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 Tmin. 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.
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 development 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.
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 modern 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 (ΔCPDoY). 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 ΔCPDoY. 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%.
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.
Quartz-vein-type copper deposits were discovered 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 considerably 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 crystallization, pyrite fragmentation, copper-bearing hydrothermal 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.
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.
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.
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 reconstructions 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.
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.
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.
Overmature continental shale is commonly developed, but few studies have given insight into its pore structure and sorption capacity. Various techniques, including SEM, helium porosity and permeability, N2/CO2 adsorption, MICP, and NMR, were used to detect the pore structure of shale from the Shahezi Formation, Xujiaweizi Fault, Songliao Basin. The excess methane adsorption volumes were measured by the volumetric method and modeled by the Langmuir model. Based on the findings, the most developed pores are intraparticle pores in clay minerals, followed by the dissolution pores in feldspar, but organic pores are uncommon. The selected shales have low helium porosity (mean 1.66%) and ultralow permeability (mean 0.0498 × 10−3μm2). The pore throats are at the nanoscale, and the pore-throat size distributions are unimodal, with most less than 50 nm. The studied shales are characterized by the lower specific surface area (SSA) and pore volume (PV) but the larger average pore diameter. The total SSA is contributed by the micro- and mesopores, while the PV is dominated by meso- and macropores. The pore structures are more complex and controlled by multiple factors, such as mineral compositions and diagenesis, but organic matter is not critical. The maximum absolute adsorption methane volume (VL) is 0.97−3.58 cm3/g (mean 1.90 cm3/g), correlating well with the total SSA, SSA, and pore volume of micropores, which indicates that methane is mainly adsorbed and stored in micropores, followed by mesopores.
Normal-pressure shale gas reservoirs are widely distributed in south-eastern Chongqing and show good potential for resource exploration. This paper reports the organic matter (OM), physical, and pore characteristics, mineral composition, and gas content of representative shale samples from the Upper Ordovician Wufeng Formation and Member 1 of the Lower Silurian Longmaxi Formation (Long 1 Member). Microscopic pores within different shale layers of the Long 1 Member were classified, quantitatively evaluated, and their development mechanisms were systematically studied. We found that OM characteristics, mineral composition, and pore type were the main factors affecting the enrichment and preservation of shale gas. The characteristics of the Long 1 Member are mainly controlled by changes in the sedimentary environment. There are evident differences in total organic carbon content and mineral composition vertically, leading to a variable distribution of pores across different layers. Organic matter abundance controls the degree of OM pore development, while clay minerals abundance control the development of clay mineral-related pores. Total organic carbon content generally controls the porosity of the Long 1 Member, but clay minerals also play a role in OM-poor layers. Pore connectivity and permeability are influenced by the development of pores associated with brittle minerals. We propose a microscopic pore development model for the different layers. Combining geochemical data and this pore development model, layers 1‒4 are considered to be excellent shale gas preservation and enrichment reservoirs. Poor preservation conditions in layers 5‒7 result in high levels of shale gas escape. Layers 8‒9 possess a better sealing condition compared with layers 5‒7 and are conducive to the enrichment and preservation of shale gas, and can thus be used as future potential target strata. This research provides a theoretical basis for exploring and evaluating shale gas potential in the studied region or other complex normal-pressure shale blocks.
It has always been challenging to determine the ancient sedimentary environment and associated energy in deep-buried marine carbonates. The energy represents the hydrodynamic conditions that existed when the carbonates were deposited. The energy includes light and chemical energies in compounds and kinetic energy in currents and mass flow. Deep-buried marine carbonates deposited during the Ordovician depositional period in the eastern Tarim Basin result from a complex interplay of tectonics, sedimentation, and diagenesis. As a result, determining the ancient sedimentary environment and associated energy is complex. The natural gamma-ray spectrometry (GRS) log (from 12 wells) is used in this paper to conduct studies on the sedimentary environment and associated energy in deep-buried marine carbonates. The findings show that the values of thorium (Th), uranium (U), potassium (K), and gamma-ray without uranium (KTh) in a natural GRS log can reveal lithological associations, mineral composition, diagenetic environment, stratigraphic water activity, and ancient climatic change. During the Ordovician, quantitative analysis and determination of sedimentary environment energy are carried out using a comprehensive calculation of natural GRS log parameters in typical wells (penetrating through the Ordovician with cores and thin sections) of well GC4, well GC6, well GC7, and well GC8. The results show that GRS log can determine different lithology associations in typical wells than a sieve residue log. Furthermore, cores and thin sections can be used to validate the determination of lithology associations. Based on the determination of lithology associations, the lithology associations that reflect the sedimentary environment and associated energy can be analyzed in a new approach. Furthermore, the sedimentary environment energy curve derived from a natural GRS log can reveal hydrodynamic fluctuations during depositional periods, which will aid in the discovery of carbonate reservoirs, establishing sequence stratigraphic frameworks, and the reconstruction of sea-level changes in the future.
