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81.
华南地区汛期极端降水的概率分布特征 总被引:16,自引:2,他引:16
利用1960-2005年华南地区71个测站的逐日降水量资料和NCEP/NCAR南半球月平均海平面气压场再分析资料,采用Le Page榆验、广义极值分布等统计诊断方法,研究了华南地区近46 a前汛期(4-6月)和后汛期(7-9月)极端降水的时空变化及概率分布特征.并讨论了南半球澳大利亚高压和马斯克林高压强度指数与华南汛期暴雨日数间年代际变化的关系.结果表明:(1)1992年华南地区降水发生了由减少趋势到增多趋势的突变,降水趋势发生突变后前汛期极端降水量和日极端降水强度有所下降,而后汛期则是显著增强.(2)华南汛期年平均日最大降水量、50 a一遇日最大降水量极值和暴雨日数的空间分布特征相似,即前汛期的空间分布自南向北呈现"低-高-低"的分布趋势,后汛期呈现由沿海到内陆的"高-低"的分布趋势.(3)1992年发生突变后,前、后汛期年平均日最大降水量和年平均暴雨日数显著增加和减少的空间分布基本一致.(4)就年代际变化而言,南半球澳大利亚高压和马斯克林高压的强度变化是华南汛期降水异常的重要气候背景,即当两高压处在同时增强时期时,华南前汛期极端降水处于偏少阶段,后汛期则处于偏多阶段. 相似文献
82.
This paper is a follow-up to a previous paper on the subject of liquefaction potential index (LPI), a parameter that is often used to characterize the potential for surface manifestation of liquefaction at a given site subjected to a given shaking level (represented by a pair of peak ground surface acceleration amax and moment magnitude Mw). In the previous paper by Juang and his coworkers, the LPI was re-calibrated for a piezocone penetration test (CPTU) model, and a simplified model based on LPI was created for computing the conditional probability of surface manifestation of liquefaction (PG). In this paper, the model for this conditional probability PG is extended into a complete framework for assessing the probability of surface manifestation of liquefaction in a given exposure time at a given site subjected to all possible ground motions at all seismic hazard levels. This new framework is formulated and demonstrated with an example site in 10 different seismic regions in the United States. 相似文献
83.
The Seismic Intensity Zoning Map of China(1990)was based on the probabilistic method of seismic hazard analysis.In compiling the map,the characteristics of inhomogeneity of earthquake distribution both in space and time in China are considered sufficiently,and some necessary modifications in the model of seismic hazard analysis are carried out.Based on the analysis of the seismic activity and seismotectonic environment,26 seismic provinces are divided first as the statistical elements of the seismicity analysis; the seismic potential source areas are then divided in the seismic provinces.The 733 potential source areas with various upper limit magnitudes have been divided in the country.According to the reliable time domain of earthquake data with various magnitude intervals,the b values in magnitude-frequency relationship are calculated in the seismic provinces.According to the analysis of the inhomogeneity of seismicity distribution both in space and time,the annual average occurrence rates of the eart 相似文献
84.
85.
This study evaluates the susceptibility of landslides in the Lai Chau province of Vietnam using Geographic Information System
(GIS) and remote sensing data to focus on the relationship between tectonic fractures and landslides. Landslide locations
were identified from aerial photographs and field surveys. Topographic, geological data and satellite images were collected,
processed, and constructed into a spatial database using GIS data and image-processing techniques. A scheme of the tectonic
fracturing of crust in the Lai Chau region was established. Lai Chau was identified as a region with many crustal fractures,
where the grade of tectonic fracture is closely related to landslide occurrence. The influencing factors of landslide occurrence
were: distance from a tectonic fracture, slope, aspect, curvature, soil, and vegetative land cover. Landslide prone areas
were analyzed and mapped using the landslide occurrence factors employing the probability–frequency ratio model. The results
of the analysis were verified using landslide location data and showed 83.47% prediction accuracy. That emphasized a strong
relationship between the susceptibility map and the existing landslide location data. The results of this study can form a
basis stable development and land use planning for the region. 相似文献
86.
