Chaofan Zhou

Spatial correlation between land subsidence and urbanization in Beijing, China

The large-scale construction of buildings, extensive road and rail networks, and increased traffic flow associated with urbanization has the potential to cause land subsidence. Land subsidence caused by urbanization is an increasingly significant problem in Beijing, China; therefore, it is important to investigate the relationship between urbanization and land subsidence. Landsat TM images covering the Beijing plain were used to acquire spatial changes information of built-up areas by calculating an index-based built-up index (IBI). We used ENVISAT Advanced Synthetic Aperture Radar data acquired from 2003 to 2009 and persistent scatterers for SAR interferometry (PSI) technology to estimate land subsidence. Geographic information systems spatial analysis method was used to identify the relationship between the settlement rate and the IBI value for three different sampling units. The result showed that it was a positive correlation between construction density and land subsidence; for land subsidence, the effect from the combination of high-density building clusters and extensive transportation networks was more significant than the presence of buildings alone. However, there may be a delay between the completion of building construction and the development of land subsidence.

Characterization and causes of land subsidence in Beijing, China

ABSTRACT Long-term overexploitation of groundwater is the primary factor causing regional land subsidence in the Beijing plain area, China. Currently, large subsidence funnels exist, one each in southern and northern Beijing. We adopted the multi-temporal interferometric synthetic aperture radar (MT-InSAR) method, incorporating both persistent scatterer (PS) and small baseline (SB) approaches on 47 Envisat Advanced Synthetic Aperture Radar (ASAR) single look complex (SLC) images to map land subsidence in the Beijing plain area. The temporal and spatial variations of land subsidence and its seasonal variation were explained by the MT-InSAR results. Then, the InSAR results were combined with the dynamic monitoring of groundwater level, extensometer measurements, and hydrogeological data; the characterization and causes of land subsidence were analysed with Geographic Information System (GIS) spatial analysis methods. The results show the following. 1) Land subsidence developed rapidly in the Beijing plain area from 2003 to 2010, with obviously uneven settlement; settlement rates exceeded 100 mm year−1 in some areas. Seasonal variation in settlement rates may be affected by changes in the precipitation rates and the exploitation of groundwater. 2) The contribution of different aquifer systems to land subsidence varies. The variation in the groundwater level in the second confined aquifer, at a depth of 100–180 m, has the greatest impact on land subsidence. 3) The settlement is centred in the lower part of the Wenyu–Chaobai and Yongding alluvial fan areas, where the compressible layer is more than 100 m thick. Meanwhile, land subsidence forms a structural feature with larger differences in the deformation gradient on both sides of faults.

Land subsidence under different land use in the eastern Beijing plain, China 2005-2013 revealed by InSAR timeseries analysis

Land subsidence has been occurring in Beijing since the 1970s. Five major land subsidence areas have been formed: Dongbalizhuang–Dajiaoting, Laiguangying, Changping Shahe–Ba Xianzhuang, Daxing Yufa–Lixian, and Shunyi–Ping Gezhuang. In this paper, we studied on land subsidence in Dongbalizhuang–Dajiaoting and Laiguangying using small baseline subset interferometry and interferometric point target methods of 47 ENVISAT ASAR and 29 RADARSAT-2 data. The results showed that the degree of land subsidence in these areas varied significantly. The mean land subsidence rate ranged from 143.43 to 8.2 mm/a and from 132.11 to 7.3 mm/a during 2005–2010 and 2011–2013, respectively. We correlated the observed settlement with the land use (agricultural, residential, and industrial). Displacement in the agricultural areas was greater than that in the other areas from 2005 to 2013. Moreover, we compared the observed deformation and the groundwater level in phreatic and confined aquifers. There was a strong correlation between ground subsidence and the groundwater level and the ground settlement increased with a decrease in the groundwater level and the maximum correlation coefficient can reach 0.525. Furthermore, subsidence appeared to be associated with compressible deposits, suggesting that for 90–210-m thick compressible deposits, ground settlement is more likely to occur as the thickness of the compressible layer increases.

Spatial–temporal evolution patterns of land subsidence with different situation of space utilization

Long-term over-exploitation of underground water, static and dynamic load is increasing year by year, which influenced the occurrence and development of regional land subsidence in Beijing, China. We used Envisat advanced synthetic aperture radar data acquired from 2003 to 2009 and PSI (persistent scatterers for SAR interferometry) and small baseline technology to estimate regional land subsidence information in Beijing, China. In different situation of space utilization, we chose five typical settlement areas according to classified information of land-use, multi-spectral remote sensing images and geological data. We analyzed the time-series evolution characteristics of uneven subsidence by GIS spatial analysis. The comparative analysis results suggest that for five typical settlement areas, the complex situations of space utilization affect the trend of uneven subsidence, the simpler space utilization situation (relatively fewer transport lines, construction), the smaller settlement differences and the smaller trend of the uneven subsidence.

