Application of principal component analysis to understand variability of rainfall

The usefulness of principal component analysis for understanding the temporal variability of monsoon rainfall is studied. Monthly rainfall data of Karnataka, spread on 50 stations for a period of 82 years have been analysed for interseasonal and interannual variabilities. A subset of the above data comprising 10 stations from the coherent west zone of Karnataka has also been investigated to bring out statistically significant interannual signals in the southwest monsoon rainfall. Conditional probabilities are proposed for a few above normal/below normal transitions. A sample prediction exercise for June–July using such a transition probability has been found to be successful.     

A ‘snapshot’ of the evolution of the Uruguay River (Del Plata Basin): the Salto depositional sequence (Pleistocene,Uruguay, South America)

This paper provides sedimentological details of the Salto depositional sequence of western Uruguay, which includes the Salto and the Bellaco Formations. These units are interpreted as evidence, in the Uruguayan landscape, of a Pleistocene forebear of the Uruguay River. The Salto depositional sequence, encompasses two depositional cycles: (a) the lower cycle, represented only by the Salto Formation, with conglomeratic sandstones and sandstones intercalated with pelites and fine sandstones; and (b) the upper cycle, represented by the Salto Formation and the Bellaco Formation, characterized by conglomerates and conglomeratic sandstones with horizontal stratification, discontinuous silicified sandy levels and gypsum–clay bodies. The Salto sequence is characterized by braided river deposits, genetically associated with lacustrine or palustrine and possible aeolian sediments. Cyclic alternations of channelized tractive currents and interchannel contexts are indicated. A possible Pleistocene age for the Salto Formation is discussed, in the light of new and preliminary information (thermoluminescence ages) from the lower cycle. There are several lines of evidence indicating semi-arid conditions during the ‘Salto event’. Comments on regional correlation are provided, as well as the effects of neotectonic processes.     

基于主成分分析法的Q2黄土湿陷特性研究

Q2黄土由于埋藏深,结构相对致密,其湿陷性问题常常被忽视。湿陷系数作为评价黄土湿陷程度的定量指标,其影响因素众多,包括土的含水率、干密度、孔隙比等。由于各因素之间存在一定相关性,所建立的湿陷系数与物理指标之间相关关系往往准确度较低。为降低黄土湿陷指标多重相关性对数据回归分析结果的影响,提高预测精度,以彬州渭化乙二醇项目场地Q2黄土为研究对象,在统计分析场地地层物性指标及湿陷系数与物性单一指标之间相关性的基础上,筛选了7个与湿陷系数相关性较好的指标。采用主成分分析法,通过多元线性回归分析,建立了以累积方差贡献率为基础的Q2黄土湿陷系数计算模型。模型计算值与实测值对比结果表明,该方法有效较低了湿陷系数影响因子之间的多重相关性和相互影响问题,证实了所建立的Q2黄土湿陷系数与独立影响因子之间相关关系的合理性和准确性。     

Application of the principal component analysis on geochemical data: a case study in the basement complex of Southern Ilesa area, Nigeria

The study area occupies a part in southern Ilesa and is located within the schist belt of southwestern Nigeria, which embraces undifferentiated schist, gneisses, and migmatites with pegmatites, schist and epidorite complex, quartzite and quartz schist, granite gneiss, amphibolite, pegmatised schist, granulite, and gneiss. The study is aimed at clarifying the potential source of mineralization dealt with before in regional studies. Sixty-one soil samples were collected and analyzed for identifying these elements: Pb, Fe, Ni, Cd, Cr, Cu, Zn, and Mn. Multivariate analysis was done to obtain the coefficients of principal components from the standardized variables The elemental associations from the principal components analysis that accounted for 85.34% variability of the total variance are: Fe–Mn, Pb–Cr, and Cd–Zn. Comparably, these are equivalent with the previous results in the amphibolites and added the extension of association region to involve the schist and epidorite complex, quartzite, and quartz schist. The metallic association ratio revealed high metallic concentrations and led to the mineralization trend in southern Ilesa.     

