Land subsidence: A global challenge.

This study presents a comprehensive review of the Land subsidence (LS) cases, as a worldwide environmental, geological, and global geohazard concern. Here, 290 case studies around the world mostly conducted in large metropolitan cities (e.g. Bangkok, Beijing, California, Houston, Mexico City, Shanghai, Jakarta, and Tokyo) in 41 countries were collected. The spatial distribution of LS characteristics (e.g. intensity, magnitude, and affected area), impacts, and influential factors are scrutinized. Worldwide attempts to remedy the crisis of LS were also investigated in this review. It is shown that the coastal plains and river deltaic regions are of high-frequent subsided areas around the world (~47% of 290 study areas). The spaceborne monitoring of LS is the more prevalent technique (~ 38% of total cases) compared to the ground-investigation (e.g. geological surveying, leveling, GPS, and modeling). Human-induced LS cases are 76.92% of all the LS cases around the world and groundwater extraction contributes 59.75% of these cases. Strong direct correlations with the exponential trend are observed between the average LS rate (LS _avg ) with groundwater withdrawal (R ²  = 0.950) and groundwater level decline (R ²  = 0.888). To understand the influential factors on LS occurrences, the relationship of LS rate with climate factors, hydrogeological characteristics of the aquifer, human-induced factors are investigated. Finally, we provide future research guidelines and implications that need to be expanded in order to better monitor and reduce the impact of the LS phenomenon. The outcomes of this study can be used to derive a framework helpful for interpreting the observed LS phenomena and for forecasting future situations to mitigate or control this geohazard.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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