Robust Stream flow Predictions using Parametric Sensitivity Analysis of Multiple Hydrological Models in Hindu kush Karakoram-Himalayas (HKH) Region

Abstract

The complex snow and glacier (cryosphere) dynamics over “third pole” mountainous regions of the Karakoram-Hindukush-Himalayas (HKH) makes this region challenging for the accurate hydrological predictions, therefore, understanding with the hydrology is still poorly studied, particularly to changing climate. The main study objectives includes to investigate the climate change impact on major components of hydrology (precipitation-runoff, snow- and glacier-runoff, evapotranspiration and inter-annual change in streamflows) over the Hunza-, Gilgit- and Astore River basin, located in HKH. To achieve this, we tested three different hydrological models (snowmelt runoff (SRM), HEC-HMS and HBV) over high-altitude snow- and glacier-covered river basins, subsequently integrated with the climate projections simulated from Regional Climate Models (RCMs) developed at spatial resolution i.e. fine under Coordinated Regional Climate Downscaling Experiment-South Asia (CORDEX-SA) experiments. Results depicted that the SRM is more capable to reproduce daily streamflow over a high-altitude snow- and glacier-covered basins as compare to HEC-HMS and HBV. Further, the basin-wide ensembles of RCM simulations exhibited an increase in mean annual precipitation by 20% (131mm), 23% (101 mm) and 16% (48 mm) over Astore-, Hunza- and Gilgit-River basin, respectively, under RCP8.5, during 2090s. The zone-wise change exhibited decrease in intensity of precipitation rise with increase in altitude. The mean temperature rise showed a maximum basin-wide increase during monsoon season by 4.34 ᴼC, 4.18 ᴼC and 4.37 ᴼC over Astore-, Hunza- and Gilgit-River basin, respectively, during 2090s for RCP8.5. Further, in response to rise in precipitation and temperature, the SRM simulations provides a significant rise in snow- glacier-melt runoff (49%, 42% and 46% for SRM) and precipitation runoff (23.8%, 15.7% and 27% for HEC-HMS) in Hunza-, Gilgit- and Astore River basin, respectively, during 2090s under RCP8.5. The streamflow projections for SRM xiv showed a substantial shift in hydrological regime of the study basins with increase in streamflow by 369 m3 /s (168.4%), 216.5 m3 /s (74.8%) and 131.8 m3 /s (82%) in Hunza-, Gilgit- and Astore River basin, respectively, under RCP8.5 for the season of pre-monsoon of 2090s. Additionally, stream flow projections for SRM during monsoon season of 2090s exhibited a significant decrease by -73.2 m3 /s (-13.9%) and -45.4 m3 /s (23.4%) in Hunza- and Astore-River basin, respectively, for RCP8.5. Overall, these projections show the season of monsoon and pre-monsoon are expected to utmost influenced by the climate change, consequently, alteration in glacier- and snow-accumulation and then melt down, thereby change in hydrological regime of the river basins located in HKH