Holocene changes in tropical wind intensity and rainfall: Evidence from southeast Ghana

Remnants of a fixed aeolian dune ridge occur along the southeast coast of Ghana, just behind the present shoreline. Aeolian sands also cover extensive areas of the Accra Plains. No dunes are present here, the sands mainly occurring as sheets which blanket an early Holocene landscape. The sediments are of mid-Holocene age and were deposited during the interval 4500 B.P.–3800 yr B.P., when the southwesterly winds were stronger than they are at present and much of tropical Africa seems to have been subject to marked aridity. The onset of drier, windier conditions around 4500 yr B.P. brought to an end the more equable climates than had characterized much of West Africa during the earlier Holocene. Aridity, intensified winds, and desert expansion between 4500 and 3800 yr B.P. parallel environmental conditions in tropical continental areas at the height of the Late Pleistocene glaciation.     

Surface wind speed probability distribution in the Southeast Pacific of Marine Stratus and Stratocumulus regions

Probability distributions of surface wind speeds (SWS) near coastal regions are needed for applications such as estimating offshore wind power and ocean surface fluxes and for offshore wind risk assessments. Ocean surface wind speed probability distribution (PDF) is characterized using three-year QuikSCAT and AIRS satellite observations in the southeast Pacific of marine stratus and stratocumulus (MSC) regions. Seasonal variation is removed from wind statistics. It was found that the observed SWS standard deviation has a linear positive relationship with its mean SWS; while the SWS skewness decreases with mean SWS in regimes of strong winds and increases with mean SWS in regimes of weak winds. A simple 1D conceptual model is developed near the Peruvian region, which successfully reproduces the observed relationship between higher moments of SWS and its mean value. The model based physical picture among ocean surface winds, SST, and marine boundary clouds are supported by three-year QuikSCAT surface wind observations and fifteen-year ERA40 re-analysis data. Model sensitive tests suggest that large-scale divergence, and strengths of momentum and cloud fluctuations have significant effects on the ocean SWS-PDF in marine stratus and stratocumulus regions.     

Comparison of probability distributions in extreme value analysis of rainfall and temperature data

Estimation of rainfall and temperature for a desired return period is a prerequisite for planning, design and operation of various hydraulic structures and for evaluation of technical and engineering appraisal of large infrastructure projects. This can be computed through Extreme Value Analysis (EVA) by fitting probability distributions to the annual series of 1-day maximum rainfall, maximum and minimum temperature. This paper details the study on adoption of Extreme Value Type-1, Extreme Value Type-2, 2-parameter Log Normal and Log Pearson Type-3 (LP3) probability distributions in EVA of rainfall and temperature for Hissar. Based on the applicability, standard parameter estimation procedures such as method of moments, maximum likelihood method (MLM) and order statistics approach are used for determination of parameters of distributions. The adequacy on fitting of probability distributions used in EVA of rainfall and temperature is evaluated by goodness-of-fit (GoF) tests, viz. Anderson–Darling and Kolmogorov–Smirnov and diagnostic test using D-index. The GoF and diagnostic tests results suggest the LP3 (MLM) is better suited amongst four probability distributions adopted in EVA of rainfall and temperature for Hissar.     

我国登陆台风影响区地质灾害易发性分析

地质环境脆弱的地区,台风的特大暴雨可以诱发山体滑坡和泥石流等地质灾害,造成严重人员伤亡。本文分析了我国登陆台风影响区域内的地质灾害时空分布特点,利用信息量方法,通过灾害的易发性区划来分析登陆台风影响区地质灾害特征,进而比较台风和非台风影响条件下地质灾害产生的地理条件和信息量差异。分析结果表明,在台风强降雨条件下,地质灾害的触发地质环境条件较非台风降雨触发地质灾害明显降低,地质灾害脆弱性明显增加。     

Selection of the best fit probability distribution in rainfall frequency analysis for Qatar

Natural Hazards - Design rainfall is widely used in urban infrastructure planning and design such as culverts and urban drainage systems. In design rainfall estimation, one of the primary steps is...     

两种数值模式资料的平均海平面气压和地面风速在中国区域的评估

利用中国气象局国家级自动站(2 421个)的观测资料, 分别对2012年的ECMWF(欧洲中期数值预报中心)和JMA(日本气象厅)数值模式资料的平均海平面气压和地面风速在中国地区的适用性进行了对比研究.结果表明:两种数值模式资料均能在一定程度上反映观测资料所具有的时空分布特征, 东部地区的适用性均要高于西部地区. 对于平均海平面气压, 在西南地区JMA比ECMWF资料更接近实际观测; 而在其他地区, 两种数值模式资料都较接近实际观测, 冬季的结果比夏季好. 对于地面风速, 这两种数值模式资料各具优势.在中国东南部地区, JMA相对于ECMWF的地面风速资料更接近实际观测值, 而在中国西部地区, 则相反.就8个时次的年变化而言, ECMWF资料的年变化趋势与观测资料更为一致, 而JMA资料的地面风速大小与观测资料更为接近.     

