• Title, Summary, Keyword: mean annual frequency

Search Result 133, Processing Time 0.034 seconds

Estimation of Design Rainfall by the Regional Frequency Analysis using Higher Probability Weighted Moments and GIS Techniques(I) (고차확률가중모멘트법에 의한 지역화빈도분석과 GIS기법에 의한 설계강우량 추정(I) -동질성의 지역구분 방법을 중심으로-)

  • 이순혁;박종화;류경식;지호근;전택기;신용희
    • Magazine of the Korean Society of Agricultural Engineers
    • /
    • v.43 no.4
    • /
    • pp.57-68
    • /
    • 2001
  • It is matter of common knowledge to give impetus to the water resources development to cope with increasing demand and supply for the water utilization project including agricultural living and industrial water owing to the economic and civilization development in recent years. Regional design rainfall is necessary or the design of the dam reservoir levee and drainage facilities for the development of various kinds of essential waters including agricultural water. For the estimation of the regional design rainfall classification of the climatologically an geographically homogeneous regions should be preceded preferentially This study was mainly conducted to derive the optimal regionalization of the precipitation data which can be classified by the climatologically and geographically homogeneous regions all over the regions except Cheju and Wulreung islands in Korea. A total of 65 rain gauges were used to regional analysis of precipitation. Annual maximum series for the consecutive durations of 1, 3, 6, 12, 24, 36, 48 and 72hr were used for various statistical analysis. Both K-means clustering and mean annual precipitation methods are used to identify homogeneous regions all over the regions. Nine and five homogeneous regions for the precipitation were classified by the K-means clustering and mean annual methods, respectively. Finally, Five homogeneous regions were established by the trial and error method with homogeneity test using statistics of $\chi$$^2$ distribution.

  • PDF

On the Change of Flood and Drought Occurrence Frequency due to Global Warming : 1. Change of Daily Rainfall Depth Distribution due to Different Monthly/Yearly Rainfall Depth (지구온난화에 따른 홍수 및 가뭄 발생빈도의 변화와 관련하여 : 1. 연/월강수량의 변화에 따른 일강수량 분포의 변화분석)

  • Yun, Yong-Nam;Yu, Cheon-Sang;Lee, Jae-Su;An, Jae-Hyeon
    • Journal of Korea Water Resources Association
    • /
    • v.32 no.6
    • /
    • pp.617-625
    • /
    • 1999
  • Global warming has begun since the industrial revolution and it is getting worse recently. Even though the increase of greenhouse gases such as $CO_2$ is thought to be the main cause for global warming, its impact on global climate has not been revealed clearly in rather quantitative manners. However, researches using General Circulation Models(GCMs) has shown the accumulation of greenhouse gases increases the global mean temperature, which in turn impacts on the global water circulation pattern. This changes in global water circulation pattern result in abnormal and more frequent meteorological events such as severe floods and droughts, generally more severe than the normal ones, which are now common around the world and is referred as a indirect proof of global warming. Korean peninsula also cannot be an exception and have had several extremes recently. The main objective of this research is to analyze the impact of global warming on the change of flood and drought frequency. Based on the assumption that now is a point in a continuously changing climate due to global warming, we analyzed the observed daily rainfall data to find out how the increase of annual rainfall amount affects the distribution of daily rainfall. Obviously, the more the annual rainfall depth, the more frequency of much daily rainfall, and vice versa. However, the analysis of the 17 points data of Keum river basin in Korea shows that especially the number of days of under 10mm or over 50mm daily rainfall depth is highly correlated with the amount of annual rainfall depth, not the number of dry days with their correlation coefficients quite high around 0.8 to 0.9.

  • PDF

Secular chang of density, litterfall, phytomass and primary productivity in mongolian oak(quercus mongolica)forest (신갈나무 숲의 林木密度, 落葉量, 植物量 및 1次 純生産量의 經年 變化)

  • Kwak, Toung-Se;Kim, Joon-Ho
    • The Korean Journal of Ecology
    • /
    • v.15 no.1
    • /
    • pp.19-33
    • /
    • 1992
  • The density, litterfall, phytomass, and primary productivity for 7 years in quercus mongolian forest locasted at mt. nambyengsan, pyeongchang-gun, gangwon provance in central part of korean peninsula were estimated quantitatively. at the first year in 1984, a stand had 1, 450 trees/ha in tree density, which was 0.67 of skewness and 0.54 of kurtosis in frequency distribution, however, at the 7th year in 1990, the stand had 1, 133 trees/ha in the density with 22%(or 316 tree/ha)in mortality, which was 1.16 of skewness and 1.89 of kurtosis in the frequency. annual mean litterfall was 5 ton DM/ha, which was composed of 68% of leaves, 17% of branches, 3% of bud scales, 9% of arcons and cups, 0.7% of flowers and others. the phytomass of tree layer for 7 years was gradually increased from 149.7 ton DM/ha at the first year to 188.5 ton DM/ha at the 7th year.annual net productivity for the tree layer studied ranged from 8.76 ton DM/ha.yr-1 to 11.62 ton DM/ha. yr-1 with heavy fluctuation year by year. average annual productivity of the stand of trunk, branches, leaves and roots for 7 years were 4.42, 0.67, 3.85 and 1.29 ton DM/ha.yr-1, respectively. turnover rate of the stand was 6.9% at the first year and 5.6% at the 7th year. such fluctuation of the productivity was caused by the chang of density, mortality, mortality and turnover rate.

