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PolyU research reveals sharp depletion in soil moisture, driving land water to flow into the oceans and contributing to a rise in sea levels

The increasing frequency of once-in-a-decade agricultural and ecological drought has underscored the urgency of studying hydrological changes. A research team from the Department of Land Surveying and Geo-informatics of The Hong Kong Polytechnic University (PolyU) has collaborated with international experts to analyse the estimated changes in land water storage over the past 40 years by utilising space geodetic observation technology and global hydrological change data. This innovative method has revealeda rapid depletion in global soil moisture, resulting in a significant amount of water flowing into the oceans, leading to a rise in sea levels. The researchprovides new insights into the driving factors behind the alarming reduction in terrestrial water storage and rise in sea levels. The findings have been published in the international journal Science. Since polar motion reflects mass redistribution within the Earth system, integrating models and observations across the atmosphere, hydrosphere and lithosphere is crucial. However, previous challenges in measuring terrestrial water storage, particularly groundwater and root zone soil moisture, limited understanding of hydrological depletion at continental scales. Prof. Jianli CHEN, Professor of the PolyU Department of Land Surveying and Geo-informatics and core member of the Research Institute for Land and Space and the international team employed satellite altimetry and gravity missions, including the Gravity Recovery and Satellite Experiment (GRACE), and GRACE Follow-On, to enable continental-scale observations of terrestrial water storage variations. By integrating this with global mean sea levels and polar motion data, the team has explored terrestrial water storage depletion patterns. Notably, this study introduced novel methods for estimating global soil moisture, which improves the accuracy of continental and global scale modeling to enable a more effective understanding of soil moisture variations under climate change. The melting of Greenland’s ice sheet is recognised as the largest single contributor to the rise in global sea levels, adding approximately 0.8mm annually. This study reveals that between 2000 and 2002, the global terrestrial water storage significantly declined, with a total of 1,614 billion tons of water lost to the oceans, which is twice as much as resulting from the current melting of Greenland ice, and equivalent to a 4.5mm rise in sea levels. Since then, the rapid loss of terrestrial water storage has been followed by a more gradual but continuous depletion, with no signs of recovery. In addition, compared to the period from 1979 to 1999, a notable decline in global average soil moisture was observed from 2003 to 2021. Between 2003 and 2011, the Earth’s pole shifted 58cm toward 93° East Longitude, demonstrating that the continued decline in soil moisture is leading to a reduction in terrestrial water storage. The team also pointed out that precipitation deficits and stable evapotranspiration caused by global warming, changing rainfall patterns and increasing ocean temperaturesare likely the key factors for the abrupt decline in terrestrial water storage. The ERA5-Land soil moisture data of the European Centre for Medium-Range Weather Forecasts’ corroborates these findings, showing substantial terrestrial water storage losses in Africa, Asia, Europe, and South America. In Asia and Europe, the affected areas expanded from northeastern Asia and eastern Europe to broader regions across East and Central Asia, as well as Central Europe, following the sharp water storage depletion observed between 2000 and 2002. With increasing agricultural irrigation in regionssuch as northeast China and the western United States, and global greening, soil moisture may further diminish in semi-arid areas with intensive agriculture and high levels of greening. The team suggests the need for improved land surface models which consider these factors for a more comprehensive understanding of long- term changes in terrestrial water storage. Prof. Jianli Chensaid, “Sea level change and Earth rotation serve as indicatorsof large-scale mass changes in the Earth system. Accurately measured sea level change and variation in Earth rotation provide a unique tool for monitoring large-scale mass changes in the global water cycle. By integrating multiple modern space geodetic observations, it enables comprehensive analysis of the driving factors behind changes in terrestrial water storage and sea level rise. This, in turn, provides reliable data for climate and Earth system science experts to further investigate drought issues, aiding authorities in formulating water resource management and climate change mitigation strategies to address new challenges posed by climate change.” More information can be found in the Media Release (PolyU research reveals sharp depletion in soil moisture, driving land water to flow into the oceans and contributing to a rise in sea levels) of PolyU.