Climate downscaling over southern South America for present-day climate (1970-1989) using the MM5 model. Mean,interannual variability and internal variability

This work focuses on evaluating the ability of the MM5 regional model to represent the basic features of present climate over South America. The spatial distribution of seasonal means and the interannual variability, as well as annual cycles for precipitation and near-surface temperature have been evaluated. The internal variability has also been investigated. The analysis has two objectives: one of them is to quantify the dynamic downscaling ability to represent the current climate and the other is to identify critical aspects of the regional climate model in South America in order to interpret the reliability of future projections for the end of the twenty-first century in the A2 scenario of the IPCC Special Report on Emissions Scenarios. In general, the MM5 model is able to reproduce adequately the main general features, seasonal cycle and year-to-year variability of near surface variables over South America. The spatial distribution of temperature is well represented, but some systematic errors were identified, such as an overestimation in central and northern Argentina and an underestimation in the mountainous regions throughout the year. The general structure of precipitation is also well captured by the regional model, although it overestimates the precipitation in the Andean region (specifically in central and southern Chile) in all seasons and underestimates the rainfall over tropical latitudes. The annual cycle of precipitation is adequately represented in the subregions analyzed, but its representation is better over La Plata basin (LPB), Cuyo (CU) and southeastern Pampas (SEP). The annual cycle of mean temperature is well represented, too. The model systematically overestimates the interannual variability of temperature and underestimates the interannual variability of precipitation. From the analyses of interannual and internal variability, as well as the biases, it can be concluded that regardless the season, the simulated precipitation is reliable at subtropical latitudes, Uruguay, southern Brazil and east-central of Argentina, but is less reliable over areas of complex topography. For temperature, the regional model is reliable over subtropical latitudes, Uruguay and the south of Brazil only during winter, but it is less reliable or it is even in the limit of reliability over central and southern Chile all along the year. Therefore, it is concluded that the MM5 model is a useful tool for the generation of regional climate change scenarios and for the evaluation of regional climate change scenarios over southern South America.     

Assessment of precipitation and drought variability in the Weihe River Basin,China

The amount and distribution of precipitation play crucial roles in the occurrence of drought in the Weihe River Basin (WRB), China. Using the precipitation data (1960–2010) of 21 meteorological stations, the spatial and temporal characteristics of short-, medium-, and long-term droughts on 3-, 6-, and 12-month time scales, respectively, were examined using the theory of runs and the Standardized Precipitation Index (SPI). The trends of the drought characteristics were analyzed by a modified Mann-Kendall (MMK) test method. Furthermore, comparative analysis of the SPI at different time scales was conducted. The results showed that (1) the main drought type was moderate drought, which occurred frequently in July and October; (2) the drought intensity and frequency were highest in the 1990s, and the drought severity and drought duration in the northwest was more serious than that in the east; (3) an increasing trend of short droughts appeared mainly in the spring and fall; an increasing trend of medium droughts mainly occurred in the 1990s and that of long-term droughts were mainly presented in the northwest region of the WRB; (4) SPI-3 can better reflect precipitation in the current month, SPI-6 has an advantage in characterizing drought persistence, and SPI-12 performs well in capturing extraordinary droughts; and (5) it was also observed that there is a strong relation between the precipitation distribution and drought zones in the basin, and the drought conditions changed continuously with the seasons depending upon the amount and spatial distribution of precipitation .     

Evaluation of CHIRPS and its application for drought monitoring over the Haihe River Basin,China

To establish the drought index objectively and reasonably and evaluate the hydrological drought accurately, firstly, the optimal distribution was selected from nine distributions (normal, lognormal, exponential, gamma, general extreme value, inverse Gaussian, logistic, log-logistic and Weibull), then the Optimal Standardized Streamflow Index (OSSI) was calculated based on the optimal distribution, and last, the spatiotemporal evolution of hydrological drought based on the OSSI series was investigated through the monthly streamflow data of seven hydrological stations during the period 1961–2011 in Luanhe River basin, China. Results suggest: (1) the general extreme value and log-logistic distributions performed prominently in fitting the monthly streamflow of Luanhe River basin. (2) The main periods of hydrological drought in Luanhe River basin were 148–169, 75–80, 42–45, 14–19 and 8–9 months. (3) The hydrological drought had an aggravating trend over the past 51 year and with the increase in timescale, the aggravating trend was more serious. (4) The lower the drought grade was, the broader the coverage area. As for the Luanhe River basin, the whole basin suffered the mild and more serious drought, while the severe and more serious drought only cover some areas. (5) With the increase in time step, the frequency distribution of mild droughts across the basin tended to be concentrated, the frequency of extreme droughts in middle and upper reaches tended to increase and the frequency in downstream tends to decrease. This research can provide powerful references for water resources planning and management and drought mitigation.     