  • PDF

Comparison of Annual Maximum Rainfall Series and Annual Maximum Independent Rainfall Event Series (연최대치 계열과 연최대치 독립 호우사상 계열의 비교)

  • Yoo, Chul-Sang;Park, Cheol-Soon
    • Journal of Korea Water Resources Association
    • /
    • v.45 no.5
    • /
    • pp.431-444
    • /
    • 2012
  • This study investigated the differences between annual maximum series and annual maximum independent rainfall event series with relatively short and long rainfall durations. Annual maximum independent rainfall events were selected by applying various IETDs and thresholds to the hourly rainfall data in Seoul for the duration from 1961 to 2010. Annual maximum independent rainfall event series decided were then compared with the conventional annual maximum series. Summarizing the results is as follows. First, the effect of IETD and threshold was not beyond the expected level. For example, as the IETD increases, the frequencies of independent rainfall events decreased similarly in their rate for both with short and long durations. However, as the threshold increases, the frequency of those with rather long durations decreased much higher. Second, The mean rainfall intensity of the independent rainfall events was found to remain constant regardless of their duration. This indicates that the annual maximum rainfall intensity could be found in a rainfall event with longer durations. Lastly, the difference between the annual maximum rainfall series and the annual maximum independent rainfall event series with rather short rainfall durations was found significantly large, which decreases with longer durations. This result indicates that the conventional data analysis method, especially for small basins with short concentration time, could lead an unrealistic design rainfall with little possibility of occurrence.

Characteristics of Atmospheric Stability Index of Airmass thunderstorm day at Busan (부산지역 기단성 뇌우 발생일의 대기안정도지수 특성)

  • Jeon, Byung Il
    • Journal of Wetlands Research
    • /
    • v.5 no.1
    • /
    • pp.29-40
    • /
    • 2003
  • This study was performed to research the relation between airmass thunderstorm and stability index with 12 years meteorological data(1990~2001) at Busan. Also We used the analysed stability indices from University of Wyoming to consider airmass thunderstorm. The frequency of thunderstorm occurrence during 12 years was 156 days(annual mean 13days). The airmass thunderstorm frequency was 14 days, most of those occurrence were summertime(59%). And occurrence hour of airmass thunderstorm was distributed from 1300LST to 2100LST broadly. The highest forecast index for airmass thunderstorm at Busan was K index, the lowest forecast index was SWEAT index. The forecasting of thunderstorms is based primary on the concepts of conditional instability, convective instability, and forced lifting of air near the surface. Instability is a critical factor in severe weather development. Severe weather stability indices can be a useful tool when applied correctly to a given convective weather situation.

  • PDF

A Statistical Study on the Meterorological Disasters in Korea caused by the Typhoons (태풍에 의한 우리나라의 기상재해에 관한 통계적 연구)

  • 설동일;민병언
    • Journal of the Korean Institute of Navigation
    • /
    • v.16 no.4
    • /
    • pp.47-54
    • /
    • 1992
  • The purpose of this study is to provide against to the meteorological disasters in Korea caused by the typhoons by means of the statistical analyses for the relation between the intensities of the typhoons and the meteorological disasters. The data are extracted from the "TYPHOON REPORT OF KOREA" and the "TYPHOON WHITE BOOK" issued by the Central Meteorological Office. The results are summarized as follows : (1) The annual mean frequency and the total number of the typhoon causing the disasters during 30 years (1956∼1985) are 2.2, 65 respectively, and the highest number appears in August followed by September and the third is July. And the degrees of themeteorolgocal disasters are alsio the same order. (2) The more serious disasters occurred by the TS degree typhoons, and the TS degree typhoons occupy the highest frequency. (3) The more serious disasters occurred by the TS degree typhoons, and the TS degree typhoons occupy the highest frequency. (3) The meteorological disaster per typhoon is most severe in August, and the July and September are alike in the degree of the disasters per typhoon. (4) The meteorological disasters are approximately a proportional relation to the intensities of the typhoons. (5) The frequency of the Rain typhoon , Wind typhoon and Rain·Wind typhoon are about 2 : 1: 3 in July, August and September respectively. And the severe disasters occur more frequently by the Rain typhoon than by the Wind typhoon.