Comparison of AMSR-2 wind speed and sea surface temperature with moored buoy observations over the Northern Indian Ocean

The Northern Indian Ocean (NIO) is unique due to seasonal reversal of wind patterns, the formation of vortices and eddies which make satellite observations arduous. The veracity of sea surface wind (SSW) and sea surface temperature (SST) products of sun-synchronous AMSR-2 satellite are compared with high-temporal moored buoy observations over the NIO. The two year-long (2013–2014) comparisons reveal that the root-mean-square-error (RMSE) of AMSR-2 SST and SSW is \(<0.4{^{\circ }}\hbox {C}\) and \(<1.5\hbox { ms}^{-1}\), respectively, which are within the error range prescribed for the AMSR-2 satellite (\(\pm 0.8{^{\circ }}\hbox {C}\), \(\pm 1.5\hbox { ms}^{-1})\). The SST–wind relation is analyzed using data both from the buoy and satellite. As a result, the low-SST is associated with low-wind condition (positive slope) in the northern part of the Bay of Bengal (BoB), while low SST values are associated with high wind conditions (negative slope) over the southern BoB. Moreover, the AMSR-2 displayed larger slope for SST–wind relation and could be mainly due to overestimation of SST and underestimation of wind as compared to the buoy. The AMSR-2 SSW exhibited higher error during post-monsoon followed by monsoon season and could be attributed to the high wind conditions associated with intense oceanic vortices. The study suggests that the AMSR-2 products are reliable and can be used in tropical air–sea interactions, meso-scale features, and weather and climate studies.     

渗透性与降雨强度对堆积层滑坡稳定性的影响

本文基于非饱和渗流理论及非饱和土的Fredlund双应力变量强度理论,对一沿岩土接触面滑动的堆积层滑坡模型,分别进行了8种条件下的降雨入渗数值模拟试验,研究了不同土体渗透性及降雨强度对滑坡稳定性的影响。结果表明:(1)堆积层滑坡的稳定性与土体的渗透性有密切关系,在降雨后的短期内,土体渗透性越好,滑面孔隙水压力升高越明显,滑坡的稳定性降低程度越大;(2)降雨期间,埋深较浅的滑面,入渗雨水能够较快到达,对滑坡稳定性的影响较大;(3)在相同的降雨时间内,降雨强度越大,滑坡稳定性降低速率越快;(4)降雨强度影响着滑坡发生的滞后性,在降雨总量一定的条件下,若降雨强度较大,雨停后,滑坡稳定性继续下降的程度较大;(5)降雨总量控制着滑坡的最终稳定性。     

Regional prediction of landslide hazard using probability analysis of intense rainfall in the Hoa Binh province, Vietnam

The main objective of this study is to assess regional landslide hazards in the Hoa Binh province of Vietnam. A landslide inventory map was constructed from various sources with data mainly for a period of 21 years from 1990 to 2010. The historic inventory of these failures shows that rainfall is the main triggering factor in this region. The probability of the occurrence of episodes of rainfall and the rainfall threshold were deduced from records of rainfall for the aforementioned period. The rainfall threshold model was generated based on daily and cumulative values of antecedent rainfall of the landslide events. The result shows that 15-day antecedent rainfall gives the best fit for the existing landslides in the inventory. The rainfall threshold model was validated using the rainfall and landslide events that occurred in 2010 that were not considered in building the threshold model. The result was used for estimating temporal probability of a landslide to occur using a Poisson probability model. Prior to this work, five landslide susceptibility maps were constructed for the study area using support vector machines, logistic regression, evidential belief functions, Bayesian-regularized neural networks, and neuro-fuzzy models. These susceptibility maps provide information on the spatial prediction probability of landslide occurrence in the area. Finally, landslide hazard maps were generated by integrating the spatial and the temporal probability of landslide. A total of 15 specific landslide hazard maps were generated considering three time periods of 1, 3, and 5 years.     

中国天山山区降水空间分布模拟及成因分析

为了研究中国天山山区降水空间分布规律及其形成机理,基于研究区DEM及气象站点数据资料,运用偏最小二乘法和GIS技术建立了山区降水估算模型,并分析其降水成因。结果表明:天山山区年降水具有明显的经度和纬度地带性,西段多于东段,北坡(迎风坡)多于南坡(背风坡);研究区降水在海拔4 000 m以下呈线性增加特征,随后显著减少,在5 500 m左右出现第二极大值带;坡度小于50°时降水与坡度呈显著正相关。在地形抬升条件下,随气温下降和相对湿度上升使降水增加,这也是山区降水形成的必要条件。总体来看,偏最小二乘法可以有效解决降水及各因子间多重相关性问题,模型回归效果较显著,在模拟山区降水方面具有一定适用性。     