InSAR Time-Series Analysis of Land Subsidence under Different Land Use Types in the Eastern Beijing Plain, China

In the Beijing plain, the long-term groundwater overexploitation, exploitation, and the utilization of superficial urban space have led to land subsidence. In this study, the spatial–temporal analysis of land subsidence in Beijing was assessed by using the small baseline subset (SBAS) interferometric synthetic aperture radar (InSAR) technique based on 47 TerraSAR-X SAR images from 2010 to 2015. Distinct variations of the land subsidence were found in the study regions. The maximum annual land subsidence rate was 146 mm/year from 2011 to 2015. The comparison between the SBAS InSAR results and the ground leveling measurements showed that the InSAR land subsidence results achieved a precision of 2 mm. In 2013, the maximum displacement reached 132 and 138 mm/year in the Laiguangying and DongbalizhuangDajiaoting area. Our analysis showed that the serious land subsidence mainly occurred in the following land use types: water area and wetland, paddy field, upland soils, vegetable land, and peasant-inhabited land. Our results could provide a useful reference for groundwater exploitation and urban planning.

Spatiotemporal evolution of land subsidence around a subway using InSAR time-series and the entropy method

The underground railway network of Beijing City, China, which is an important urban infrastructure, has burgeoned with the expansion of the city. However, the influence of subway construction and operation on local subsidence has received minimal attention. By analyzing the Radarsat-2 synthetic aperture radar satellite data, and using persistent scatterer interferometry, we revealed the land subsidence characteristics along the Beijing Subway Line 6. In the context of land subsidence, the expectation (Ex) reflects the overall level of local land subsidence while the entropy (En) reflects the degree of nonuniformity of local land subsidence in time and space. By comparing the changes in Ex and En, we estimated the spatial range of the influence of the subway on local land subsidence. The influenced area was mainly located between 60 m north of the subway line and 80 m south of the subway line. Land subsidence was most strongly altered during subway construction. During operation of the subway, the deformation rates along the subway increased slightly in the first two years and were then stabilized.

Regional Land Subsidence Analysis in Eastern Beijing Plain by InSAR Time Series and Wavelet Transforms

Land subsidence is the disaster phenomenon of environmental geology with regionally surface altitude lowering caused by the natural or man-made factors. Beijing, the capital city of China, has suffered from land subsidence since the 1950s, and extreme groundwater extraction has led to subsidence rates of more than 100 mm/year. In this study, we employ two SAR datasets acquired by Envisat and TerraSAR-X satellites to investigate the surface deformation in Beijing Plain from 2003 to 2013 based on the multi-temporal InSAR technique. Furthermore, we also use observation wells to provide in situ hydraulic head levels to perform the evolution of land subsidence and spatial-temporal changes of groundwater level. Then, we analyze the accumulated displacement and hydraulic head level time series using continuous wavelet transform to separate periodic signal components. Finally, cross wavelet transform (XWT) and wavelet transform coherence (WTC) are implemented to analyze the relationship between the accumulated displacement and hydraulic head level time series. The results show that the subsidence centers in the northern Beijing Plain is spatially consistent with the groundwater drop funnels. According to the analysis of well based results located in different areas, the long-term groundwater exploitation in the northern subsidence area has led to the continuous decline of the water level, resulting in the inelastic and permanent compaction, while for the monitoring wells located outside the subsidence area, the subsidence time series show obvious elastic deformation characteristics (seasonal characteristics) as the groundwater level changes. Moreover, according to the wavelet transformation, the land subsidence time series at monitoring well site lags several months behind the groundwater level change.

Spatiotemporal characteristics of land subsidence in Beijing from small baseline subset interferometric synthetic aperture radar and standard deviational ellipse

Land subsidence in Beijing has occurred since the 1970s. Five major subsidence areas have formed: Dongjiao Ba Lizhuang-Da Jiaoting, Dong Beijiao-Lai Guangying, Changping Shahe-Ba Xianzhuang, Daxing Yufa-Lixian, and Shunyi-Ping Gezhuang. In this study, we investigated Chaoyang, Shunyi, and Tongzhou districts, which have experienced relatively serious subsidence, and obtained land subsidence monitoring results using data from 47 ASAR images obtained between 2004 and 2010 and the small baseline subset interferometric synthetic aperture radar (SBAS InSAR). On this basis, we calculated the spatial distribution center of persistent scatterer points and the eigenellipse to analyze the spatiotemporal characteristics of subsidence in the study area.