Abstract:

 Based on the daily precipitation data at 50 weather stations in the North China from 1957 to 2011, concentration period and concentration degree of extreme precipitation were analyzed and its inhomogeneity was discussed. The results indicate that the number of extreme precipitation is more in the southeast area and less in the northwest of North China. Concentration degree is large in the east and small in the west, namely, extreme precipitation concentrates in the east and disperses in the west. Extreme precipitation mainly appears in the last ten days of July which is the main flood period in the North China. Extreme precipitation and concentration degree are in significantly decreasing trends, while decreasing trend of concentration period is not significant. Extreme precipitation has a close correlation with concentration degree and concentration period. The more extreme precipitation is, the more concentrated extreme precipitation, the later concentration period is, and vice versa. The above relationship is most significant in the Bohai Bay region. Further analysis show that the trends of extreme precipitation, concentration period and concentration degree are in decreasing trends in Beijing-Tianjin-Tangshan regions. The abrupt change of extreme precipitation occurs in the middle of 1990s in these regions. Extreme precipitation reduces and disperses obviously after 1990s, and concentration period is in advance.

Key words:  Extreme precipitation, Concentration period, Concentration degree