The Third ACOWS Workshop Successfully Held at PolyU

The third Workshop on Atmospheric and Coastal Observations for Weather Servicing (ACOWS 2025) was hosted by Prof. George Liu at the Department of Land Surveying & Geo-Informatics (LSGI), the Hong Kong Polytechnic University (PolyU) during 2-3 April 2025. This year’s theme, “Data Assimilation for a Better Weather Forecasting”, brought together experts to explore cutting-edge advancements in weather prediction methodologies. Renowned scientists from Mainland China were invited to attend this workshop and present their work. They are Prof. Jianhua Sun from the Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing; Prof. Yaodeng Chen from the School of Atmospheric Sciences, Nanjing University of Information Science and Technology; Dr. Yerong Feng, Director, from the Guangdong–Hong Kong–Macao Greater Bay Area Weather Research Center for Monitoring Warning and Forecasting, Shenzhen; Dr. Yuanfu Xie, Chief Scientist, from the Guangdong–Hong Kong–Macao Greater Bay Area Weather Research Center for Monitoring Warning and Forecasting, Shenzhen; Prof. Donghai Wang from the School of Atmospheric Sciences, Sun Yat-sen University; and Dr. Chunqing Shang, the Huawei Technologies Co. Presentations centered on innovative approaches to “Forecasting of Heavy Rainfall using multi-source PWV data assimilation and ensemble prediction”, a work package being led by Prof George Liu and funded by the Otto Poon Research Institute For Climate-Resilient Infrastructure (RICRI) at the PolyU. Discussions highlighted the integration of multi-source data to enhance predictive accuracy and address climate resilience challenges.   The workshop fostered interdisciplinary collaboration, bridging academic research with operational weather servicing needs.

LSGI Participates in Geo Connect Asia 2025: Showcasing Geospatial Solutions and Building Partnerships in South-East Asia

The Department of Land Surveying and Geo-Informatics (LSGI) participated Geo Connect Asia 2025, held from 9 to 10 April in Singapore. Led by Prof. Wu Chen (Head of the Department), alongside with Prof. Wallace LAI (Associate Head of Teaching) and supported by academic staff including Prof. Xintao Liu and Prof. Tony Zhuge, showcased its geospatial solutions and academic programs, fostering international collaboration and innovation.   Promoting Academic Excellence and Geospatial Innovation LSGI set up an engaging booth at the event, highlighting its comprehensive Bachelor and Master Degree programs. Moreover, the booth served as a platform to demonstrate innovative geospatial solutions developed by six of LSGI's distinguished professors. Attendees were captivated by the department's commitment to advancing geospatial intelligence and its practical applications in various sectors.   Insightful Discussions on Geospatial Intelligence and Infrastructure Development On the first day of the conference, Prof. CHEN Wu participated in a dynamic panel discussion alongside industry leaders, exploring the transformative role of geospatial intelligence, AI, and open data in shaping the future. Prof. Chen emphasized Hong Kong’s spatial data infrastructure, showcasing how tools like Large Language Models (LLMs) are revolutionizing road planning and environmental impact assessments. Simultaneously, Prof. Wallace Lai delivered presentation at the Digital Underground Connect segment, titled “The Power of The Digital Underground Twin - Enabling Smart, Safe, and Sustainable Asset Management and Infrastructure Development.” Prof. Lai shared insights from Hong Kong's subsurface utility mapping programs, offering solutions and technologies that are setting new standards in infrastructure development.   Building Strategic Partnerships for Future Growth Throughout the two-day event, LSGI engaged with people from industry in Singapore, including Managing Director from HSC Pipeline Engineering Pte Ltd and representative from the Singapore Institute of Surveyors and Valuers (SISV). These discussions paved the way for future collaborations, with HSC offering internship and employment opportunities for LSGI students and graduates, and SISV expressed interest in further cooperation with LSGI.   Strengthening Ties with the Singapore Land Authority In addition to the conference activities, the LSGI delegation visited the Singapore Land Authority (SLA), where they have discussed for future enhanced collaboration. This agreement focuses on capacity building and accreditation in academic programs, marking a significant step towards strengthening educational and professional ties between Hong Kong and Singapore.

