查看更多>>摘要：Extreme events have become increasingly frequent worldwide which are reflected in diverse changes in the shape of the temperature probability density function.However,few studies have paid attention to the heterogeneity of temperature at the scale of climate zones.Here,we use the ERA5-land data set to explore interdecadal summer temperature changes and the distribution across different climate zones from 1981 to 2019.Comparing the minimum(Tmin)and maximum(Tmax)temperature of 1982-1991 and 2010-2019,the results imply that Tmin and Tmax in summer maintained a notable upward trend over the past 40 years,especially Tmm.The effects of a simple shift toward a warmer climate contributed most to all climate zones,while the standard deviation,skewness and kurtosis had minor effects on extreme temperature except for tropics.Quantile analysis shows that the probability of extreme events in all climate zones is increasing in frequency and intensity,especially Tmin and Tmax in temperate climate zone.Understanding diverse reasons for climate change can assist us with taking different measures to address extreme climate in distinct climate zones.
查看更多>>摘要：Gully morphology is an important part of loess landform research.Along with gully development,the variation of its cross section is the most significant,and it can intuitively reflect the characteristics of the lateral widening of the gully slope.Therefore,in-depth research of the variation of the cross-sectional morphology of the gully is helpful to understanding the development process of the loess gully.Based on the DEMs(Digital Elevation Model)of nine periods of an indoor simulated loess small watershed,this paper studies the evolution model of a complete branch ditch in the watershed using the digital terrain analysis theory and method.Results show that with the development of the gully,the average gradient of the gully slope continuously decreases,and the slope morphology is mostly a concave slope along the slope direction.The degree of downward concave first increases and then gradually tends to be gentle.The gully erosion mode is gradually transformed from downward cutting erosion to lateral erosion.The more mature the gully development,the lower the depth of gully bottom cutting is compared with the width of gully widening.Furthermore,the surface cutting depth tends to be stable and the slope is stable.Then,the transformation law of the slope morphology of the gully cross section with the develop-ment of the gully is studied,and the prediction model of the transformation of the slope morphology of the gully cross section is established by using the Markov chain.The Markov model can better reflect the dynamic change of the slope morphology of the gully cross section,which is of great significance to revealing the external performance and internal mechanism of the gully morphology.
查看更多>>摘要：Rice is an important food crop for human beings.Accurately distinguishing different varieties and sowing methods of rice on a large scale can provide more accurate information for rice growth monitoring,yield estimation,and phenological monitoring,which has significance for the development of modem agriculture.Compact polarimetric(CP)synthetic aperture radar(SAR)provides multichannel information and shows great potential for rice monitoring and mapping.Currently,the use of machine learning methods to build classification models is a controversial topic.In this paper,the advantages of CP SAR data,the powerful learning ability of machine learning,and the important factors of the rice growth cycle were taken into account to achieve high-precision and fine classification of rice paddies.First,CP SAR data were simulated by using the seven temporal RADARSAT-2 C-band data sets.Second,20-two CP SAR parameters were extracted from each of the seven temporal CP SAR data sets.In addition,we fully considered the change degree of CP SAR parameters on a time scale(△CPDoY).Six machine learning methods were employed to carry out the fine classification of rice paddies.The results show that the classification methods of machine learning based on multitemporal CP SAR data can obtain better results in the fine classification of rice paddies by considering the parameters of △CPDoY.The overall accuracy is greater than 95.05％,and the Kappa coefficient is greater than 0.937.Among them,the random forest(RF)and support vector machine(SVM)achieve the best results,with an overall accuracy reaching 97.32％and 97.37％,respectively,and Kappa coefficient values reaching 0.965 and 0.966,respectively.For the two types of rice paddies,the average accuracy of the transplant hybrid(T-H)rice paddy is greater than 90.64％,and the highest accuracy is 95.95％.The average accuracy of direct-sown japonica(D-J)rice paddy is greater than 92.57％,and the highest accuracy is 96.13％.
查看更多>>摘要：The widely spread Carboniferous-Permian coal seam group in southern China has great potential for coalbed methane resources,but the extensively developed tectonically deformed coal seriously restricts its development.Taking the Dahebian block in western Guizhou as the study area,the geological model of coalbed methane reservoirs in the tectonically deformed coal seam group was established,and the spatial distribution pattern of model parameters was clarified by clustering algorithms and factor analysis.The facies model suggests that the main coal body structures in Nos.1,4,and 7 coal seams are cataclastic coal and granulated coal,whereas the No.11 coal seam is dominated by granulated coal,which has larger thicknesses and spreads more continuously.The in situ permeability of primary undeformed coal,cataclastic coal,granulated coal,and mylonitized coal reservoirs are 0.333 mD,0.931 mD,0.146 mD,and 0.099 mD,respectively,according to the production performance analysis method.The property model constructed by facies-controlled modeling reveals that Nos.1,4,and 7 coal seams have a wider high-permeability area,but the gas content is lower;the high-permeability area in the No.11 coal seam is more limited,but the gas content is higher.The results of the self-organizing map neural network and K-means clustering indicate that the geological model can be divided into 6 clusters,the model parameter characteristics of the 6 clusters are summarized by data analysis in combination with 6 factors extracted by factor analysis,and the application of data analysis results in multi-layer coalbed methane co-development is presented.This study provides ideas for the geological modeling in the tectonically deformed coal seam group and its data analysis.
