| Land subsidence is an environmental geological phenomenon caused by natural or human factors.Natural factors mainly include crustal movement,volcano,earthquake,soil natural consolidation,etc.Common human factors include the exploitation of underground fluid resources and mineral resources,engineering construction,building and traffic load.With the further advancement of urbanization in the 21 st century,land subsidence caused by overexploitation of groundwater and sustainable large-scale human engineering construction in urban areas will become increasingly serious.In urban areas,land subsidence does not only bring ground elevation loss,but also destroies urban infrastructure and buildings,impacts the operation of transportation facilities and the stability of buildings,affects urban surface runoff and hydrological cycle,increases the risk of urban waterlogging disaster,and seriously restricts the sustainable development of cities.In recent years,Wuhan is at the peak of urban construction.And land subsidence caused by karst collapse,soft soil compression and foundation pit dewatering in engineering construction has been reported.Therefore,it is of great significance to monitor the current situation of land subsidence in Wuhan,explore the evolution law of land subsidence,identify the driving factors of land subsidence and reveal a series of resource and environmental effects caused by land subsidence,in order to cope with the increasingly severe land subsidence and its negative effects under the background of rapid urbanization.The insufficiency of the previous research is mainifested in the following four aspects: the monitoring of land subsidence are mostly not rich enough(short period,small scope),lacks of concrete analysis on spatiotemporal pattern analysis of land subsidence,missing quantitative analysis on the driving factors of land subsidence,and seldom involving the resource and environment effects of land subsidence.In order to make up for the deficiency of the studies existing,this study chooses Wuhan city as the study area,take ALOS PALSAR,Radarsat-2 and Sentinel 1A images as data source and extract the rate and time series of land subsidence in Wuhan city based on advanced DInSAR technology.On this basis,a series of spatial pattern analysis methods are used to study the spatial-temporal patterns of land subsidence.Combined with several factors related to ground subsidence,including geological structure background,groundwater status,ground load,underground space development and engineering construction,two GWR model of land subsidence driving force are established to analyze the leading driving factors in different monitoring periods and different subsidence areas.Finally,GeoDetector is used to detect the influence of land subsidence on urban waterlogging,and the waterlogging scenarios of different rainfall periods in Shahu basin are simulated with InfoWorks ICM.(1)Research on land subsidence monitoring method based on improved D-InSAR.Using multi-temporal Sentinel 1A IW images,conventional D-InSAR method and two improved D-InSAR methods(SBAS-InSAR,PS-InSAR)are used to extract land subsidence information of Wuhan city.The advantages and limitations of three land subsidence monitoring methods are analyzed by comparing them with leveling results.The results show that the conventional D-InSAR method requires less data,and can obtain relatively consistent land subsidence spatial distribution results with the improved D-InSAR method.However,the number of coherent points obtained from the inversion is too small,and the error caused by atmospheric interference in the inversion process is large,so it is difficult to meet the needs of land subsidence mapping of large areas of cities.The spatial distribution of land subsidence rate obtained by SBAS-InSAR method and PS-InSAR method is relatively consistent,but the linear fitting degree is not very high with the leveling survey result.The reason may be that the extraction results of land subsidence and leveling survey result are not well matched in space and time,and the leveling point is not widely distributed and partially destroyed.The spatial distribution of the land subsidence area obtained in this experiment is consistent with previous studies,but the land subsidence rate is lower than previous studies due to the long monitoring period and low cartographic resolution.Through comparison with previous studies,it is also found that the area of the subsidence area in north Shahu Lake keeps expanding.