Statistical identification of seismicity phases     

A. Pievatolo  R. Rotondi 《Geophysical Journal International》2008,173(3):942-957

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On the emergence of heavy-tailed streamflow distributions     

《Advances in water resources》2015

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Bivariate flood frequency analysis using the copula function: a case study of the Litija station on the Sava River   总被引：3，自引：0，他引：3       下载免费PDF全文

Mojca Sraj  Nejc Bezak  Mitja Brilly 《水文研究》2015,29(2):225-238

As an alternative to the commonly used univariate flood frequency analysis, copula frequency analysis can be used. In this study, 58 flood events at the Litija gauging station on the Sava River in Slovenia were analysed, selected based on annual maximum discharge values. Corresponding hydrograph volumes and durations were considered. Different bivariate copulas from three families were applied and compared using different statistical, graphical and upper tail dependence tests. The parameters of the copulas were estimated using the method of moments with the inversion of Kendall's tau. The Gumbel–Hougaard copula was selected as the most appropriate for the pair of peak discharge and hydrograph volume (Q‐V). The same copula was also selected for the pair hydrograph volume and duration (V‐D), and the Student‐t copula was selected for the pair of peak discharge and hydrograph duration (Q‐D). The differences among most of the applied copulas were not significant. Different primary, secondary and conditional return periods were calculated and compared, and some relationships among them were obtained. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Dry spells assessment with reference to the maize crop in the Luvuvhu River catchment of South Africa     

《Physics and Chemistry of the Earth》2016

Agricultural productivity in South Africa is negatively affected by drought as a result of frequent periodic dry spells and increasing crop water demands resulting in poor crop development and low yields. Thus, we embarked on this study which aims at investigating dry spell occurrences in relation to growing season of maize in the Luvuvhu River Catchment. Daily rainfall data (1945–2014) from 12 stations which represent the catchment fairly well was utilized in this study. Three consecutive planting dates were staggered based on three consecutive onsets of the rainy season. Dry spells were categorized into three groups: short, medium and long dry spells. The data was then subjected to theoretical distribution fitting using the Anderson–Darling goodness-of-fit test; and probabilities of occurrence were computed using a probabilistic model that best fits the data. Trend analysis was performed on the frequency of dry spells per growing period using the non-parametric Spearman's rank correlation test. Out results indicated high probabilities (≥80%) of short dry spells at all the stations irrespective of the timing of planting. Further analysis revealed that a risk of yield reduction with planting following the first onset of rains was higher than that with planting following the second and third onsets. In order to minimize this risk, farmers can be advised to plant between mid-November to mid-December. Trend analysis indicated no trend for all the various dry spell lengths except for Thohoyandou with a decreasing trend and Sigonde with a weak increasing trend in long dry spells. Such findings can be used to describe drought conditions for improvement of agricultural productivity and food security, in a given area.  相似文献   

半参数p-范极大似然回归   总被引：2，自引：0，他引：2  

潘雄  孙海燕 《测绘学报》2005,34(1):30-34

应用核权函数,在观测为误差单峰、对称的情况下,得到了一元p-范分布的半参数模型的计算公式.详细推导了p已知时一元p-范分布极大似然方程的解算公式,将半参数回归模型应用到极大似然平差的参数估计理论中,得到了一个比较好的算法.最后,构造了两个模拟平差问题,说明了此方法的优越性.  相似文献   

Development of Deltas in Some Danish Watercourses     

Bent Hasholt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):10-16

Hasholt. Bent: Development of Deltas in Some Danish Watercourses. Geografisk Tidsskrift 84: 10–16. Copenhagen, January 1984.

Recurrent sedimentation has been observed in three watercourses in western Jutland where the slope of the water surface diminishes due to human intervention. The river bottom was surveyed by a scuba diver, the bedforms were described, and the grain-size distributions analysed. It is concluded that the sedimentation is due to the development of deltas.  相似文献   

URBAN TRANSPORTATION PLANNING IN CALIFORNIA: AN EVALUATION     

《The Professional geographer》2013,65(2):156-161

California's excellent road system has provided unmatched mobility for most of the state's residents. Recently, however, constraints on construction of high-capacity roads have threatened the future of unrestricted auto use. California's transportation planners have therefore shifted emphasis from expanding the transportation system to increasing its efficiency. No concomitant change has occurred, however, in state legislation or resource allocation. As a result, rather than being an integrated process, transportation planning and implementation are fragmented. This paper examines the origins and implications of this situation and possible remedies for it.  相似文献   

Vertical velocity distributions through and above submerged,flexible vegetation     

《水文科学杂志》2013,58(4):905-920

Abstract

A one-dimensional steady-state model was constructed and used to study vertical profiles of longitudinalvelocities in open channel flows through, and above, submerged vegetation. The eddy viscosity was evaluated by using the analogue of the mixing length theory. The model of water velocity profiles takes into account the surface roughness of the channel bottom and the drag exerted by submerged flexible stems. The verification of the calculated velocity profiles was carried out based on data obtained in laboratory experiments. The proportionality coefficients for the analogue of the mixing length formulae in both layers—within homogenous flexible stems and above them—were determined.  相似文献   

The geographic distribution of small dams in Oregon using ecoregion and landform classification     

Suzanne C. Walther  Amanda L. Reinholtz  W. Andrew Marcus 《自然地理学》2013,34(3):286-301

Abstract

Small dams fragment river landscapes, disrupting channel connectivity and impacting water quality and quantity. Although they impound volumetrically less total water than large dams, the ubiquity of small dams suggests their cumulative impacts could be significant. Documenting the distribution and characteristics of small dams is necessary to understanding and mitigating their impacts. In this study, we compare datasets of small dams in Oregon, compile a new comprehensive dataset, and document geographic variations in small dam distributions between different ecoregions. We used Oregon Water Resources Department dam and Oregon Department of Fish and Wildlife fish passage barrier datasets to compare dam heights and contributing drainage areas between different ecoregions. Over 61% of Oregon’s land area is above one or more small dam. We highlight the location of Oregon’s small dams at valley margins, transition zones between flat plains and mountains, and areas of high population density. Given the hidden nature of small dams, evaluation of small dam impacts using public imagery is not effective. However, knowledge of small dam distributions given their association with landforms can aid in finding unrecorded dams, assessing approaches for evaluating their geomorphic impacts, and informing their management.  相似文献   

中尺度对流系统与东北暴雨的关系   总被引：6，自引：2，他引：4       下载免费PDF全文

袁美英  李泽椿  张小玲  李勋  徐南平 《高原气象》2011,30(5):1224-1231

利用2005-2007年6～8月FY-2C卫星逐30min红外云图资料,对东北及其邻近地区中尺度对流系统（包括椭圆型（MCC型）和持续拉长型（PECS型））进行普查分析,并把中尺度对流系统（MCS）分成3种尺度：MCC（或PECS）、MαCS和MβCS,统计分析了它们的时空分布及其与暴雨的关系。结果表明,MCS主要分布...  相似文献