南沙海区曾母盆地地层系统

曾母盆地是南沙海区研究和勘探程度较高的盆地, 其地层系统一直是建立整个南沙海区地层系统的重要依据.然而由于盆地沉积厚度大和横向相变快等原因, 对曾母盆地的分层方案和地层时代的认识存在很大分歧.为了给曾母盆地甚至南沙海区的油气勘探中地层划分对比和地震剖面的解释提供基础依据, 在搜集整理和分析国外有钻井控制的地震剖面和分层方案的基础上, 提出了一个实用的、便于与南海北部盆地对比的曾母盆地地层划分对比方案.将中海油对南海北部诸盆地制定的一套地层界面编号系统和地矿部广州海洋地质局对曾母盆地地层的命名结合起来, 并根据国外在曾母盆地获得的钻探和联井地震测线资料对界面的时代作了一定调整, 将曾母盆地基底以上的地层划分为4组1群(曾母组、立地组、海宁组、南康组、北康群), 之间由5个重要不整合面(T_g、T₆₀、T₄₀、T₃₂、T₃₀) 相分隔.还将该方案与国内外其他方案进行了对比和讨论, 以供阅读有关资料时参考.为了方便将这套地层系统应用于地震剖面的解释和分析, 用实例显示了同一地层中由于地层相变而造成的地震相的巨大变化, 以及各重要不整合面的特征及其在地震剖面上的表现.      

Tectono-thermal evolution of the Reed Bank Basin,Southern South China Sea

The Reed Bank Basin in the southern margin of the South China Sea is considered to be a Cenozoic rifted basin. Tectono-thermal history is widely thought to be important to understand tectonics as well as oil and gas potential of basin. In order to investigate the Cenozoic tectono-thermal history of the Reed Bank Basin, we carried out thermal modeling on one drill well and 22 pseudo-wells using the multi-stage finite stretching model. Two stages of rifting during the time periods of ∼65.5–40.4 Ma and ∼40.4–28.4 Ma can be recognized from the tectonic subsidence rates, and there are two phases of heating corresponding to the rifting. The reconstructed average basal paleo-heat flow values at the end of the rifting events are ∼60 and ∼66.3 mW/m², respectively. Following the heating periods, this basin has undergone a persistent thermal attenuation phase since ∼28.4 Ma and the basal heat flow cooled down to ∼57.8–63.5 mW/m² at present. In combination with the radiogenic heat production of the sedimentary sequences, the surface heat flow of the Reed Bank Basin ranges from ∼60.4 to ∼69.9 mW/m².     

Paleomagnetism and rock magnetism of the Neoproterozoic Itajaí Basin of the Rio de la Plata craton (Brazil): Cambrian to Cretaceous widespread remagnetizations of South America

A detailed rock magnetic and paleomagnetic study was performed on samples from the Neoproterozoic Itajaí Basin in the state of Santa Catarina, Brazil, in order to better constrain the paleogeographic evolution of the Rio de la Plata craton between 600 and 550 Ma. However, rock magnetic properties typical of remagnetized rocks and negative response in the fold test indicated that these rocks carried a secondary chemical remanent magnetization. After detailed AF and thermal cleaning, almost all samples showed a normal polarity characteristic remanent magnetization component close to the present geomagnetic field. The main magnetic carriers are magnetite and hematite, probably of authigenic origin. The mean paleomagnetic pole of the Itajaí Basin is located at Plat = − 84°, Plong = 97.5° (A95 = 2°) and overlaps the lower Cretaceous segment of the apparent polar wander path of South America, suggesting a cause and effect with the opening of the South Atlantic Ocean. A compilation of remagnetized paleomagnetic poles from South America is presented that highlights the superposition of several large-scale remagnetization events between the Cambrian and the Cretaceous. It is suggested that some paleomagnetic poles used to calibrate the APWP of Gondwana at Precambrian times need to be revised; the indication of remagnetized areas in southern South America may offer some help in the selection of sites for future paleomagnetic investigations in Precambrian rocks.     

