Hydro Climatological Studies of Gilgit River Basin Pakistan

Abstract

The hydro-climatological inequalities in Gilgit drainage basin of Upper Indus basin are less technically understood due to various geography, approachability of the region and larger variations in climatic conditions. Glacier change examination and the extraction of catchments at multiple gauges are important tasks in undertaking the drainage basin management studies and are important components of two branches of hydrology viz., hydro-meteorology and snow-hydrology. Satellite remote sensing (SRS) and geographical information systems (GIS) provide a very useful method to study the watersheds. In view of the facts, watershed/ natural resources management in the Gilgit river basin, application of geospatial techniques to various elevation datasets is required in order to obtain more accurate results using these elevation datasets. To achieve this goal, the topographic feature extraction has been studied in the catchment of Gilgit River using different Digital Elevation Models (DEMs) viz., Shuttle Radar Topography Mission (SRTM), Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) and Global Digital Elevation Model of 30 arc sec approximately 1KM (GTOPO30). Several small watersheds for the Phakor, Karamber, East Gammu, Bhort and Bad-e-Swat glaciers were delineated for the basin definition. The delineated watersheds have been visually analyzed against the optical Landsat 8 OLI imagery for mountainous ridge matching. The results revealed that, SRTM 30m (radar-based) exhibited more accuracy among these DEMs because of its precise delineation in the Gilgit sub-basin. However, it is appropriate to say that computed area from all three DEMs generally shows close agreement. Temporal analysis of Bhort, Bad-e-Swat, East Gammu, Karamber and Phakor Glaciers has been done using object-based classification. Landsat Thermal Mapper, Enhanced Thermal Mapper+ and Operation Land Imagers satellite data for duration of 30 years (1988, 1994, 1999, 2014 and 2018) are used for this study. Thus comparison of glacier temporal extent has been made. It is observed that at large the glaciers in the Gilgit watershed are rather stable. The little variability of glaciers is due to their geographic condition, altitude, topography, orientation and climate conditions. The climatological data analyses of 30 years of Gilgit watershed has also been done to check the selected glaciers stability. A GPS field based land cover class comparison vs classification result for validation of the mapped glacier classes has been performed to check the accuracy assessment through an error matrix method. The kappa coefficient from the error matrix has been calculated to be 84.14%. A worthy support towards better appreciating of the watershed management and the hydrological responses in Gilgit watershed of the upper Indus catchment has been obtained through this study.