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

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.