(2)Research on spatial-temporal pattern of land subsidence in Wuhan city.To explore the occurrence and evolution law of ground settlement in Wuhan city,taking multi-temporal ALOS PALSAR images(from 2007 to 2011)and Radarsat-2 images(from 2015 to 2019)as the data source,we extract the average rate of land subsidence and time series.To quantitatively describe spatial and temporal patterns,spatial autocorrelation,hotspot,urban-rural gradient landscape pattern analysis are used.Correlation analysis is applied to explore the correlation between land subsidence and construction factors,rainfall and soft soil.The results show that there is a certain land subsidence in the main urban area of Wuhan city during the two monitoring stages,but the land subsidence rate in most areas is less than-5 mm/yr.The land subsidence has obvious spatial autocorrelation.From 2007 to 2011,the areas with high land subsidence rate are concentrated in Hankou area,the area of Shahu Lake,Baishazhou area,and the Yangtze river coastal area in the north of Shahu Lake.From 2015 to 2019,the areas with high land subsidence rate are concentrated in Hankou area,northern Shahu lake,and Baishazhou area.Land subsidence is relatively serious within 1-3 km gradient within the third circulation line.The proportion of landscape types of land subsidence tends to be close and centralized.Hydrogeological conditions,such as the distribution of carbonate rock belt and soft soil layer,are of great importance to the occurrence of land subsidence.Groundwater extraction,underground construction and related urban construction activities all affect the occurrence of land subsidence,and a large amount of rainfall can alleviate the land subsidence to a certain extent.(3)Research on the driving force of land subsidence in Wuhan city.On the basis of sorting out the influencing factors of land subsidence and combining with the actual situation of Wuhan city,relevant indicators from five aspects including geological structure background,groundwater conditions,ground load,underground space development and engineering construction are selected to establish OLS models and GWR models respectively to identify the driving factors of land subsidence in the main urban area of Wuhan city.By comparing the fitting effects of the two models and analyzing the difference of land subsidence driving factors in different monitoring stages,the spatial non-stationarity between land subsidence and its driving factors is discussed.The results show that the global fitting degree(R2)of the two-stage land subsidence GWR models is significantly higher than that of the OLS models,while the AICc value is lower than that of the OLS models,which indicates that the GWR models have a higher interpretation degree.From 2007 to 2011,the main driving factors of land subsidence in Wuhan main urban area are the large distribution of quaternary and soft soil layers,underground space development and engineering construction.From 2015 to 2019,the wide distribution of quaternary system and engineering construction are the main driving factors of land subsidence in Wuhan city.In addition,the influence of some driving factors on land subsidence is different in space.(4)Hydrological effects and simulation of land subsidence in Wuhan city.Taking the main urban area of Wuhan city as the research area and the main water catchment system as the research unit,the role of land subsidence in the formation of urban waterlogging and its interaction with other waterlogging factors are analyzed with GeoDetector model.On this basis,taking Shahu basin as an example and taking the land subsidence as a single variable,using InforWorks ICM to simulate waterlogging scenarios in different rainfall recurrence periods of 5 years,20 years and 50 years and analyze their differences.Results show that the factor influence of land subsidence rate is only 0.13,but the coupling effect between land subsidence and other influencing factors,the urban waterlogging enhanced obviously,so that the land subsidence is not the dominant factor to urban waterlogging,but urban waterlogging due to interaction between land subsidence and other factors(e.g.,topography,ground permeability)may serious.The simulation results are verified according to the actual waterlogging situation during the rainfall,which proved that the InforWorks ICM model is available.Flood simulation results obtained with or without considering land subsidence are generally consistent,but the hydrological effects is not linear due to the uneven land subsidence locally.Land subsidence mainly influences urban hydrological process by changing topographic features.Urban precipitation and runoff convergence have the characteristics of systematicness,and the change of topographic features may bring about the change of waterlogging in the whole basin system.In the face of the increasingly serious land subsidence in urban areas,the primary condition for preventing and controlling land subsidence is to timely monitor the development status and changing trend of land subsidence and identify its multi-cause mechanism.The hydrological model established considering the impact of land subsidence will make more accurate prediction of urban flood process.This article applies improve D-InSAR method to land subsidence monitoring in Wuhan city,and a series of spatial pattern analysis methods to reveal the occurrence and evolution mechanism.Two type of spatial regression model are used to identify the drive factors and spatial nonstationarity of land subsidence.Hydrological effects of land subsidence in urbanized basin are analyzed and simulated by GeoDetector and InforWorks model.This study further enrich and improve the theory and method system of land subsidence research,which has a certain guiding role for the prevention and control of land subsidence and the the alleviation of negative resource and environmental effects.It is of great significance for the sustainable development of and the well-being of residents. |
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