2020年7月两次入海江淮气旋爆发性与非爆发性发展特征对比分析

利用高时空分辨率的欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts, ECMWF)对全球气候的第五代大气再分析数据集(European Re-Analyses 5, ERA5),对比分析了2020年7月淮河上游地区的两次江淮气旋过程,并结合海洋—大气—波浪—泥沙耦合模式(Coupled Ocean-Atmosphere-Wave-Sediment Transport modeling system, COAWST)进行敏感性试验,探讨同一气候尺度背景下,高低频大气环流形势和海气耦合作用对江淮气旋的影响。结果表明,低空环流形势的高频变化和海表温度的升高对气旋的大风影响和强度发展有重要作用。低空环流形势中,存在“气旋—反气旋—气旋”环流天气尺度波列,易造成气旋大风叠加增强;海气交互界面的高海表温度加热作用导致的感热和潜热释放通过气旋北部弯曲锋面强烈的上升运动,为气旋发展提供能量,促进气旋入海后爆发性增强。     

Identification of calanco,a badland landform in the northern Apennines,Italy

Calanco (plural, calanchi) is a term widely used in the northern Apennines, Italy, to define a type of badland formed in clayey bedrock. However, no precise geomorphological definition of calanco has been established and a variety of map symbols are used to indicate the presence of calanco landforms. With the aim of developing an improved approach to identifying calanchi, a group of experienced surveyors identified 24 catchments with calanco characteristics among 67 catchments located between Bologna and Faenza in the northern Apennines. The morphology of each catchment was classified using traditional quantitative geomorphic approaches including fieldwork, map interpretation, hypsometric curve construction and computation of the annual sediment yield. Consideration of the parameters produced by these approaches indicated that none was capable of representing the presence of calanchi unequivocally and the basins were grouped into five classes on the basis of number and type of calanco criteria that they met. A characteristic of calanchi that is evident on topographic maps is crenulation of the contour lines and in this study a new topographic parameter was developed to represent the degree of contour crenulation. This parameter, LO/LF, is defined as the ratio of the actual length of a contour line (LO) to the length of the same line smoothed by an algorithm based on a moving average (LF). Calculated values of LO/LF ranged from 1·05 to 1·38. To test whether high values of the contour crenulation parameter were associated with calanchi, LO/LF values were added to other criteria for the five classes of catchment. Class 1 catchments, consisting of 14 of the 24 calanchi catchments identified in the field, displayed all of the criteria defining calanchi, and were characterized by the highest values of LO/LF (mean value 1·27 ± 0·15). It is proposed, therefore, that the contour crenulation ratio (LO/LF) may be useful in identifying the calanco landform. Copyright © 2000 John Wiley & Sons, Ltd.     

Effects of different spatial distributions of physical soil crusts on runoff and erosion on the Loess Plateau in China

The response of runoff and erosion to soil crusts has been extensively investigated in recent decades. However, there have been few attempts to look at the effects of spatial configuration of different soil crusts on erosion processes. Here we investigated the effects of different spatial distributions of physical soil crusts on runoff and erosion in the semi‐arid Loess Plateau region. Soil boxes (1.5 m long × 0.2 m wide) were set to a slope of 17.6% (10°) and simulated rainfall of 120 mm h^?1 (60 minutes). The runoff generation and erosion rates were determined for three crust area ratios (depositional crust for 20%, 33%, and 50% of the total slope) and five spatial distribution patterns (depositional crust on the lower, lower‐middle, middle, mid‐upper, and upper slope) of soil crusts. The reduction in sediment loss (‘sediment reduction’) was calculated to evaluate the effects of different spatial distributions of soil crusts on erosion. Sediment yield was influenced by the area ratio and spatial position of different soil crusts. The runoff rate reached a steady state after an initial trend of unsteadily increasing with increasing rainfall duration. Sediment yield was controlled by detachment limitation and then transport limitation under rainfall. The shifting time of erosion from a transport to detachment‐limiting regime decreased with increasing area of depositional crust. No significant differences were observed in the total runoff among treatments, while the total sediment yield varied under different spatial distributions. At the same area ratio, total sediment yield was the largest when the depositional crust was on the upper slope, and it was smallest when the crust was deposited on the lower slope. The sediment reduction of structural crust (42.5–66.5%) was greater than that of depositional crust (16.7–34.3%). These results provide a mechanistic understanding of how different spatial distributions of soil crusts affect runoff and sediment production. Copyright © 2017 John Wiley & Sons, Ltd.     

Response of fish communities in rivers subjected to a high sediment load

Erosion and sediment yield are a significant problem in the Guadalquivir River basin. Such phenomena are largely driven by a land use devoted to intensive cultivation of olive trees, with a large socioeconomic influence in Andalusia. This sediment overload in rivers causes serious impacts on all fluvial ecosystem components.In this study we assess the chronic effect of sediment yield on fish communities at 104 river sites located in two different sub-catchments – the Bembézar and Guadajoz rivers – both with different lithological composition and erosion rates. Sediment yield was estimated using a semi-quantitative Factorial Score Model (FSM), developed specifically for Spanish rivers. The fish populations of both basins were evaluated in composition and abundances by the study of Fernández-Delgado et al., 2014. The influence of sediment yield on the fish community was analyzed using General Additive Models.The sediment yield was higher in the Guadajoz basin (921 T/Km2 per year) than in Bembézar (701 T/Km2 per year). In the former, fish communities were poorer in both fish density and diversity, with Luciobarbus sclateri as the only substantially present species and a significant relationship between sediment yield and load, and fish density. In contrast, in the Bembézar basin, sediment yield was correlated with total fish density, including Luciobarbus sclateri, Pseudochondrostoma willkommii, Cobitis paludica, Iberochondrostoma lemmingii, Anaecypris hispanica, and Cyprinus carpio. Intermediate values of sediment yield led to maximum densities, while those higher decreased the density of these species.     