LSGI Leadership Strengthens International Ties with Visit to Malaysia

From 6 to 8 April 2025, Prof. Wu Chen, Head of the Department of Land Surveying and Geo-Informatics (LSGI), led a delegation to Malaysia alongside Prof. Wallace Lai, Associate Head of Teaching from LSGI. The trip aimed to enhance academic collaborations and gain insights into the geo-spatial and land surveying industry in Malaysia.   Exploring Malaysia's Geo-Spatial Industry The delegation's first major visit was to the Department of Survey and Mapping Malaysia (JUPEM). Prof. Chen and Prof. LAI were provided with an in-depth overview of Malaysia's geo-spatial and land surveying industry. On the other hand, JUPEM also shared their works on Building Information Modelling (BIM) and Utility Surveying in Malaysia. This visit offered valuable perspectives on the country's advancements in mapping technologies and spatial data management, paving the way for potential collaborative projects and knowledge exchange.   Accreditation and Professional Recognition The second key visit was to the Lembaga Jurukur Tanah (LJT), the esteemed house of surveyors in Malaysia. Discussions centred around the accreditation and professional recognition of the LSGI Bachelor Programme. This engagement underscored LSGI's commitment to maintaining high educational standards and achieving international recognition for graduates, ensuring they are well-prepared for any global opportunities.   Fostering Academic Collaboration with UTM The final visit was to the University of Technology Malaysia (UTM), where Prof. Chen and Prof. Lai explored opportunities for future collaboration in academic programmes and research initiatives. The discussions with UTM representatives highlighted mutual interests in advancing educational offerings, introducing their practical programmes for training experts for Malaysia’s industry and reinforcing LSGI's dedication to expanding its global academic network.   This visit reflects LSGI's ongoing efforts to explore international partnerships in south-east Asia.

LSGI Hosts RICS Accreditation Visit

On 27 March 2025, the Department of Land Surveying and Geo-Informatics (LSGI) welcomed a visit from the Royal Institution of Chartered Surveyors (RICS) for an Accreditation and Reaccreditation review. This visit reflects LSGI’s ongoing efforts to maintain quality education and industry relevance. During the one-day visit, the RICS team toured LSGI’s facilities, including various laboratories and survey equipment store, to understand the resources available for research and teaching. The team also attended a presentation on the unique aspects of LSGI’s programmes, highlighting the department's focus on providing up-to-date education in land surveying and geo-informatics. The visit featured engaging meetings with LSGI staff, students, and industry representatives, offering insights into the collaboration between academia and industry to ensure programmes meet professional standards. The RICS visit underscores LSGI's dedication to high educational standards and strong industry ties. LSGI looks forward to continuing its partnership with RICS to enhance its programmes. For more information about LSGI’s programmes and initiatives, please visit https://www.polyu.edu.hk/lsgi/study/.

