Circulation Model) of the IPCC fifth report for 2030–2059 and 2070–2099, using 1980–2010 as the control period. Overall, temperature (1.39 C to 6.58 C) and precipitation (31%) indicated increased variability at the end of the century with increasing river flow (5%–10%); in particular, the analysis showed smaller absolute changes in the hydrology of the study area towards the end of the century. The results revealed that the calibrated model was more sensitive towards temperature and precipitation, snow-melt parameters and Curve Number (CN2). The SWAT results also provided reliable information for the daily runoff from the sub-basin watersheds responding to changing climatic conditions. SWAT can thus be used to devise effective strategies for future sustainable water management in the region, while combating vulnerabilities against floods and water storage in downstream water reservoirs such as the Diamer-Basha dam.

Highlights

  • Mountains play an important role in supplying water for downstream areas

  • About one-sixth of the global population depends on these freshwater sources i.e., glacier, ice and snow [1], which provide a lifeline for the people who inhabit the downstream areas [2]

  • The Hunza watershed with an area of 13,567.23 km2 is situated in the Upper Indus Basin (UIB) area, Pakistan, in the north bordering with China and Afghanistan in the Karakoram mountain range (Figure 1)

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Summary

Introduction

Mountains play an important role in supplying water for downstream areas. The Himalayan. Very little is known about the performance of the SWAT (Soil and Water Assessment Tool) model in a typical highly snow and glacier covered dry-temperate mountainous watershed, which provides a significant amount of water supply to the Indus River. Not a single study has been conducted yet using a complex, physical measurement based distributed hydrological model to assess the contribution of snow and glacier melts to IRS from this particular (Hunza) sub-basin. This study was conducted to evaluate the performance of the SWAT model in a highly snow and glaciated watershed, in response to changing climate and its impact on streamflow volumes as well as in the long run, at the outlet of the Hunza watershed, and its contribution to the Indus. River System, which may help the local water management authorities devise effective strategies for sustainable water management in the region

Study Area
SWAT Data
Model Calibration and Validation
Results and Discussion
Futuredischarge
Conclusions
Full Text
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