Snow-Glacier Dynamics and Alpine Hydrological Processes in Hindukush-Karakoram and Himalayas Region of Pakistan under Future Climate Projections

Abstract

Snow-Glacier Dynamics and Alpine Hydrological Processes in Hindukush-Karakoram and Himalayas Region of Pakistan under Future Climate ProjectionsPakistan’s economy predominately relies on the agricultural sector that is thrived on the water supplied by the Upper Indus Basin (UIB) originating from Hindukush Karakoram-Himalaya (HKH) range. Snow and glacier melt in the high altitude remotemountainous river basins is accelerating due to warming trends. For efficientmanagement and rational use of freshwater resources, investigating snow and glaciercover dynamics and their relation with the hydrology of the UIB is a prerequisite. This study concentrated on the snow cover and glacier dynamics, snowmelt runoff modeling, flood assessment, and mapping, and estimation of the hydro-climatological trends in the Chitral (Hindukush range), Hunza (Karakoram range), and Astore (Himalaya region) sub-basins of UIB. Digital Elevation Model (DEM) data obtained from Advanced Land Observation Satellite (ALOS) was used for the delineation of basins, different elevation zones, and hypsometric study. Moderate Resolution Imaging Spectro-radiometer (MODIS) snow product (MOD10A2) was utilized for estimating basin-wide (BW) and zone-wise (ZW) Snow Cover Area (SCA) over 2000–2016 data period for all the basins. Glacier dynamics were studied in terms of Equilibrium Line Altitude (ELA) and geodetic mass balance of fifteen representative glaciers having area >5 km2 each, situated in the study area using LANDSAT satellite images and ASTER DEMs (DEMs) during years 2000 and 2018. Snowmelt Runoff Model (SRM) furnished with snow cover maps and hydro-meteorological data (temperature, precipitation, and river discharge) was applied to simulate the daily discharge from the study area during the 2000‒2004 data period. SRM was calibrated and validated for the period of 2000–2001 and 2002–2004, respectively, using basin-wide as well as zone-wise approaches. The calibrated model was then applied to simulate the snowmelt runoff under Representative Concentration Pathways (RCP) climate scenarios of the mid and late 21st century. Hydrological Engineering Center River Analysis System (HEC-RAS) model was then employed to assess and map the flood-prone areas in selected portions of the studied basins using the simulated flow by SRM under RCP scenarios, DEMs, and geometries of study areas. Finally, the trends in SCA, mean annual temperature, mean total precipitation, and discharge of the three basins and correlation among these variables were assessed using various statistical methods. The results showed that the mean annual SCA varies between ~20–91%, ~37–81%, and ~7–91% in the Chitral, Hunza, and Astore basins, respectively. Maximum SCA was found to be above 5500 m asl elevation zones, sometimes reaching 100% of the zonal area. A slightly increasing or consistent trend of SCA was observed in the studied basins over the studied period. Glacier dynamics study indicated that the ELA of all the studied glaciers except two are shifted upward (showing s decrease in accumulation area), while the mass balance is found to be heterogeneous across the basins over the study period. The results of snowmelt runoff modeling imply that the SRM has efficiently simulated the discharge with Nash-Sutcliffe coefficient of 0.87 (0.84), 0.83 (0.88), and 0.89 (0.78) for BW (ZW) application in the Chitral, Hunza, and Astore basins, respectively. Mean annual discharge was estimated to increase by ~14–19%, ~14–90%, and 11–58% in the Chitral, Hunza, and Astore basins, respectively, for the mid and late-21st century RCP scenarios. Mean summer discharge was expected to increase between 10‒60% under RCP scenarios in the study areas. Discharge simulated under the RCP 8.5 scenario indicated severe flooding inundating an area of ~66%, ~86%, ~37% (mid-21st century) and, ~72%, ~93%, ~59% (late-21st century) for the studied reaches of Chitral, Hunza, and Astore River basins, respectively. A significant or slight increasing or decreasing trend was found in the mean annual temperature, mean total precipitation, and mean discharge of the studied basins. The snow cover in the studied basins was found to be strongly influenced by temperature seasonality, in turn affecting the discharge. This study may be a good contribution for understanding snow and glacier dynamics in HKH, and the factors that influence it, and their interaction with the environment. This study may also help water resource managers to plan and ensure freshwater availability in the country and to reduce the flood risks.