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91.
The Hurst phenomenon and fractional Gaussian noise made easy 总被引:1,自引:0,他引:1
DEMETRIS KOUTSOYIANNIS 《水文科学杂志》2013,58(4):573-595
Abstract The Hurst phenomenon, which characterizes hydrological and other geophysical time series, is formulated and studied in an easy manner in terms of the variance and autocorrelation of a stochastic process on multiple temporal scales. In addition, a simple explanation of the Hurst phenomenon based on the fluctuation of a hydrological process upon different temporal scales is presented. The stochastic process that was devised to represent the Hurst phenomenon, i.e. the fractional Gaussian noise, is also studied on the same grounds. Based on its studied properties, three simple and fast methods to generate fractional Gaussian noise, or good approximations of it, are proposed. 相似文献
92.
ABSTRACTThe trends in hydrological and climatic time series data of Urmia Lake basin in Iran were examined using the four different versions of the Mann-Kendall (MK) approach: (i) the original MK test; (ii) the MK test considering the effect of lag-1 autocorrelation; (iii) the MK test considering the effect of all autocorrelation or sample size; and (iv) the MK test considering the Hurst coefficient. Identification of hydrological and climatic data trends was carried out at monthly and annual time scales for 25 temperature, 35 precipitation and 35 streamflow gauging stations selected from the Urmia Lake basin. Mann-Kendall and Pearson tests were also applied to explore the relationships between temperature, precipitation and streamflow trends. The results show statistically significant upward and downward trends in the annual and monthly hydrological and climatic variables. The upward trends in temperature, unlike streamflow, are much more pronounced than the downward trends, but for precipitation the behaviour of trend is different on monthly and annual time scales. Furthermore, the trend results were affected by the different approaches. Specifically, the number of stations showing trends in hydrological and climatic variables decreased significantly (up to 50%) when the fourth test was considered instead of the first and the absolute value of the Z statistic for most of the time series was reduced. The results of correlations between streamflow and climatic variables showed that the streamflow in Urmia Lake basin is more sensitive to changes in temperature than those of precipitation. The observed decreases in streamflow and increases in temperature in the Urmia Lake basin in recent decades may thus have serious implications for water resources management under the warming climate with the expected population growth and increased freshwater consumption in this region.
Editor Z. W. Kundzewicz; Associate editor Q. Zhang 相似文献
93.
V. Nixon K. Stewart Hornsby 《International journal of geographical information science》2013,27(9):1289-1308
Geographic objects are characterized by having different durations of existence, or geolifespans. A typology based on the concept of a geolifespan is developed to model variations in the longevity of entities that are stored in geographic information systems. The typology consists of two upper-level classes: Persistent and Ephemeral. The Ephemeral class is composed of three subclasses: Temporary, Transient and Brief. The set of possible transitions between classes in the typology is described, capturing how objects can change from one class to another, e.g., from Temporary to Brief or from Transient to Persistent. A transition sequence models the geolifespan class(es) to which an object belongs over a period of time and captures the evolution of dynamic geographic objects with respect to their longevity. Geolifespan classes are applied to scenarios of spatial change as well as a geosensor network to illustrate their role in modelling geographic dynamics. 相似文献
94.
两种群竞争系统的脉冲收获模型的持续生存和周期解 总被引:1,自引:0,他引:1
考虑了两种群竞争系统的脉冲收获模型。利用比较原理,讨论了含脉冲的竞争系统的持续生存性、周期解的存在性和唯一性、全局渐近稳定性,并给出保持这些性质时脉冲项应满足的先验界。 相似文献
95.
The traditional use of land for food, fuel and wood created cultural landscapes, which are threatened across Europe. The factors which contributed to their endangerment need to be identified to achieve effective preservation of such landscapes. The aim of our study was to identify landscapes with historical persistence in a GIS-based comparative analysis of historical and contemporary maps and the most prominent causes of the past landscape changes, based on stakeholders' perspective. We considered a case study in Romania's Carpathians. Three major land cover types were extracted from maps dating from 1912, 1980 and 2009: built-up, pastures and forests. The historical persistence of all land cover types was poor (<20%) and profound changes were quantitatively confirmed. Large, compact patches of unchanged forests were located in the neighbourhood of a national park. The persistent pastures were situated close to human settlements, and their preservation can be related to local traditional agro-silvo-pastoral management. Although the built-up area has increased over time, the corresponding surfaces are small and consist of scattered patches located around historical monuments. Semi-structured interviews were conducted to investigate stakeholders' perspective. Using cluster analysis five prominent causes of past landscape changes are identified: 'increasing tourism', 'land tenure and social changes', 'land-use intensification', 'post-communist transition', and 'foreign investments'. We join the results of the GIS analysis with those from stakeholders' perspective to gain more insights into the landscape changes. This research offers important information that could be used for the further planning of these valuable cultural landscapes in order to avoid potential conflicts and degradation. 相似文献
96.