Sedimentation is a key process affecting wetland sustainability and carbon burial flux. In context of sea level rise, climate change and human activities, further understanding about the sedimentary dynamic in wetland is critical in predicting the landscape evolution or the change in carbon burial flux. In this study, based on the field hydrological observation in a mangrove system in the Nanliu River estuary, we found the net flux of suspended sediment to mangrove is 39−72 kg/m in tidal cycles with Turbidity Maximum Zone (TMZ) forming in surface layer and only is 9−18 kg/m in tidal cycles without TMZ. The higher net flux of suspended sediment to mangrove in tidal cycles with TMZ forming in surface layer is attributed to high SSC in rising tide and intense flocculation in mangrove. The significant discrepancy in sedimentation rate in the mangrove patches also can be explained by the probability of TMZ forming in the surface layer of estuary. In future, rapid sea level rising may lead to the change of TMZ pattern in estuary, which will result in non-negligible variation in sedimentation rate in wetlands. According to the present data of sedimentation rate in wetlands, the fragility of wetlands in river estuary may be miscalculated.
Hydrocarbon exploration in the Dongying Sag is constrained by the development of many Cenozoic transtensional structures with complex patterns and dynamic mechanisms. This study uses seismic interpretation and analog modeling to investigate these transtensional structures. Significant results include dividing these transtensional structures into boundary fault, oblique rifting, and deep strike-slip fault controlled structures, according to the relationships between main and secondary faults. They developed in the steep slope zone, the central sag zone, and the slope zone, respectively. In profile, the transtensional structures formed appear to be semi-flower-like, step-like, or negative-flower-like. In plan-view, they appear to be broom-like, soft-linked, or en-echelon structures. Further, these transtensional structures are controlled by the oblique normal slip of boundary faults, by the oblique extension of sub-sags, and by the later extension of deep strike-slip faults. The geometric deformation of these transtensional structures is controlled by the angles between the regional extension direction and the strike of boundary faults, deep faults, or sub-sags, where a larger angle corresponds to less developed transtensional structures. Further, the transtensional structures in the Dongying Sag were created by multi-phase and multi-directional extensions in the Cenozoic— which is also controlled by pre-existing structures. The strike of newborn secondary faults was determined by the regional extension direction and pre-existing structures.
Crop type mapping using remote sensing is critical for global agricultural monitoring and food security. However, the complexity of crop planting patterns and spatial heterogeneity pose significant challenges to field data collection, thereby limiting the accuracy of remotely sensed crop mapping. This study proposed a new approach for rapidly collecting field crop data by integrating unmanned aerial vehicle (UAV) images with the YOLOv3 (You Only Look Once version 3) algorithm. The impacts of UAV flight altitude and the number of training samples on the accuracy of crop identification models were investigated using peanut, soybean, and maize as examples. The results showed that the average F1-score for crop type detection accuracy reached 0.91 when utilizing UAV images captured at an altitude of 20 m. In addition, a positive correlation was observed between identification accuracy and the number of training samples. The model developed in this study can rapidly and automatically identify crop types from UAV images, which significantly improves the survey efficiency and provides an innovative solution for acquiring field crop data in large areas.
This study employs the regional Climate-Weather Research and Forecasting model (CWRF) to first investigate the primary physical mechanisms causing biases in simulating summer precipitation over the Yangtze River Basin (YRB), and then enhance its predictive ability through an optimal multi-physics ensemble approach. The CWRF 30-km simulations in China are compared among 28 combinations of varying physics parameterizations during 1980−2015. Long-term average summer biases in YRB precipitation are remotely correlated with those of large-scale circulations. These teleconnections of biases are highly consistent with the observed correlation patterns between interannual variations of precipitation and circulations, despite minor shifts in their primary action centers. Increased YRB precipitation aligns with a southward shifted East Asian westerly jet, an intensified low-level southerly flow south of YRB, and a south-eastward shifted South Asian high, alongside higher moisture availability over YRB. Conversely, decreased YRB precipitation corresponds to an opposite circulation pattern. The CWRF control configuration using the ensemble cumulus parameterization (ECP), compared to other cumulus schemes, best captures the observed YRB precipitation characteristics and associated circulation patterns. Coupling ECP with the Morrison or Morrison-aerosol microphysics and the CCCMA or CAML radiation schemes enhances the overall CWRF skills. Compared to the control CWRF, the ensemble average of these skill-enhanced physics configurations more accurately reproduces YRB summer precipitation’s spatial distributions, interannual anomalies, and associated circulation patterns. The Bayesian Joint Probability calibration to these configurations improves the ensemble’s spatial distributions but compromises its interannual anomalies and teleconnection patterns. Our findings highlight substantial potential for refining the representation of climate system physics to improve YRB precipitation prediction. This is notably achieved by realistically coupling cumulus, microphysics, and radiation processes to accurately capture circulation teleconnections. Further enhancements can be achieved by optimizing the multi-physics ensemble among skill-enhanced configurations.