沁水盆地中—南部煤储层渗透率主控因素分析

通过对沁水盆地中-南部井下煤层宏观裂隙的观测和统计, 将其按大小和形态特征划分为四级, 并在扫描电镜下对显微裂隙进行了系统描述和测量。在分析渗透率与地应力 (埋深) 、裂隙、储层压力和水文地质条件等相互关系的基础上, 指出影响本区煤储层渗透率的主控因素是地应力 (埋深), 在埋深相似的条件下, 其他因素对参透率起着更重要的作用。     

A high-resolution record of climate variability and landscape response from Kettle Lake,northern Great Plains,North America

A decadal-scale multiproxy record of minerals, pollen, and charcoal from Kettle Lake, North Dakota provides a high-resolution record of climate and vegetation change spanning the entire Holocene from the northern Great Plains (NGP) in North America. The chronology is established by over 50 AMS radiocarbon dates. This record exhibits millennial-scale trends evident in other lower-resolution studies, but with much more detail on short-term climate variability and on the rapidity and timing of major climatic shifts. As a proxy for precipitation, we utilize the rate of endogenic carbonate sedimentation, which depends on groundwater inflow, which in turn depends on precipitation. Independent cluster analyses of mineral and pollen data reveal major Holocene mode shifts at 10.73 ka (ka = cal yr BP), 9.25 ka, and 4.44 ka.The early Holocene, 11.7–9.25 ka, was generally wet, with perhaps a trend to higher evaporation associated with warming temperatures. A switch from calcite to aragonite deposition associated with a severe, but brief drought occurred at 10.73 ka. From 10.73 ka to 9.25 ka, climate was generally humid but punctuated at 100–300 yr intervals by brief droughts, including the most severe drought of the entire Holocene at 9.25 ka. This event was coeval with the 9.3–9.2 ka event in the Greenland ice cores and observed at a number of sites worldwide. In contrast, the prominent 8.2 ka event in Greenland is not remarkable at Kettle Lake. The prominence of the 9.25 event locally in the NGP may be due to a major drawdown and northward retreat of Lake Agassiz at this time, reducing its mesoclimatic effect on the NGP and thrusting the region into an insolation controlled regime.The mid-Holocene, 9.25–4.44 ka, was characterized by great variability in moisture on a multi-decadal scale, with severe droughts alternating with more humid periods. The high abundance of the weedy but drought intolerant Ambrosia generally during the mid-Holocene and specifically during the multi-decadal drought periods is seemingly paradoxical, but can be explained by high interannual variability of moisture overlaid on the multi-decadal variability.The late Holocene, 4.44 ka–present, was also characterized by multi-decadal variability in moisture, but was generally wetter than the mid-Holocene and the magnitude of variability was less. The trends in wet-dry mineral, pollen, and charcoal proxies were similar to the mid-Holocene, but late Holocene mineral-pollen assemblages are distinct from mid-Holocene. The shift to wetter climate in the late Holocene was more gradual than the abrupt shift to arid conditions 9.25 ka, which may explain the asymmetric retreat and readvance of forest along the eastern margin of the NGP.Precipitation variations in the NGP have been linked with Pacific and Atlantic sea-surface temperatures, and mid-Holocene drought in the NGP has been linked with sustained La Niña-like conditions in the Pacific. These linkages may explain the decadal- and millennial-scale variations seen in the NGP, but cause of the prominent century-scale variations remains elusive.     

南美奥连特盆地东部斜坡带构造变形物理模拟

南美奥连特盆地东部斜坡带发育大量与正断层反转活动有关的断背斜构造,也是非常有利的油气聚集区。文章主要应用比例化物理模拟实验方法,以奥连特盆地东部斜坡带为模拟对象,来分析早期正断层的陡缓程度、倾向组合以及断层间距等因素对正断层复活反转过程中断背斜构造形成的影响。模拟结果表明,当早期正断层均向挤压端倾斜时,如果陡倾角正断层更靠近挤压端,则陡、缓正断层都易发生反转,并形成断背斜构造。但当缓倾角正断层更靠近挤压端时,则该断层会吸收绝大部分的挤压量,而相对远离挤压端的陡倾角正断层不易发生反转。当早期正断层倾向相对时,距离挤压端更近的陡倾角正断层会吸收一定的挤压量,从而发生反转并形成背斜构造。而相对远离挤压端的缓倾角正断层是否发生复活反转则主要受断层间距的影响,距离越小越有利于断层反转。上述认识对在奥连特盆地东部斜坡带寻找与早期正断层反转有关的断背斜圈闭具有一定指导意义。     

Response of streamflow to climate variability in the source region of Jhelum River Basin in Kashmir valley,India

Natural Hazards - Successful management of the water resources directly depends on our understanding of the heterogeneity of changing climate and consequent response of annual and seasonal...     