GIS‐based modelling of soil erosion processes using the modified‐MMF (MMMF) model in a large watershed having vast agro‐climatological differences

The present study demonstrates a spatially distributed application of a field‐scale annual soil loss model, the modified‐MMF (MMMF), to a large watershed using hydrological routing techniques, remote sensing data and geospatial technologies. In this study, the MMMF model is implemented after incorporating the corrections suggested in recent literature along with appropriate modifications of the model to suit the agro‐climatological conditions prevailing in most parts of India. Sensitivity analysis carried out through an Average Linear Sensitivity approach indicates that the model outputs are highly sensitive to soil moisture (MS), bulk density (BD), effective hydraulic depth (EHD), ground cover (GC) and settling velocity for clay (VS_c). During calibration and validation, the performance evaluation statistics are mostly in the range of very good to satisfactory for both runoff and soil loss at the watershed outlet. Even spatial validation of the results of intermediate processes in the water phase and the sediment phase, although qualitative, seems to be reasonable and rational. Furthermore, the soil erosion severity analysis for different land‐uses existing in the watershed indicates that about 90% of the watershed area, especially that occupied by agricultural lands, is vulnerable to the long‐term effects of soil erosion. Copyright © 2018 John Wiley & Sons, Ltd.     

Turbidity and suspended sediment dynamics in small catchments in the Nepal Middle Hills

The Himalayan environment has, until recently, been perceived to be in a critical state of environmental decline, resulting from rapid population growth and associated land‐use change. Recent research, however, has emphasized the difficulty of developing an objective appraisal of the state of the environment in a region where empirical data are scarce and unstructured and where an understanding of the spatial and temporal dynamics of natural environmental processes remains highly uncertain. This paper presents results from an intensive three‐year project designed to help address the regional empirical deficit, establish detailed baseline environmental data and to gain an insight into storm period and seasonal suspended sediment dynamics. The instrumentation, calibration and analysis of high‐frequency infrared turbidimetric records from a number of small subcatchments in the Nepal Middle Hills are reported. Storm period and seasonal variation in turbidity and suspended sediment are examined and hysteresis patterns explored and explained. A variety of methods to estimate seasonal suspended sediment yield in a mixed land‐use catchment are examined, and found to vary by up to a factor of five. Despite the inherent uncertainty, all estimates of catchment sediment yield are found to be high with respect to erosion plot studies from the local area, and this suggests the importance of riparian and channel erosion as major sediment sources, a finding consistent with other regional studies. Copyright © 2000 John Wiley & Sons, Ltd.     

基于遗传算法优化BP神经网络的玉米遥感估产方法

以内蒙古自治区开鲁县玉米作物为研究对象,将生育期内玉米遥感影像所提取的多种植被指数和实地采样点的测产数据作为训练值,利用BP(back propagation)神经网络和遗传算法优化BP(GA-BP)神经网络估产模型,得出网络预测的玉米产量数值。通过决定系数R 2和均方根误差RMSE,比较实测产量与预测产量之间的精度,BP神经网络模型R^2为0.8452,RMSE(%)为28.37;遗传算法优化BP神经网络模型R^2为0.9850,RMSE(%)为6.70,表明遗传算法优化BP神经网络估产模型具有一定可行性和可信度。     

中国陆相油页岩含油率与总有机碳的响应机理

为了建立稳定可靠的利用油页岩总有机碳预测含油率的模型,揭示中国陆相不同成因类型油页岩含油率与总有机碳的内在关系极其重要。通过不同类型盆地油页岩钻井取心测试的关键参数,结合沉积学、有机地球化学、热模拟等学科技术,探讨油页岩含油率与总有机碳的响应机理。结果表明：不同盆地类型与沉积背景下发育的油页岩含油率与总有机碳质量分数均呈现良好的正相关性（R²=0.81~0.97）;中国陆相油页岩的成因类型进一步划分为5种类型,制约着含油率与总有机碳的内在关系;油页岩的升温加热模拟呈现3个失重阶段（温度<150、300~550、600~750℃）,明确了含油率与总有机碳参数的物理意义;相同类型盆地与沉积背景下形成的油页岩具有相近的母质生源组合,从而具有大致相当的再生烃效率。中国陆相油页岩成因类型的细划、含油率与总有机碳物理意义的明确、油页岩再生烃能力的分析,有助于理解中国陆相油页岩含油率与总有机碳的内在响应关系。     

SHORT COMMUNICATIONS FLEXURAL CAPACITY OF EDGE LOADED ANNULAR FOUNDATIONS

Edge loaded annular foundations have been analysed assuming the soil pressure at the contact to be non-uniform using the lower bound approach of Limit Analysis. Variable fixity at the edges has been allowed and the foundation slab is made to follow the Square yield criterion. Results presented in the form of curves can be readily used to obtain the locations of the yield hinge circles for the given slab and the corresponding collapse load. © 1997 John Wiley & Sons, Ltd.     

气象条件对奶牛产奶量的影响及对策

在分析奶牛产奶量时间和空间分布的基础上,将乌兰浩特市全市产奶量和乌兰哈达奶牛场观测站产奶量与乌兰浩特市气象资料进行相关分析,确定了影响当地牛奶产量的关键气象因子和关键时期。结果表明,温度是当地春秋季节和冬季影响奶牛产奶量的主要限制因子,其次是气压和相对湿度,而降雨量和日照时数的影响不明显。