The use of key-block theory for the analysis of blocky rock mass structures in mining and civil engineering is well established. Such methods have traditionally been used to analyse the stability of rock blocks at free surfaces only. These methods have also been limited to the analysis of relatively few discontinuities, usually assumed to be infinitely persistent. 相似文献
97.
王宇飞 《地质灾害与环境保护》2010,21(2):40-43,63
喜河水电站坝型为混凝土重力坝,重力坝对地基岩体的抗剪强度有较高的要求。前期勘查成果表明喜河水电站坝址区存在较多的缓倾角结构面,缓倾角结构面的存在是影响坝基抗滑稳定的关键,因此要对坝基作出抗滑稳定性评价。首先要研究坝址区缓倾角结构面的分布规律及连通情况,通过对坝址区缓倾角结构面的综合分析研究提出合理的坝基岩体的综合抗剪强度。 相似文献
98.
利用常规气象资料和NCEP再分析资料,从前期天气背景、大气环流演变及产生持续性强降雨的动力、热力和水汽等条件,分析了2008年6月广西出现的一次持续性强降雨过程。结果发现:这次持续性强降雨过程期间,500hPa环流形势稳定,高空西风小槽呈阶梯状持续下滑影响广西,不断诱发暴雨出现;200hPa广西处于南亚高压东部脊区和高空西风急流出口区右方,风速辐散明显,在高低空急流耦合作用下,华南出现了正反两支垂直环流,广西上空辐合上升运动明显,为强降雨的出现提供了极好的动力条件;南海季风暴发和副热带高压在华南沿海的稳定维持,使得华南低空形成了印度洋和南海两吏水汽通道,为暴雨区上空提供了源源不断的水汽;高温、高湿、高能的热力条件,有利于扰动的形成和对流不稳定能量产生,为广西持续性暴雨提供了必要的能量条件。 相似文献
99.
亚洲中部春夏季大气环流持续性异常与我国东部夏季旱涝的关系 总被引:1,自引:0,他引:1
通过对北半球(20oN以北)1958~2002年 500 hPa月平均高度场各格点的点对点月际相关系数的分析,探讨了环流的持续性。结果表明,亚洲中部上空存在着北半球中高纬度唯一的显著的高度场持续区,它的中心区位于(30oN~50oN, 70oE~110oE),这里正是广袤的青藏高原北坡、蒙古高原及黄土高原地区,一年中各月的持续性有明显的季节变化,冬末春初的2月对3月和3月对4月基本上没有持续性可言;4~5月出现了明显的持续性,相关系数突然增长到0.6;5月对6月的持续性继续增加,相关系数达到0.8。夏季至初秋(6~9月)各个月际稳定地保持着0.8的高相关系数。秋、冬各月持续性逐渐减弱,直至春季降到了最低。将1958~2002年中5~9月的月平均高度距平正、负持续最明显的两个7年的逐月环流和季环流作对比分析,得知在正持续年夏季东亚中纬度大气环流呈“西高东低”型;而负持续年的夏季则是“东高西低”型。它们都具有气候意义的稳定性。相应的,在明显正持续年夏季中国东部降水分布呈“北少南多”;而在明显负持续年则是“北多南少”。在这45年间,夏季亚洲中纬度500 hPa的月高度距平由负持续转为正持续,与中国东部降水由“北多南少”转为“南多北少”是对应的。分区逐日识别500 hPa天气系统的结果表明,正持续年亚洲中纬地区盛行高脊,长江中下游地区多低槽和辐合流型;负持续年则盛行低槽,长江中下游多副高控制和西南流型。揭示了中国夏季发生区域旱涝灾害的两种不同的气候进程和盛行天气过程。这样在5、6月份即可预测东亚夏季或盛夏环流形势与中国的降水趋势。 相似文献
100.
Peter J. Unmack 《Journal of Arid Environments》2001,49(4):653
The purposes of this paper are to document the composition and distribution of fishes in the Alice Springs region of Australia, and discuss constraints on fish persistence in this arid region. Nine native and six exotic species were recorded; most exotics no longer exist. Except in Finke River, only one or no native species were found. Fish survival in the area is ameliorated by the exceptionally broad environmental tolerances and migratory abilities of many species, but ultimately depends upon the effects of geology, geomorphology, and the vagaries in pattern of sediment transport on water persistence. 相似文献