| Author: | Kanwal, Shamsa |
| Title: | Study of ground displacements, erosion and sea level rise along Karachi coast, Pakistan |
| Advisors: | Ding, Xiaoli (LSGI) Zhang, Lei (LSGI) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Coast changes -- Pakistan -- Karachi Environmental risk assessment -- Pakistan -- Karachi Environmental degradation -- Pakistan -- Karachi Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Land Surveying and Geo-Informatics |
| Pages: | 180 pages : color illustrations |
| Language: | English |
| Abstract: | With communities increasingly concentrated in coastal regions globally, nations call for comprehensive risk assessments for risk-informed planning, smart decision-making, and resource treatment to aid future sustainability in view of global climate change. In the wake of threatening coupled processes, i.e., erosion, increasing sea level rise (SLR), ground displacement and anthropogenic pressures on coastal systems, it is essential to track the coastline changes, particularly those bordering the developing and low-lying deltaic coasts, to take appropriate measures for their stability. To provide the evidence from Pakistan, this study focuses on Pakistan’s largest and coastal megacity of Karachi inhibiting 23 million lives, and the population density has been increasing rapidly in recent decades, with as yet, no signs of stabilizing. A scenario of recent development projects in and around the city of Karachi, set in the context of predicted sea level increase and more significant coastline erosion variability due to climate change, is cause for concern. Any increase in coastal degradation in Karachi and the neighboring Indus River delta could cause widespread economic and social distress. This study evaluates the available sources of coastline erosion, sea level, and ground displacement data to study the interplay and disastrous impacts of these coupled processes in the study area. This study, for the first time, provide a spatio-temporal framework to assess the morphological change and the state of erosion along the entire 320 km long Sindh coastline of Pakistan over the past three decades using the well-known Digital Shoreline Analysis System (DSAS) developed by the USGS. Landsat images from 1989 to 2018 are used to examine the state of coastline erosion using different statistical approaches such as End Point Rate (EPR), Linear Regression Rate (LRR) and Least Median of Squares (LMS). It is found that coastal erosion is very substantial and widespread along the entire coastline. However, the rate of erosion varies across the study area, with a general trend of increasing erosion from the west in Karachi to the east in the IDR. The eastward inclreasing spatial trend is positively correlated with mean relative sea level rise, which has increased from ~1.1 mm/year to ~1.9 mm / year and negatively correlated with the topographic slope, which is found to be decreasing eastward along the coastline. The majority of the barrier islands (15 out of 19) located along the study area coastline, is found to be eroding, which is positively correlated with reduced sand supply and increasing mean relative SLR rate. Furthermore, results from coastal erosion are analyzed in relation to the relative sea level trend estimated from satellite altimetry gridded product from ESA’s Climate Change Initiative (CCI) project. The last part of the study employed interferometric data analysis techniques with synthetic aperture radar (SAR) data to assess the vertical ground displacements which may be related to climatic trends of sea level variation and coastline retreat. Results obtained from this investigation suggest that some areas along the Karachi coast are subsiding at rates comparable, even much higher than the relative SLR, which may amplify the rates of the relative SLR in years to come and accelerate coastal erosion. While erosion affects most of the eastern parts of the study area, the subsidence is spatially variable across the study area along the coastline. Erosion rates of ~2.4 m/yr spatially corresponded with subsidence rates of up to ~ -1.4 cm/yr, , but not all coastline segments with high annual mean erosion rates were associated with local mean subsidence. While the results from this study are essential for effective coastal planning and implementing appropriate measures to reduce the coastal erosion and associated risks in Pakistan, the study acts as a road map to scale-down the regions with higher vulnerability to the coupled processes for further in-depth assessments. The spatial assessments made in this study provides a spatial reference and information for the prioritization of different segments of coastline for appropriate measures. In view of the depleting resource of BIs which provides a natural defense to the coast where sea levels are rising, the overall finding of the study is that the compound effect of climate change-induced rise in sea levels, coastal subsidence and erosion in the low-lying coastal regions of the study area will be manifold. The pressing need for integrated adaptation measures for monitoring, creating databases, and periodic assessment is an important prerequisite for proactive planning, follow up and sustainable development in order to reduce the risks and hazards posed to the coastal regions. |
| Rights: | All rights reserved |
| Access: | open access |
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