Variation of extreme precipitation during the urbanization of Changsha-Zhuzhou-Xiangtan urban agglomeration

Based on the daily precipitation dataset of 9 weather stations in the Changsha-Zhuzhou-Xiangtan urban agglomeration from 1961to 2012, we use the 95th percentile to define the thresholds of extreme precipitation at the various stations in this agglomeration for spring,summer, autumn and winter, and then assess the variation characteristics of extreme precipitation at all seasons between slowly expanding period and rapidly expanding period of urbanization. The results are as follows. (1) There are no significant spatial differences in threshold, frequency and intensity of extreme precipitation; Synoptic systems that cause extreme precipitation are consistently similar at the various stations.(2) Compared to the slowly expanding period of urbanization, in the rapidly expanding period the extreme precipitation days during spring and summer decreased in the northern stations, but increased in the southern stations. Between slowly and rapidly expanding periods,there are identical variations of extreme precipitation intensity in spring, autumn and winter at the various stations, although there are clear difference in summer in northern and southern parts of the urban agglomeration. (3) From slowly expanding period to rapidly expanding period,distribution of extreme precipitation anomalies at the various stations in the urban agglomeration vary clearly in summer. Summer extreme precipitation anomalies at the stations in the northern urban agglomeration vary from positive to negative, but from positive negative to positivein the southern stations.