  • PDF

Regional Frequency Analysis for Rainfall using L-Moment (L-모멘트법에 의한 강우의 지역빈도분석)

  • Koh, Deuk-Koo;Choo, Tai-Ho;Maeng, Seung-Jin;Trivedi, Chanda
    • The Journal of the Korea Contents Association
    • /
    • v.8 no.3
    • /
    • pp.252-263
    • /
    • 2008
  • This study was conducted to derive the optimal regionalization of the precipitation data which can be classified on the basis of climatologically and geographically homogeneous regions all over the regions except Cheju and Ulreung islands in Korea. A total of 65 rain gauges were used to regional analysis of precipitation. Annual maximum series for the consecutive durations of 1, 3, 6, 12, 24, 36, 48 and 72hr were used for various statistical analyses. K-means clustering mettled is used to identify homogeneous regions all over the regions. Five homogeneous regions for the precipitation were classified by the K-means clustering. Using the L-moment ratios and Kolmogorov-Smirnov test, the underlying regional probability distribution was identified to be the generalized extreme value (GEV) distribution among applied distributions. The regional and at-site parameters of the generalized extreme value distribution were estimated by the linear combination of the probability weighted moments, L-moment. The regional and at-site analysis for the design rainfall were tested by Monte Carlo simulation. Relative root-mean-square error (RRMSE), relative bias (RBIAS) and relative reduction (RR) in RRMSE were computed and compared with those resulting from at-site Monte Carlo simulation. All show that the regional analysis procedure can substantially reduce the RRMSE, RBIAS and RR in RRMSE in the prediction of design rainfall. Consequently, optimal design rainfalls following the regions and consecutive durations were derived by the regional frequency analysis.

Buffeting response of a free-standing bridge pylon in a trumpet-shaped mountain pass

  • Li, Jiawu;Shen, Zhengfeng;Xing, Song;Gao, Guangzhong
    • Wind and Structures
    • /
    • v.30 no.1
    • /
    • pp.85-97
    • /
    • 2020
  • The accurate estimation of the buffeting response of a bridge pylon is related to the quality of the bridge construction. To evaluate the influence of wind field characteristics on the buffeting response of a pylon in a trumpet-shaped mountain pass, this paper deduced a multimodal coupled buffeting frequency domain calculation method for a variable-section bridge tower under the twisted wind profile condition based on quasi-steady theory. Through the long-term measurement of the wind field of the trumpet-shaped mountain pass, the wind characteristics were studied systematically. The effects of the wind characteristics, wind yaw angles, mean wind speeds, and wind profiles on the buffeting response were discussed. The results show that the mean wind characteristics are affected by the terrain and that the wind profile is severely twisted. The optimal fit distribution of the monthly and annual maximum wind speeds is the log-logistic distribution, and the generalized extreme value I distribution may underestimate the return wind speed. The design wind characteristics will overestimate the buffeting response of the pylon. The buffeting response of the pylon is obviously affected by the wind yaw angle and mean wind speed. To accurately estimate the buffeting response of the pylon in an actual construction, it is necessary to consider the twisted effect of the wind profile.

Characterization of Task-weighted Agricultural Dust Exposure of Vineyard Workers

  • Lee, Ki-Young
    • Journal of Environmental Health Sciences
    • /
    • v.36 no.4
    • /
    • pp.264-270
    • /
    • 2010
  • Agricultural workers are often exposed to high levels of dust during field operations. A systematic exposure assessment of annual task-weighted exposure has not been thoroughly examined. The occupational dust exposure in two wine grape vineyards was measured. Exposure levels to total and respirable dust were determined for a 1-year cycle of work. An operation profile including the frequency of tasks was established. The means of total and respirable dust exposure were $1.08\;mg/m^3$ and $0.07\;mg/m^3$, respectively. Based on the exposure for each task and the task frequency, task-weighted mean exposures to total and respirable dust were estimated as $1.115\;mg/m^3$ and $0.079\;mg/m^3$, respectively. The task-weighted exposure was significantly represented by three operations and could be attributed to the exposure frequency rather than the exposure intensity of operations. The measurement of a few of the most frequent tasks may be an alternative method of estimating task-weighted exposure. Agricultural dust exposure can be significantly reduced by targeting those tasks most important to task-weighted dust exposure.

Application of artificial neural network model in regional frequency analysis: Comparison between quantile regression and parameter regression techniques.

  • Lee, Joohyung;Kim, Hanbeen;Kim, Taereem;Heo, Jun-Haeng
    • Proceedings of the Korea Water Resources Association Conference
    • /
    • /
    • pp.170-170
    • /
    • 2020
  • Due to the development of technologies, complex computation of huge data set is possible with a prevalent personal computer. Therefore, machine learning methods have been widely applied in the hydrologic field such as regression-based regional frequency analysis (RFA). The main purpose of this study is to compare two frameworks of RFA based on the artificial neural network (ANN) models: quantile regression technique (QRT-ANN) and parameter regression technique (PRT-ANN). As an output layer of the ANN model, the QRT-ANN predicts quantiles for various return periods whereas the PRT-ANN provides prediction of three parameters for the generalized extreme value distribution. Rainfall gauging sites where record length is more than 20 years were selected and their annual maximum rainfalls and various hydro-meteorological variables were used as an input layer of the ANN model. While employing the ANN model, 70% and 30% of gauging sites were used as training set and testing set, respectively. For each technique, ANN model structure such as number of hidden layers and nodes was determined by a leave-one-out validation with calculating root mean square error (RMSE). To assess the performances of two frameworks, RMSEs of quantile predicted by the QRT-ANN are compared to those of the PRT-ANN.

  • PDF