利用锦州地区的逐日降水量观测资料对逐日降水量的概率分布进行了统计分析,采用最大似然估计法得到Gamma函数分布的形状参数α和尺度参数β,通过Gamma概率分布模拟观测站点逐日降水的概率分布。结果表明:锦州地区逐日降水频率整体趋势先上升后下降,基本呈对称式分布,降水概率有一定的振荡,个别日会出现远超相邻日期的降水频率,7月21日降水频率最高,在不计微量降水的情况下,最低逐日降水概率有多个日期为0。各季降水频率偏低是造成义县地区干旱的原因之一;北镇夏季平均降水频率最低,但其夏季平均降水量却为锦州地区最高,说明北镇可能易出现较大量级降水或易出现极端降水天气。清明期间降水频率在50%以上、高考期间降水频率在80%以上,符合大众日常对特殊日期降水情况的认知;逐日降水频率可以为公众气象服务提供新的思路。凌海、北镇更容易出现极端降水天气;锦州地区日降水出现小雨天气概率最高,暴雨以上降水概率较低,锦州地区各站极少出现大暴雨以上量级降水,对锦州降水量级预报,尤其是暴雨或大暴雨以上降水量级的预报起到一定的指示作用。 相似文献
87.
88.
F. T. K. Sefe 《水文研究》1988,2(1):75-91
Five aspects of the hydrology of one-day annual minimum flows QIM, have been studied using data from twelve catchments in Malawi. Results indicate that the log-normal distribution can be fitted to all twelve catchments. Four of the rivers studied are intermittent. Application of statistical methods developed in meterology to the dichotomous-transformed data of these catchments revealed that two are ‘flow-dominant’ and the other two are ‘dry-dominant’. Another catchment is entirely dominated by a hydraulic gradient towards the Shire River and Elphant Marsh and so dries up every dry season for considerable periods of time despite the relatively high rainfall in the catchment. QIM, t-days after the date of occurrence of QIM(May), can be better estimated from simple regression than from an empirically determined recession constant. 相似文献
89.
地图信息度量方法的研究 总被引:2,自引:0,他引:2
概率统计方法是最早用于确定地图信息量的方法。但是,由于它的种种不适宜性而受到越来越多的怀疑。本文通过对概率统计方法的分析评价,试图跳出概率统计方法的框框,寻找一种更为有效的测度地图信息量的方法——综合指数法。试验结果表明,这种尝试是十分有效的。 相似文献
90.
SHAO Xuejun XIA Zhenhuan ①Lecturer Deportment of Hydraulic Engineering Tsinghua University Beijing China ②Professor Department of Hydraulic Engineering Tsinghua University Beijing China 《国际泥沙研究》1991,(2)
The random motion of sediment particles suspended in a turbulent flow is studied by means of stochastic process. Results of analysis of particle's frequency response to the random force exerted on the particle due to fluid turbulence suggest that only the lower part of the whole frequency range of the eddy motion will govern the motion of the particle. The mean values of particle velocity and displacement in the vertical direc- tion are calculated and it is found that particle velocity vp- can be decomposed into a mean motion and a velocity fluctuation vp- , where is equal to the fall velocity in tranquil fluid. An Ito^ random differential equation for particle dis- placement Yp is developed, from which a Fokker-Planck equation for the probability density function p(y,t) is derived on the basis of the theory of Markov process, where y denotes the vertical coordinate. The vertical distribution of the particle is thus interrelated to the random motion of the particle. The an effect that a particle will be subject to in the neighborhood or the bottom boundary is taken into consideration and a corresponding Fokker-Planck equation is developed. Analytical solution of the Fok- ker-Planck equation including the lift force effect shows that probability density p(y,t) for the particle displacement has a maximum value at y = H where the perpen- dicular component of the lift force balances the particle gravity. This theoretical result agrees with experimental observations as reported in literature. 相似文献