On the statistical analysis of rainstorm events between historical (1777-1907) and modern (1961-2010) periods in Seoul, Korea

Abstract

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.