黄河三角洲埕岛海域地貌演化及其地质灾害分析

根据多次的调查资料分析,埕岛海域现在的海底上主要存在5种微地貌形态区即冲蚀地貌区、滑动挤压脊和塌陷凹坑地貌区、侵蚀残留岗丘或台地、斑状海底地貌区、粗糙和平滑海底。三角洲特殊的地貌演化结果对海底管线、座底式平台稳定造成很大危害,在构筑物设计和施工过程中应予以重视。     

降雨作用下山区边坡稳定性分析

降雨是诱发边坡失稳破坏的主要原因,本文以坡地水文模型为基础,结合无限边坡稳定计算模型,研究降雨条件下边坡启动的临界降雨条件。通过工程算例表明:降雨量与边坡体稳定系数成反比;滑坡启动的临界降雨量随边坡坡度的增大而减少;随边坡土体内摩擦角的增加而逐渐增加,此分析对降雨型滑坡的研究有借鉴性的意义。     

降雨入渗规律的实测与分析

关于降雨入渗可降低土坡的稳定性的研究很多,其机制也逐渐趋明确。然而,一场降雨对土坡稳定产生影响的入渗雨量计算问题还没有得到很好地解决。Holten等研究者的一些计算入渗量的方法在土坡的实际应用中难以满足精度要求;而一些有限元的边界处理方法则建立在假定的入渗规律基础上,多少存在不足。研究设计了室内降雨入渗土柱试验,在初步揭示降雨入渗过程和规律基础上,探讨了准确反映降雨入渗量的有限元计算方法,并通过数值试验进一步揭示室内试验未能明确的降雨入渗规律。     

基于有效降雨强度和逻辑回归的降雨型 滑坡预测模型

以湖南省张家界市桑植县为研究区,在全面分析近30年降雨及滑坡数据的基础上,对滑坡及滑坡数量与降雨因子的关系开展了统计分析研究。首先确定了区域最佳有效降雨衰减系数,同时分别按滑坡规模、坡度、厚度大小统计了降雨与历史滑坡信息,得出有效降雨强度（I）与持续时间（D）散点图,由此确定各不同概率下诱发滑坡的区域有效降雨强度阈值,并进行了滑坡灾害危险性等级划分。进而,利用部分样本数据进行逻辑回归分析,得到了该研究区的滑坡发生概率预测方程,并给出了降雨强度临界值定量表达式,最后选用实际降雨诱发滑坡事件与未诱发滑坡事件进行对比验证。结果表明,文章所建立的滑坡预测模型准确性较高,预测情况与实际情况比较吻合。     

探讨变雨强条件下的入渗过程及影响因素

以积水条件下Green-Ampt入渗模型为基础,拓展其在变雨强中入渗率和累积入渗量计算形式。结合上述理论基础,选用饱和-非饱和土壤水、热和溶质运移模拟软件Hydrus-1D,探讨了常降雨与变雨强的入渗差异和饱和导水率、土壤类型对变雨强入渗过程的影响。研究表明：相对于常降雨,变雨强更利于雨水入渗,累积入渗量显著增加;其他水力参数不变,饱和导水率越大,入渗率与变雨强随时间变化曲线重合率越高,雨强控制时间越长,累积入渗量相应也越大;其他水力参数作用效果不容忽视,其影响作用可与饱和导水率达到相似效果。正确了解变雨强下入渗过程及影响因素,有助于准确地把握实际降雨入渗情况,对指导水力工程有重要的实际意义。     

Effect of translate speed of typhoon on wind waves

Natural Hazards - Quantitative assessments on the effect of translate speed of typhoons on wind waves were carried out. A WRF-SWAN coupled model that used observed meteorological data was applied...     

Decomposition of wind speed fluctuations at different time scales

Understanding the inherent features of wind speed (variability on different time scales) has become critical for assured wind power availability, grid stability, and effective power management. The study utilizes the wavelet, autocorrelation, and FFT (fast Fourier transform) techniques to analyze and assimilate the fluctuating nature of wind speed data collected over a period of 29–42 years at different locations in the Kingdom of Saudi Arabia. The analyses extracted the intrinsic features of wind speed, including the long-term mean wind speed and fluctuations at different time scales (periods), which is critical for meteorological purposes including wind power resource assessment and weather forecasting. The long-term mean wind speed varied between 1.45 m/s at Mecca station and 3.73 m/s at Taif. The annual variation is the largest (±0.97 m/s) at Taif and the smallest (±0.25 m/s) at Mecca. Similarly, the wind speed fluctuation with different periods was also discussed in detail. The spectral characteristics obtained using FFT reveal that Al-Baha, Najran, Taif and Wadi-Al-Dawasser having a sharp peak at a frequency f = 0.00269 (1/day) retain a more regular annual repetition of wind speed than Bisha, Khamis-Mushait, Madinah, Mecca, and Sharourah. Based on the autocorrelation analysis and FFT results, the stations are divided into three groups: (i) having strong annual modulations (Al-Baha, Najran, Taif and Wadi-Al-Dawasser), (ii) having comparable annual and half-yearly modulations (Bisha, Khamis-Mushait, and Mecca) and (iii) having annual modulation moderately prominent (Madinah and Sharourah).