Staff Highlights: Prof. Guoqiang SHI

Urbanization brings rapid development but also exacerbates geological and environmental risk, such as land subsidence, infrastructure instability, and landslides. These challenges threaten the safety of millions and demand advanced monitoring solutions. Prof. Guoqiang Shi and his team work on urban remote sensing, leveraging Interferometric Synthetic Aperture Radar (InSAR) to monitor and analyse urban geological vulnerabilities from underground, ground surface, to the built upper ground. By integrating InSAR remote sensing, big data analytics and artificial intelligence (AI), the team aims to provide critical insights for urban resilience, infrastructure maintenance, and sustainable development.   Topic 1: Uneven Settlement in Coastal Reclamations Reclaimed areas, common in land-scarce cities like Hong Kong, are prone to uneven settlement due to soft subsurface layers. Constrained by its steep terrain, Hong Kong has over 25% of its developable land reclaimed from the sea. Using spaceborne InSAR, we detected rapid subsidence at Hong Kong International Airport’s Third Runway, a major reclaimed project. Our high-resolution data revealed soil compression patterns and fill-layer dynamics, offering engineers and policymakers actionable insights for soil reinforcement, infrastructure planning, and future reclamation projects (e.g., the ‘Lantau Tomorrow Vision’). This work underscores the need for continuous monitoring in reclaimed zones to prevent long-term risks.   Topic 2: Groundwater and Urban Land Subsidence Unlike the artificial foundations in Hong Kong, the Yangtze River Delta (YRD) has vast and flat areas of natural sediments. Excessive groundwater extraction has caused severe subsidence in cities like Suzhou, where some areas sank over 2 meters before extraction was banned in 1997. Using InSAR, we quantified the slowdown in subsidence post-ban, demonstrating the policy’s effectiveness. However, traditional geological and surveying methods failed to evaluate the groundwater policy on a city-wide scale. Figure 2 illustrates the post-ban recovery (slowing) of Suzhou’s land subsidence, as captured by satellite InSAR. These findings are vital for groundwater management in vulnerable regions (e.g., the North China Plain), supporting sustainable urban planning and resource policies.   Topic 3: Infrastructure Health and Slope Safety Beyond subsurface risks, InSAR enables large-scale structural and slope safety monitoring. In Hong Kong, we applied it to assess highway stability and generate 3D building point clouds, identifying high-risk structures. Risky slopes/landslides adjacent to buildings/transportations can be surveillance timely and located for accurate mitigation and evacuation planning. As satellite data improves, InSAR is becoming indispensable for smart city platforms, offering precise, real-time diagnostics for next-generation urban resilience solutions.   Photo 2: Reclamation subsidence and soil consolidation of the HKIA 3rd RunwayPhoto 3 & 4: Urban land subsidence recovery in Suzhou City following the implementation of groundwater extractionPhoto 5: InSAR 4D data for infrastructure and slope safety assessment   Welcome to join Prof. Shi’s team! Prof. Shi and his team are advancing InSAR algorithms for complex urban terrains and developing AI-driven models to mine geohazard data. They welcome students from diverse academic backgrounds to join LSGI and join our group. For contact details, please refer to the information below. They are looking forward to collaborating with you!   Personal web: https://guoqiangshi.github.io/ LSGI web: https://www.polyu.edu.hk/lsgi/people/academic-staff/ Email: guoqiang.shi@polyu.edu.hk   References: Jiang Z, Shi G, Wu S, et al. Unveiling multimodal consolidation process of the newly reclaimed HKIA 3rd runway from satellite SAR interferometry, ICA analytics and Terzaghi consolidation theory. Remote Sensing of Environment, 2025, 318: 114561. https://doi.org/10.1016/j.rse.2024.114561 Shi G, Huang B, Leung A K, et al. Millimeter slope ratcheting from multitemporal SAR interferometry with a correction of coastal tropospheric delay: a case study in Hong Kong. Remote Sensing of Environment, 2022, 280: 113148. https://doi.org/10.1016/j.rse.2022.113148 Shi G, Ma P, Hu X, et al. Surface response and subsurface features during the restriction of groundwater exploitation in Suzhou (China) inferred from decadal SAR interferometry. Remote Sensing of Environment, 2021, 256: 112327. https://doi.org/10.1016/j.rse.2021.112327 Shi G, Lin H, Bürgmann R, et al. Early soil consolidation from magnetic extensometers and full resolution SAR interferometry over highly decorrelated reclaimed lands. Remote Sensing of Environment, 2019, 231: 111231. https://doi.org/10.1016/j.rse.2019.111231 Shi G, Lin H, Ma P. A hybrid method for stability monitoring in low-coherence urban regions using persistent and distributed scatterers. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2018, 11(10): 3811-3821. https://doi.org/10.1109/JSTARS.2018.2867832      

Prof. Yang Xu Honored with Outstanding Alumni Award from University of Tennessee, Knoxville

Prof. Yang Xu, Associate Head of Partnership and Associate Professor, has been awarded the prestigious Outstanding Alumni Award by the Department of Geography and Sustainability at the University of Tennessee, Knoxville. This accolade celebrates Prof. Xu's remarkable mid-career achievements and his significant contributions to the field of Geographic Information Science. University of Tennessee, Knoxville (UTK) is a public land-grant research university in the United States. The university is also classified among "R1: Doctoral Universities – Very high research activity" according to the Carnegie Classification of Institutions of Higher Education. This classification highlights the university's emphasis on research excellence and its role in promoting the academic and professional growth of its alumni. Congratulations to Prof. Xu!