Water quality of the Chhoti Gandak River using principal component analysis,Ganga Plain,India

Chhoti Gandak is a meandering river which originates in the terai area of the Ganga Plain and serves as a lifeline for the people of Deoria district, Uttar Pradesh. It travels a distance of about 250 km and drains into Ghaghara near Gothani, Siwan district of Bihar. It has been observed that people of this region suffer from water-borne health problems; therefore water samples were collected to analyse its quality along the entire length of Chhoti Gandak River.     

Classification and Diagenetic Characteristics of the Cretaceous Sandstones in the Southern Bredasdorp Basin,Offshore South Africa

A systematic petrographic and geochemical studies of 92 representative sandstone samples from exploration wells E-AH1, E-AJ1, E-BA1, E-BB1 and E-D3 in the southern part of the Bredasdorp Basin was undertaken to classify the sandstones as well as unravel the main diagenetic processes and their time relations. Petrographic study shows that the sandstones are largely subarkosic arenite and arkosic litharenite, which have underwent series of diagenetic processes as a result burial, rifting and subsequent uplift. The main diagenetic processes that have affected the reservoir properties of the sandstones are cementation by authigenic clay, carbonate and silica, growth of authigenic glauconite, dissolution of minerals and load compaction. The major diagenetic processes reducing the porosity are calcite cementation in the subarkosic arenite, and compaction and quartz cementation in arkosic litharenite. On the other hand, the formation of secondary porosity due to the partial to complete dissolution of early calcite cement, feldspars and minor grain fracturing has improved the reservoir property of the sandstone to some extent. The clay minerals in the sandstones commonly acts as pore choking cement, which reduces porosity. In general, there is no particular diagenetic process that exclusively controls the type or form of porosity evolution in the sandstones.     

Spatio-temporal variation of groundwater recharge in response to variability in precipitation, land use and soil in Yanqing Basin, Beijing, China

It is important to understand how groundwater recharge responds to precipitation variability in space and time, especially in those areas such as Yanqing Basin (China), where groundwater represents the sole water resource. A simple soil-water balance method is applied for spatio-temporal simulation of groundwater recharge in Yanqing Basin from 1981 to 2000. It was implemented on a monthly time step considering the effects of land use and soil texture. The area-average recharge associated with various land uses and soil textures was then compared with zonal analysis using a geographic information system (GIS). The main findings include: (1) the variation of groundwater recharge follows precipitation changes, either at yearly or seasonal intervals, (2) land use plays a more influential role in groundwater recharge than soil texture in this area, and (3) the water table quickly rises in response to recharge in the shallow parts of the aquifer, while there is a delay of 0.5–1.0?years where the groundwater level is at depth 4–10?m. The application demonstrates how spatio-temporal analysis can be utilized for groundwater-recharge estimation through distributed modeling and GIS.     

Determination of regional soil geochemical baselines for trace metals with principal component regression: A case study in the Jianghan plain,China

The soil geochemical baseline is an important index in environmental assessment. Detailed baseline studies are necessary in large areas with complex geological settings, landforms and soil types. The Jianghan plain, a major industrial and agricultural region located in central China, has a soil geochemical baseline that has yet to be fully defined. The objective of this paper is to study the baseline of Cd, Pb and Zn in the topsoil of the Jianghan plain in a subarea using principal component regression (PCR). A total of 9030 samples were collected from the surface layer, and 2 soil profiles and 2 sedimentary columns were sampled near the Yangtze and Han rivers. Fifty-two elements and two parameters were analyzed. Data processing and the creation of spatial distribution maps of the elements were performed using MapGIS, R and SPSS software. The results show that the distributions of Cd, Pb and Zn are mainly controlled by parent material, drainage system and soil type. The study area is divided into 3 subareas, with factors reflecting the physico-chemical characteristics of the soil using factor analysis (FA). The geochemical baseline model is established in every subarea to predict the Cd, Pb and Zn values using principal component regression analysis (PCR); the exceptional values (as a result of anthropogenic input or mineralization) are distinguished by residuals (γ); and the natural background values and anthropogenic contributions are clearly distinguished. Therefore, the PCR method in these subareas is objective and reasonable, and the conclusion provides effective evidence of exceptional high values for further environmental assessment.