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Summary of Proposal LAN3180

TitleSpatial modeling of land subsidence vis--vis sea level rise in Karachi, Pakistan
Investigator KANWAL, Shamsa - The Hong Kong Polytechnic University, Department of Land Surveying and Geo-Informatics
Team Member
Professor DING, Xiao-li - The Hong Kong Polytechnic University, Department of Land Surveying and Geoinformatics
Dr. ZHANG, Lei - The Hong Kong Polytechnic University, Department of Land Surveying and Geoinformatics
Miss Kanwal, Shamsa - The Hong Kong Polytechnic University, Department of Land Surveying and Geo-Informatics
SummaryLand subsidence (LS) and Sea Level Rise (SLR) are inter-related as subsidence when it occurs in areas close to sea may cause relative sea-level rise in coastal environments. Consequently, LS may result in environmental hazards such as exhaustion of groundwater resources, damage of infrastructures, increase of risks of inundation and inland sea water intrusion. Pakistan, with about 1,600 km long coast, is no more exception to LS and SLR problems. The problems of ground subsidence induced by groundwater extraction combined with increasing SLR have caught much attention in recent years in the Karachi coast where urbanization has affected the underlying aquifer resources badly. However, causes of these changes are local rather global. Studies have been ringing the bell since last decade and issue of threat of land submergence have been raised on different points. National Institute of Oceanography (NIO) found that sea water intrusion and land subsidence pose a serious threat to Karachi. According to NIO, if one adds the projected rate of sea level rise of Arabian sea i.e. 8mm-10mm a year, even a few centimeters of subsidence could increase the risk of flooding from heavy rains or storm surges, salinization of fresh water aquifers, destruction of wetlands and conversion of low lying land into open sea. However, there has been no scientific study estimating the subsidence rate in coastal areas mainly due to lack of awareness on the serious threat posed by LS and seawater level rise as well as dearth of updated information related to human induced subsidence. This will be the first ever study of risk of land submergence due to SLR enhanced by ground subsidence. TerraSAR-X high resolution data will be used in conjunction with cohesive information on other causative factors like groundwater levels, sea level rise, soil etc. to fill the data and information gaps and map the subsidence and inundation risk in the study area. The objective of this project is to map subsidence in and around the city of Karachi, Pakistan, using TerraSAR-X high resolution images. Pakistan has been grouped by the UNEP's Oceans and Coastal Areas Programme Activity Centre among the countries which are most vulnerable to the effects of sea level rise. Increase in inundation risk due to subsidence caused relative sea level rise will be analyzed using cohesive information on the causative factors of subsidence and SLR. This study will use TerraSAR-X interferometry to measure and map subsidence around the city of Karachi using GAMMA software. We have already monitored this area with ENVISAT data. We aim for a comparison of these, about their resolution, wavelength and results for the monitoring of vertical displacements in low lying coastal areas. The project is funded by the Hong Kong Polytechnic University and Research Grant Council (RGC) of Hong Kong.

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