Spatio-temporal variation characteristics of precipitation extremes in Beijing

To achieve scientific evaluation and understanding the changes in precipitation pattern and the spatiotemporal variation in precipitation extremes for urban areas in a changing environment, we analyzed the spatial and temporal distribution and the change characteristics of the precipitation extremes in Beijing. The statistical results for the storm with different durations from the Heavy Rain Atlases in Beijing and the daily precipitation data (from June to September) from 45 rain-gauged stations over Beijing during 1960-2012 were used in this study. The annual maximum value method and the percentile threshold value method were selected to define the precipitation extremes, and six durations storm (e. g. 10 min, 30 min, 1 h, 6 h, 24 h, and 72 h) and three extreme precipitation indices (frequency, precipitation amount, and contribution ratio) under the two thresholds (95% and 99%). The results showed that: ① The spatial distribution of precipitation extremes in Beijing was affected by the topographic features and urbanization, with some high-value centers of extreme precipitation for these special areas (e. g. urban areas, the interface between the mountainous area and the plain areas), which was consistent with the annual precipitation; ② All the extreme precipitation indices have significant decreasing trends during 1960-2012, with a rate of 0.13/10 a (0.04/10 a) for the frequency of extreme precipitation events, 11.59 mm/10 a (5.28 mm/10 a) for the extreme precipitation amount, and 2%/10 a (1%/10 a) for the contribution ratio of extreme precipitation, respectively, under the 95th (99th) percentile threshold; ③ The changes in the two periods (1960-1985 and 1986-2012) between the urban and suburban areas were different due to the impact of urbanization on extreme precipitation. The frequency of extreme precipitation events in the suburban areas was higher than that of urban areas during the 1960-1985, but the other two indices in the suburban areas were lower than urban areas. However, all the three indices in the urban area were higher than that in suburban areas during the period of 1986-2012.