LSGI Alumni Appointed as Tenure-Track Assistant Professor at Nanjing University

Dr. Jiaqi Tian, a former Ph.D. graduate from the Department of Land Surveying and Geo-Informatics (LSGI) at the Hong Kong Polytechnic University (PolyU), has been appointed as a tenure-track assistant professor at the International Institute of Earth System Science (ESSI) at Nanjing University. Under the mentorship of Professor Xiaolin Zhu and through his work at the PRIDE (PolyU Remote Sensing Intelligence for Dynamic Earth) Lab, Dr. Tian earned his Ph.D. in 2021 and developed his expertise and research capabilities in his field. ESSI is a leading academic institution in the fields of quantitative remote sensing and terrestrial carbon cycle research. LSGI is honoured by his career milestone.   Congratulations to Dr. Tian on this well-deserved achievement!   Dr Jiaqi Tian’s Personal Web Page: https://scholar.google.com/citations?user=RNCJZEYAAAAJ&hl=en PRIDE Lab: https://xzhu-lab.github.io/

PolyU Achieves Prestigious Global Rankings in Geography and Remote Sensing

The Hong Kong Polytechnic University (PolyU) has achieved impressive global rankings, highlighting its academic excellence. PolyU's Geography programme is ranked 37th in the QS World University Rankings by Subject 2025, and its overall QS ranking has risen to 57th in 2025. The Remote Sensing discipline has also advanced significantly, moving from 38th in 2023 to 15th in the ShanghaiRanking's Global Ranking of Academic Subjects 2024. These accomplishments reflect the Department of Land Surveying and Geo-Informatics (LSGI)’s commitment to excellence in academics, research, and industry partnerships, showcasing our dedication to advancing knowledge in Geography and Remote Sensing. PolyU's achievements affirm its status as a leading institution in the Asia-Pacific region and beyond. By fostering innovation and collaboration, the university attracts top talent and forms strategic partnerships, enhancing its academic and research strengths. LSGI is proud of its contributions to these successes. For more details, you can visit the QS University Subject Rankings for Geography and the ShanghaiRanking's Global Ranking of Academic Subjects 2024 for Remote Sensing.

Successful Conclusion of LSGI Career Talk 2025: Bridging Opportunities in Private and Government Sectors

The LSGI Career Talk Series 2025 concluded successfully, offering invaluable insights into career paths and recruitment strategies across both private and government sectors. Held on February 21st and 28th, and March 7th, the series featured a diverse line-up of speakers from six prominent private companies alongside with government sectors. Session I – Private Company The event kicked off with the private sector session on 21 February, where industry leaders from six dynamic companies, including ARUP, Build King, China State Construction Engineering, Esri China (Hong Kong), Leica Geosystems and Ming Hing Waterworks. Industry leaders shared their expertise and provided attendees with a comprehensive understanding of the current job market trends. Participants gained first-hand knowledge about the skills and attributes sought by employers, as well as practical tips on how to navigate the recruitment process effectively. Session II – The Government of the HKSAR Following the private sector insights, the government sector sessions on 28 February and 7 March offered attendees a unique perspective on careers within public service. Speakers from the Lands Department, Planning Department, Highway Department and Civil Engineering and Development Department highlighted the rewarding opportunities available in government roles, emphasizing the importance of public service and the impact these positions have on community development and planning. Throughout the series, attendees had the opportunity to engage directly with speakers during interactive Q&A sessions, fostering a dynamic exchange of ideas and advice. The event served as a valuable platform for networking, allowing participants to connect with industry professionals and explore potential career paths. Thank you to all speakers for their fruitful sharing to near 300 students of LSGI in these sessions.