Rapid land sinking is making many coastal cities worldwide vulnerable to sea level rise, finds international group of scientists

20 Sep 2022 | Press Release

Author: Lauriane CHARDOT

Joint News Release

Land sinking linked to extraction of underground resources and rapid urbanisation 

A team of international scientists led by Nanyang Technological University, Singapore (NTU Singapore) has found that many densely populated coastal cities worldwide are vulnerable to sea level rise, because large amounts of their land are sinking. They suggest that an increase in industrial processes such as the extraction of groundwater, oil, and gas, as well as the rapid construction of buildings and other urban infrastructure may be contributing to this vulnerability. 

The team of researchers from NTU SingaporeUniversity of New Mexico, ETH Zürich, and NASA’s Jet Propulsion Lab managed by the California Institute of Technology, processed satellite images of 48 cities from 2014 to 2020 using a cloud-based processing system called Interferometric Synthetic Aperture Radar (InSAR).

Sea levels are rising globally as Earth’s ice sheets melt and as warming sea water expands. However, according to scientists, sinking land, or land subsidence, can aggravate the problem.

Land subsidence varies at a neighbourhood and even block level but across the 48 cities surveyed, the team found a median sinking speed of 16.2 millimeters (mm) per year, while some of them have land that is sinking at 43 mm a year. The current global mean sea-level rise is 3.7 mm/year.1

The results of the study were published in the scientific journal Nature Sustainability in September.

The findings are an example of research that supports the NTU 2025 strategic plan, which seeks to address humanity’s grand challenges on sustainability and accelerate the translation of research discoveries into innovations that mitigate human impact on the environment.

This research also contributes to the Singapore National Sea Level Programme (NSLP) supported by the National Research Foundation, Singapore and Singapore’s National Environment Agency. The programme aims to equip policy makers with the information they need to protect Singapore’s coasts.

Co-author Professor of Earth Sciences Emma Hill, Acting Chair of the Asian School of the Environment (ASE) at NTU, said: “In coastal areas, sinking land leads to higher sea level and an increased flood risk. Our findings enable affected communities and policymakers to identify which areas are at particular risk from high levels of land subsidence and take action to address their coastal risks.”

Co-author Assistant Professor Eric Lindsey, from the Department of Earth & Planetary Sciences at the University of New Mexico in the United States, said: “This study highlights the value of high-resolution satellite observations for better understanding this issue – subsidence rates can vary quickly across small areas, meaning that land-based measurements often do not capture the true scale of the problem”. He was a Research Fellow at NTU’s Earth Observatory of Singapore when he participated in the study.

First author of the paper, Ms Cheryl Tay, a PhD student at NTU’s ASE and the Earth Observatory of Singapore (EOS), who was sponsored under the NSLP Programme, said: “By estimating how much and how fast these densely populated coastal cities are subsiding, our study helps constrain projections of coastal flooding in the coming decades, as we expect more land to be flooded due to rising sea levels and land subsidence.”


Southeast Asia’s coastal cities sinking fastest

The 48 cities were selected based on the criteria of a minimum population of five million in 2020, and a maximum distance of 50 kilometres from the coast.

A comparison carried out by the researchers across coastal cities worldwide showed that the fastest velocities of relative local land subsidence are concentrated in Asia, especially in Southeast Asia (see Figure 1). 

The researchers chose to use InSAR as it provides accurate measurements of coastal sinking to a tenth of a millimetre. InSAR maps the deformation of ground using radar images of the Earth's surface that are collected from orbiting satellites. The InSAR datasets are larger and more accurate as unlike visible or infrared light, radar waves used by INSAR penetrate most weather clouds and are equally effective in darkness. 

Ms Tay added: “Rapid sinking of the land is frequently caused by groundwater extraction. This is concerning in Asia where many coastal cities are now centres of growth, and there is high demand for groundwater extraction to meet the water needs of growing populations.”

Prof Hill added: “Without serious mitigation efforts, a combination of rising seas, large populations living on low-lying coastal lands, and sinking lands will result in devastating consequences for many Asian cities.”  

“Our study highlights the fact that while this is a global issue, the response in many cases must be local. Slowing the rate of groundwater extraction to a sustainable level should be a top priority for all municipalities in coastal areas,” said Asst Prof Lindsey.

The researchers hope to further their study by projecting the rates of sinking land, factoring in variabilities and sensitivities from different climate and weather scenarios.

Figure 1: Populous cities experiencing the highest rates of local land subsidence are concentrated in Asia.
Figure 1: Populous cities experiencing the highest rates of local land subsidence are concentrated in Asia.

The research paper titled “Sea-level rise from land subsidence in major coastal cities” published in Nature Sustainability in Sep 2022. DOI https://doi.org/10.1038/s41893-022-00947-z

1 Intergovernmental Panel on Climate Change. Climate Change 2021: The Physical Science Basis (2021).

***END***

Media contact:

Mr Joseph Gan
Manager, Media Relations
Corporate Communications Office
Nanyang Technological University, Singapore
joseph.gan@ntu.edu.sg

Mr Steve Carr
Manager, Communications
University of New Mexico
scarr@unm.edu


About Nanyang Technological University, Singapore

A research-intensive public university, Nanyang Technological University, Singapore (NTU Singapore) has 33,000 undergraduate and postgraduate students in the Engineering, Business, Science, Medicine, Humanities, Arts, & Social Sciences, and Graduate colleges. 

NTU is also home to world-renowned autonomous institutes – the National Institute of Education, S Rajaratnam School of International Studies, Earth Observatory of Singapore, and Singapore Centre for Environmental Life Sciences Engineering – and various leading research centres such as the Nanyang Environment & Water Research Institute (NEWRI) and Energy Research Institute @ NTU (ERI@N).

Under the NTU Smart Campus vision, the University harnesses the power of digital technology and tech-enabled solutions to support better learning and living experiences, the discovery of new knowledge, and the sustainability of resources.

Ranked amongst the world’s top universities, the University’s main campus is also frequently listed among the world’s most beautiful. Known for its sustainability, over 95% of its building projects are certified Green Mark Platinum. Apart from its main campus, NTU also has a medical campus in Novena, Singapore’s healthcare district.

For more information, visit www.ntu.edu.sg


About the Earth Observatory of Singapore 

The Earth Observatory of Singapore (EOS) conducts fundamental research on earthquakes, volcanic eruptions, tsunamis, and climate change in and around Southeast Asia, toward safer and more sustainable societies. Established in 2009 as a Research Centre of Excellence at Nanyang Technological University, EOS has never been more important for Singapore and Southeast Asia. Disasters connected with natural hazards affect increasingly large populations, and in many cases are compounded by the threat of climate change and rising sea levels. EOS generates scientific breakthroughs that meet our societal needs and improve the lives of those that live in the region. 

For more information, visit www.earthobservatory.sg.


About The University of New Mexico 

Founded in 1889 as New Mexico’s flagship institution, The University of New Mexico occupies nearly 800 acres near old Route 66 in the heart of Albuquerque, a metropolitan area of more than 900,000 people. From the magnificent mesas to the west, past the banks of the historic Rio Grande to the Sandia Mountains to the east, Albuquerque is a blend of culture and cuisine, styles and stories, people, pursuits and panoramas. 

UNM is a place where cutting-edge research and creative endeavors flourish. UNM research injects millions of dollars into New Mexico’s economy, funds new advancements in healthcare, and augments teaching – giving students valuable hands-on training in state-of-the art laboratories. UNM is one of only a dozen Hispanic-Serving Institution in the U.S. that are also classified by the Carnegie Commission on Higher Education as a R1: Doctoral Universities with very high research activity.

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