Browsing by Author "De Michele, Carlo"

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Bivariate frequency analysis of rainfall intensity and duration for urban stormwater infrastructure design
(2017-10-01)
Jun, Changhyun
;
Qin, Xiaosheng
;
Gan, Thian Yew
;
Tung, Yeou-Koung
;
De Michele, Carlo
This study presents a storm-event based bivariate frequency analysis approach to determine design rainfalls in which, the number, intensity and duration of actual rainstorm events were considered. To derive more realistic design storms, the occurrence probability of an individual rainstorm event was determined from the joint distribution of storm intensity and duration through a copula model. Hourly rainfall data were used at three climate stations respectively located in Singapore, South Korea and Canada. It was found that the proposed approach could give a more realistic description of rainfall characteristics of rainstorm events and design rainfalls. As results, the design rainfall quantities from actual rainstorm events at the three studied sites are consistently lower than those obtained from the conventional rainfall depth-duration-frequency (DDF) method, especially for short-duration storms (such as 1-h). It results from occurrence probabilities of each rainstorm event and a different angle for rainfall frequency analysis, and could offer an alternative way of describing extreme rainfall properties and potentially help improve the hydrologic design of stormwater management facilities in urban areas. (C) 2017 Elsevier B.V. All rights reserved.
On the statistical analysis of rainstorm events between historical (1777-1907) and modern (1961-2010) periods in Seoul, Korea
(1970-01-01)
Jun, Changhyun
;
Qin, Xiaosheng
;
Tung, Yeou-Koung
;
De Michele, Carlo
;
防災與水環境研究中心
In this study, an event-based approach for developing precipitation indices of extreme hydrological events was proposed to analyse characteristics of rainstorm events over long-term periods. Statistical properties of hourly rainfall data were summarized from the retrieved rainstorm events between historical (1777-1907) and modern (1961-2010) periods at Seoul rain gauge station, Korea. The trends and variations of rainstorm events reflecting rainfall depth/duration/intensity thresholds and annual maximum rainstorm events with the largest rainfall depths in these two periods were analysed and compared. The study results indicated that, at a 5% significance level, there were differences in the means and variances of the number of rainstorm events and the average rainfall depth/intensity per storm. For the historical period, the average rainfall depth, duration and intensity per storm with total rainfall durations had a temporal linear trend with slopes of 0.011 mm year(-1), 0.027 hr year(-1), and -0.009 mm hr(-1) year(-1), respectively; whereas, a general decreasing trend was detected during the modern period with slopes of -0.218 mm year(-1), -0.076 hr year(-1), and - 0.010 mm hr(-1) year(-1), respectively. In terms of annual maximum rainfall depth, no significant temporal trend was found in the historical period but an increasing trend (with a slope of 0.710 mm year(-1)) was detected for the modern period. This study was the first attempt to investigate the variability of rainfall characteristics in Seoul, Korea with high-resolution historical data dating back to almost 250 years ago, using a storm-event-based concept which defined precipitation indices with a holistic consideration of the number of events and their rainfall depth, duration, and intensity.
Storm event-based frequency analysis method
(2018-06-01)
Jun, Changhyun
;
Qin, Xiaosheng
;
Tung, Yeou-Koung
;
De Michele, Carlo
;
防災與水環境研究中心
In this study, a storm event-based frequency analysis method was proposed to mitigate the limitations of conventional rainfall depth-duration-frequency (DDF) analysis. The proposed method takes the number, rainfall depth, and duration of rainstorm events into consideration and is advantageous in estimation of more realistic rainfall quantiles for a given return period. For the purpose of hydraulics design, the rainfall depth thresholds are incorporated to retrieve the rainstorm events for estimating design rainfalls. The proposed method was tested against the observed rainfall data from 1961 to 2010 at Seoul, Korea and the computed rainfall quantiles were compared with those estimated using the conventional frequency analysis method. The study results indicated that the conventional method was likely to overestimate the rainfall quantiles for short rainfall durations. It represented that the conventional method could reflect rainfall characteristics of actual rainstorm events if longer durations (like 24 hours) were considered for estimation of design rainfalls.