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POT Analysis of Precipitation over Japan

Author(s): Shigenobu Tanaka

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Keywords: Generalized pareto distribution; POT; Extreme precipitation; Trend

Abstract: Climate change impact in hydrological phenomena has been great concern in recent years. This study investigates characteristics of recent extreme precipitation in Japan with not only AMS (Annual Maximum Series) but POT (Peaks Over Threshold) of daily precipitation at 155 meteorological observatories. Some of them have been accumulated for more than 115 years. The annual maximum series (AMS) at each observatory fluctuates extensively and most of them show no significant trend. As such all data of 155 observatories were analyzed as a set and also divided in seven regions. The results show that precipitation is not big before 1920’s but become bigger around 1940. Also, the number of events exceeding 100mm/day/observatory has increased from around 1940. This situation may affect statistical tests on time series of precipitation from early 20th century most of which show increasing trend. When data from 1940 are considered, most statistical tests show no significant trend. AMS from 1940 shows no significant trend, but the 50th largest values in Japan show rather stable increase. The results indicate importance of the observation of larger precipitation and not just maxima. Generalized Pareto distribution2) is applied for Peaks Over Threshold of three periods of 25years from 1940. The result shows that the distribution of each period has a long tail and 100 year return level has increased steadily.


Year: 2016

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