查看更多>>摘要：Quartz-vein-type copper deposits were discover-ed in SN-trend ore-bearing structures in north-west Dayaoshan,Guangxi.Lack of reports on the precise metallogenic age of these deposit has become a bottleneck in metallogenic research in this area.In this study,the quartz vein-type copper mine in Longwei area of Jinxiu was selected as the research object.Fresh illite samples in the fault gouges and ore samples were collected for testing and analysis.Based on the Re-Os isotope dating study,the age of pyrite isochron,belonging to the Caledonian period,was determined to be 417±25 Ma,whereas that of chalcopyrite isochron belonging to the Indosinian period,was found to be 243±18 Ma.Pyrite crystallized consi-derably earlier than chalcopyrite.The obtained EPMA data were combined with rock mineralogical analysis data,Metasomatous mineral pyrite and metasomatic mineral chalcopyrite were identified to have originated from different hydrothermal systems.In the Indosinian period,copper deposits in the Longwei area underwent pyrite crys-tallization,pyrite fragmentation,copper-bearing hydro-thermal filling,and metasomatism,consolidating and forming minerals.The study determined the mineralisation time and ore sources of copper deposits in the Longwei area.The study provides evidence for the existence of Indosinian hydrothermal activities in the north-western Dayaoshan area.
查看更多>>摘要：The deformation structure of soft sediments has always been a research hotspot,which is of great significance for analyzing the tectonic and sedimentary evolution background of a basin,as well as the physical properties of reservoirs.Previous studies have reported that a large number of soft sediment deformation structures are developed in the western part of Liaohe depression.In this study,through core observation and thin section identification,various types of deformation structures are identified in the core samples which are collected from the upper Es4 in the Leijia region,western sag of Liaohe depression,such as liquefied dikes,liquefied breccia,convoluted laminae,annular bedding,synsedimentary faults,vein structures,etc.Based on the characteristics of core structure,single well profile and continuous well profile,combined with the regional background,this study clarifies that the deformation structure of soft sediments in the study area is mainly caused by seismic action.It is found that the permeability and porosity of deformation layers in the study area are higher than those of the undeformation layers,which proves that the deformation structure of soft sediments has a good effect on improving the physical properties of reservoirs.
查看更多>>摘要：Slope variation will significantly affect the characteristics of the wind field around a hill.This paper conducts a large-eddy simulation(LES)on an ideal 3D hill to study the impact of slope on wind field properties.Eight slopes ranging from 10° to 45° at 5° intervals are considered,which covers most conventional hill slopes.The inflow turbulence for the LES is generated by adopting a modified generation method that combines the equilibrium boundary conditions with the Fluent inherent vortex method to improve the simulation accuracy.The time-averaged flow field and the instantaneous vortex structure under the eight slopes are comparatively analyzed.The accuracy of the present method is verified by comparison with experimental data.The slope can affect both the mean and fluctuating wind flow fields around the 3D hill,especially on the hilltop and the leeward side,where a critical slope of 25° can be observed.The fluctuating wind speeds at the tops of steep hills(with slope angles beyond 25°)decrease with increasing slope,while the opposite phenomenon occurs on gentle hills.With increasing slope,the energy of the high-speed descending airflow is enhanced and pushes the separated flow closer to the hill surface,resulting in increased wind speed near the wall boundary on the leeward side and inhibiting the development of turbulence.The vortex shedding trajectory in the wake region becomes wider and longer,suppressing the growth of the mean wind near the wall boundary and enhancing the turbulence intensity.
