Abstract
Barrier islands (BIs) have been designated as the first line of defense for coastal human assets against rising sea level. Global mean sea level may rise from 0.21 to 0.83 m by the end of 21st century as predicted by the Intergovernmental Panel on Climate Change (IPCC). Although the Indus Delta covers an area of 41,440 km² surrounded by a chain of BIs, this may result in an encroachment area of 3750 km2 in Indus Delta with each 1 m rise of sea level. This study has used a long-term (1976 to 2017) satellite data record to study the development, movement and dynamics of BIs located along the Indus Delta. For this purpose, imagery from Landsat Multispectral Scanner (MSS), Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), and Operational Land Imager (OLI) sensors was used. From all these sensors, the Near Infrared (NIR) band (0.7–0.9 µm) was used for the delineation and extraction of the boundaries of 18 BIs. It was found that the area and magnitude of these BIs is so dynamic, and their movement is so great that changes in their positions and land areas have continuously been changing. Among these BIs, 38% were found to be vulnerable to oceanic factors, 37% were found to be partially vulnerable, 17% remained partially sustainable, and only 8% of these BIs sustained against the ocean controlling factors. The dramatic gain and loss in area of BIs is due to variant sediment budget transportation through number of floods in the Indus Delta and sea-level rise. Coastal protection and management along the Indus Delta should be adopted to defend against the erosive action of the ocean.
Highlights
Global warming, being caused by the increase in temperature and atmospheric CO2, acts as a catalyst in the melting of glaciers, expansion of ocean water, increase in sea surface temperature, rise in sea-level, and increase in tropical storms intensity [1,2,3,4,5,6]
For barrier islands (BIs) 1 to the 1976 boundary was used as a reference to gauge the movement of the BIs, while it should be noted that for BIs to 18 there is no boundary for the year 1976 which was due to the unavailability of the L2 Multispectral Scanner (MSS) image satisfying the image selection criteria (Figure 2), 1990 boundary was used as a reference
An archive of Landsat imagery from 1976 to 2017, has been used in this study to explore the morphological changes in the barrier island of the Indus Delta Region (IDR)
Summary
Global warming, being caused by the increase in temperature and atmospheric CO2, acts as a catalyst in the melting of glaciers, expansion of ocean water, increase in sea surface temperature, rise in sea-level, and increase in tropical storms intensity [1,2,3,4,5,6]. Coastal topography may constantly change with numerous oceanic and physical processes including tidal flooding, SLR, and tsunami effect. This may cause sinking of low-land areas, and erosion of sediments which is a great concern for coastal researchers and investigators [10,11,12,13,14]. IDR is experiencing geomorphological changes in all areas along its major and minor creeks in the form of erosion processes and low deposition rate of sediment budget from Indus River during post-damming era [35]. IDR has been considered as one of the most dynamic deltaic systems which consists of 16 major tidal inlets having 17,000 km area with an active tidal flat area of 10,000 km, significant number of BIs [36] and hosts world’s largest arid mangrove forest [37]
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