Morphological change detection along the shoreline of Karachi, Pakistan using 50 year time series satellite remote sensing data and GIS techniques

Changes taking place along the shoreline are attributed to several physical and dynamical processes. Sindh Coast of Pakistan particularly Karachi is continuously under the process of morphological changes due to anthropogenic activities and natural processes. This study examined spatiotemporal morphological changes over five decades (1972–2020) along Karachi Coast bordering Arabian Sea using SRS and GIS techniques. This study reveals major morphological changes along the shoreline of Karachi in the vicinity of Karachi Port, Clifton Beach, Bundal Island and Port Qasim, which have been calculated in the form of erosion and accretion using erase tool of ArcGIS software. Quantitative analysis shows highest accretion of >15.50 km2, at the Eastern End of Clifton Beach due to human intervention. Natural processes caused major erosion (10.95 km2) and accretion (19.50 km2) during 1972–2020 in the vicinity of Bundal Island. During 2011–2020, significant change (2.40 km2) is observed opposite to Port Qasim causing damage to mangrove vegetation of 1.40 km2 calculated using NDVI. Highest rate of erosion (0.31 km2year−1) and highest rate of accretion (0.70 km2year−1) are found in Bundal Island during 1972–1987 and 1987–1999, respectively. Maximum increase in the length of shoreline (6.78 km) is depicted at Eastern End of Clifton Beech between 1999–2010.岸线的动态演化由多种物理动力过程共同作用所致。巴基斯坦信德省沿岸，尤以卡拉奇海岸为甚，因人类活动与自然过程的双重影响，正持续发生地貌形态演化。本研究借助合成孔径雷达（Synthetic Aperture Radar，SRS）与地理信息系统（Geographic Information System，GIS）技术，对毗邻阿拉伯海的卡拉奇海岸1972—2020年这五十年间的时空地貌变化展开分析。研究识别出卡拉奇港、克利夫顿海滩、班达尔岛与卡西姆港周边岸线的主要地貌变化，并通过ArcGIS软件的擦除工具量化了岸线的侵蚀与淤积规模。定量分析结果表明，受人类活动干预，克利夫顿海滩东端的淤积面积最大，超过15.50平方千米。1972—2020年间，班达尔岛周边区域受自然过程主导，分别出现10.95平方千米的侵蚀与19.50平方千米的淤积。2011—2020年，卡西姆港对岸区域出现显著岸线变化（面积达2.40平方千米），导致1.40平方千米的红树林植被受损，该结果通过归一化植被指数（Normalized Difference Vegetation Index，NDVI）计算得出。1972—1987年与1987—1999年期间，班达尔岛分别出现了最高的侵蚀速率（0.31平方千米/年）与淤积速率（0.70平方千米/年）。1999—2010年，克利夫顿海滩东端的岸线长度增幅最大，达6.78千米。