查看更多>>摘要：Precipitation can shape our climate both in the present and the future.Even though we have made significant advances in studying the mechanisms of millennial-scale climate changes through high-resolution records,we still cannot quantitatively characterize the global spatiotemporal precipitation variations within the Holocene.Therefore,we developed a new approach to integrating data from 349 globally distributed records and climate models to reconstruct regional and global precipitation patterns over the last 12000 years.Our results reveal that precipitation reconstructions can be divided into monsoon-driven and westerly driven patterns.The results suggest that an arid climate was experienced in the late glacial and early Holocene epoch(～12-7.4 cal ka BP),attaining a middle Holocene optimum(～7.4-3.5 cal ka BP),and drier after the middle Holocene.According to our reconstructions,the global precipitation reconstruction increased from the early Holocene until 3.8 cal ka BP and then subsequently decreased.In addition,our reconstruc-tions better reproduce the low-frequency events and extreme precipitation at the millennial scale in the hemispheres,but the performance of the reconstructions in the equatorial Pacific and the Southern Hemisphere of Africa and the Americas is controversial.The resolution of the record and the simulation capability of the climate model remain important means to improve our understanding of past climate change.
查看更多>>摘要：Anthropogenic disturbances associated with the rapid development of coastal cities have drastically influenced the hydrodynamics and sediment transport processes in many large estuaries globally.Lingdingyang Estuary(LE),located in the central and southern part of the Pearl River Delta,southern China with a long history of high-intensity anthropogenic disturbances,was studied to explore the contribution rate and mechanism underlying the alteration in hydrodynamics and sediment transport under each phase of human activity.A state-of-the-art modeling tool(TELEMAC-2D),was used to study the variations in the hydrodynamics and sediment transport,accounting for reclamation-induced shoreline and dredging-induced topography changes.The results indicated that:ⅰ)under the influence of successive land reclamation,the general distribution of the Confluence Hydrodynamic Zone(CHZ)in LE varied from scattered to concentrated,and these zones moved 3-5 km seaward.ⅱ)Large-scale channel dredging weakened the residual flow in LE,decreasing the residual flow in the Inner-Lingding Estuary(ILE)by 62.45％.This was initiated by the enhancement of tidal dynamics through changes in the bottom friction caused by dredging in the ILE.In contrast,massive reclamation decreased the residual flow in the ILE by 17.55％and increased that in the Outer-Lingding Estuary(OLE).ⅲ)Despite disturbances related to land reclamation and dredging,the estuarine jet flow in LE remained a turbulent jet system,and the estuarine jet flow became more asymmetrical.In addition,the position of the estuarine jet source moved 6-13 km seaward.ⅳ)Both reclamation and dredging decreased the SSC in the ILE and increased the SSC in the OLE.Reclamation weakened the SSC in the ILE by 62.19％,whereas dredging enhanced the SSC in the OLE by 49％.Spatially,reclamation resulted in an increase in the SSC near the outlets and a decrease in the SSC in the northern portion of the Western Channel.Dredging mainly increased the SSC in the northern part of the OLE.ⅴ)The increase in the barotropic pressure gradient was the main factor driving the enhancement of the residual flow and SSC near the outlets.Moreover,the southward location of the"artificial outlets"favored the transport of suspended sediments to the OLE,which was one of the primary reasons for the increase in the SSC in the OLE.Finally,the tidal dynamics of the ILE intensified due to massive reclamation and dredging.The findings of this study indicate that hydrodynamics and sediment transport in LE have greatly changed over the last decades,with reclamation and dredging being the crucial drivers.The insights obtained from this study can serve as a reference for the comprehensive management of the Pearl River Estuary and other large estuaries experiencing similar anthropogenic forcing.
查看更多>>摘要：As a hydrocarbon-rich sedimentary basin in China,the Ordos Basin has enormous potential for shale gas resources.The shale of the Upper Carboniferous Benxi Formation is rich in organic matter,however,its palaeoenvironment and organic matter enrichment mode are yet to be revealed.In this study,the geochemical characteristics of the shale of the Benxi Formation in the east-central part of the Ordos Basin were analyzed to investigate its palaeoenvironment.At the same time,the organic matter enrichment modes in different sedimentary facies were compared and analyzed.The results indicate that:1)the shale of the Benxi Formation was mainly deposited on the continental margin and strong terrestrial clastic input;2)the deposition period of the Benxi Formation shale had a hot and humid climate with high palaeoproductivity and local volcanic hydrothermal fluid,and a high sedimentation rate with the strong stagnant environment.The bottom water was in dysoxic conditions and a semi-saline deposition environment;3)multiple factors,such as palaeoproductivity,volcanic hydrothermal,redox conditions,and palaeosalinity interact to influence the enrichment of shale organic matter in Benxi Formation;4)the organic matter enrichment modes of continental,marine-continental transitional,and marine shales can be classified into three types:"production mode","hybrid mode of preservation and production",and"preservation mode",respectively.This study provides a reference for the organic matter enrichment mode,shale gas formation conditions,and core area evaluation in these marine-continental transitional shales,and also offers new guidance for exploration ideas for shale gas in different sedimentary facies.
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