• Title/Summary/Keyword: Method of Independent Storms

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An alternative method for estimation of annual extreme wind speeds

  • Hui, Yi;Yang, Qingshan;Li, Zhengnong
    • Wind and Structures
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    • v.19 no.2
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    • pp.169-184
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    • 2014
  • This paper presents a method of estimation of extreme wind. Assuming the extreme wind follows the Gumbel distribution, it is modeled through fitting an exponential function to the numbers of storms over different thresholds. The comparison between the estimated results with the Improved Method of Independent Storms (IMIS) shows that the proposed method gives reliable estimation of extreme wind. The proposed method also shows its advantage on the insensitiveness of estimated results to the precision of the data. The volume of extreme storms used in the estimation leads to more than 5% differences in the estimated wind speed with 50-year return period. The annual rate of independent storms is not a significant factor to the estimation.

Towards a revised base wind speed map for the United Kingdom

  • Miller, Craig A.;Cook, Nicholas J.;Barnard, Richard H.
    • Wind and Structures
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    • v.4 no.3
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    • pp.197-212
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    • 2001
  • Observations of extreme wind speeds in the United Kingdom from 1970 to 1980, corrected for the influence of upwind ground roughness and topography, have been analysed using the recently-developed "Improved Method of Independent Storms" (IMIS). The results have been used to compile two new maps of base wind speed and to confirm the climatic factors in current use. One map is 'irrespective' of wind direction and the other is 'equally weighted' by direction. The 'equally weighted' map is expected to be more consistently reliable and appropriate for use with the climatic factors for the design of buildings and structures.

Improving the Gumbel analysis by using M-th highest extremes

  • Cook, Nicholas J.
    • Wind and Structures
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    • v.1 no.1
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    • pp.25-42
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    • 1998
  • Improvements to the Gumbel method of extreme value analysis of wind data made over the last two decades are reviewed and illustrated using sample data for Jersey. A new procedure for extending the Gumbel method to include M-th highest annual extremes is shown to be less effective than the standard method, but leads to a method for calibrating peak-over-threshold methods against the standard Gumbel approach. Peak-over-threshold methods that include at least the 3rd highest annual extremes, specifically the modified Jensen and Franck method and the "Method of independent storms" are shown to give the best estimates of extremes from observations.

The Gringorten estimator revisited

  • Cook, Nicholas John;Harris, Raymond Ian
    • Wind and Structures
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    • v.16 no.4
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    • pp.355-372
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    • 2013
  • The Gringorten estimator has been extensively used in extreme value analysis of wind speed records to obtain unbiased estimates of design wind speeds. This paper reviews the derivation of the Gringorten estimator for the mean plotting position of extremes drawn from parents of the exponential type and demonstrates how it eliminates most of the bias caused by the classical Weibull estimator. It is shown that the coefficients in the Gringorten estimator are the asymptotic values for infinite sample sizes, whereas the estimator is most often used for small sample sizes. The principles used by Gringorten are used to derive a new Consistent Linear Unbiased Estimator (CLUE) for the mean plotting positions for the Fisher Tippett Type 1, Exponential and Weibull distributions and for the associated standard deviations. Analytical and Bootstrap methods are used to calibrate the bias error in each of the estimators and to show that the CLUE are accurate to better than 1%.

Experimental study of rainfall spatial variability effect on peak flow variability using a data generation method (자료생성방법을 사용한 강우의 공간분포가 첨두유량의 변동성에 미치는 영향에 대한 실험적 연구)

  • Kim, Nam Won;Shin, Mun Ju
    • Journal of Korea Water Resources Association
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    • v.50 no.6
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    • pp.359-371
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    • 2017
  • This study generated flood time series of ungauged catchments in the Andongdam catchment using a distributed rainfall-runoff model and data generation method, and extracted the peak flows of 50 catchments to investigate the effect of rainfall spatial variability on peak flow simulation. The model performance statistics for three gauged catchments were reasonable for all events. The flood time series of the 50 catchments were generated using distributed and mean rainfall time series as input. The distribution of the peak flow using the mean rainfall was similar or slightly different to that using the distributed rainfall when the distribution of the distributed rainfall was nearly uniform. However, the distribution of the peak flow using the mean rainfall was reduced significantly compared to that using the distributed rainfall when actual storms moved to the top or bottom of the study catchment, or the rainfall was randomly distributed. These cases were 35% of total number events. Therefore, the spatial variability of rainfall should be considered for flood simulation. In addition, the power law relationship estimated using the peak flow of gauged catchments cannot be used for estimating the peak flow of ungauged independent catchments due to latter's significant variation of the peak flow magnitude.

Spatio-Temporal Characteristics of Droughts in Korea: Construction of Drought Severity-Area-Duration Curves (가뭄의 시공간적 분포 특성 연구: 가뭄심도-가뭄면적-가뭄지속기간 곡선의 작성)

  • Kim, Bo Kyung;Kim, Sang Dan;Lee, Jae Soo;Kim, Hung Soo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.1B
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    • pp.69-78
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    • 2006
  • The rainfall depth-area-duration analysis which is used to characterize precipitation extremes for specification of so-called design storms, provides a basis for evaluation of drought severity when storm depth is replaced by an appropriate measure of drought severity. So we propose a method for constructing drought severity-area-duration curves in this study. Monthly precipitation data over the whole Korea are used to compute SPI. Such SPIs are abstracted to several independent spatial components from EOF analysis. Using Kriging method, these spatial components are used to constitute grid-based SPI data set over the whole Korea including Jeju island with $6km{\times}6km$ resolution. After identifying main drought events, the drought severity-area-duration curves for these events over 32-year period of record are finally constructed. As a result, such curves show the similar shape with storm-based curves in the sense that the drought severity (or rainfall depth) is inversely proportional to drought area from the curves, but drought-based curves are different from storm-based curves in the sense that the drought severity decreasing rate with respect to drought area is much less than depth decreasing rate.