Asian cities are sinking faster than the rate of sea level rise just not because of climate change but for a new phenomenon – land subsidence, according to a new study.
The cities where land subsidence has been the fastest (over 20 mm/yr LOS) from 2015 to 2020 are in South, Southeast, and East Asia, noted the study published in Geophysical Research Letters
The highest subsidence rates appear in Tianjin, Semarang, and Jakarta, where maximum rates exceed 30 mm/yr LOS-dwarfing global mean sea level rise by almost 15x. If subsidence continues at recent rates, these cities will be challenged by severe flood events much sooner than projected by sed level rise models, the study added.
SOME FAST SINKING CITIES
- Chittagong (Bangladesh), Tianjin (China), Manila (Philippines), and Karachi (Pakistan). The maximum subsidence rate in Tianjin exceeds 40 mm/yr LOS (almost 20x mean sea level rise), in Chittagong and Manila exceeds 20 mm/yr LOS (almost 10x mean sea level rise), and in Karachi exceeds 10 mm/yı (approximately: 5x mean sea level rise) Istanbul, the capital of Turkey with a population of 15 million. An area of 5 * 20 km on the west end of the city is sinking faster than 2 mm/yr LOS.
- Taipei is the capital of Taiwan. It is the largest city in Taiwan, with a population of 2.7 million. It is in a basin on the north end of the island. Most of the city shows subsidence of more than 2 mm/yr LOS
- Mumbai is the second-most populous city in India after Delhi.A significant portion of the city is subsiding more rapidly than 2 mm/yr LOS
- The Tampa Bay Area surrounds Tampa Bay on the west coast of Florida (United States). A large area on the northwest side of the Tampa Bay area, including a 25-kin-long section along the coast, is subsiding faster than 2 mm/yr. The estimated area of this low-elevation, fast-subsiding portion of the Tampa metropolitan area is close to 800 km.
METHOD
The study covered 99 coastal cities all over the world, 33 of which have areas or parts that have subsided by more than a centimetre per year. Researchers Pei-Chin Wu, Matt Wei and Steven D’Hondt from the Graduate School of Oceanography at the University of Rhode Island used satellite based Interferometric Synthetic Aperture Radar to identify “fast-subsiding areas”.
CAUSES
- Castal vertical motions including Glacial Isostatic Adjustment (GIA) and non-GIA components
- Glacial Isostatic Adjustment occurs mostly in high-latitude regions with a slow and steady rate (a few mm/yt)
- Tectonic movement affects areas with active faults in both steady and transient manner.
- Although sediment and aquifer compaction can happen naturally, they can be greatly accelerated by human activities, including ground water extraction related to rapid urbanization and population growth, oil and gas production and new building loads.
- The dominant processes and their contributions to coastal subsidence vary from place to place, making it a challenging task to understand and address coastal subsidence
