Study on the change characteristics of extreme precipitation and its relationship with urbanization in Hubei Province in recent 54 years

Based on the daily precipitation data, as well as population, population composition data of urban and rural areas in Hubei Province from 1961 to 2014, by using methods such as mean separation, least-squares fitting, trend coefficient and climate trend analysis, M-K and cumulative distance test, the characteristics of extreme precipitation and its relationship with urbanization are analyzed from the aspects of spatio-temporal distribution, trend change and local characteristics in recent 54 years. The results show that:(1) For the extreme precipitation events of 95th percentile, extreme precipitation threshold range is from 43.5 to 85.1 mm, and thresholds of most stations are in the range of rainstorm in Hubei. The two high threshold areas are located in Jianghan Plain and east of Hubei, while the low threshold area is located in northwest of Hubei. The highest threshold appears at Wuhan station, and the two lowest thresholds appear at Zhushan and Fangxian station.(2) Extreme precipitation days(D_ep), extreme precipitation(P_ep), extreme precipitation intensity(I_ep), maximum 5 d precipitation(R_{5 d}) and rainfall ratio have distinct regional characteristics in Hubei, although the regional differences for I_ep and R_{5 d} are less than those for D_ep and P_ep. The southern region of southwest of Hubei, eastern and southern region of southeast of Hubei are high incidence areas of extreme precipitation events, and northwest of Hubei is low incidence area.(3) The extreme precipitation index(R) can reflect extreme precipitation intensity. There are obvious interannual differences on the large scale, although the long-term trend is not significant. P_ep, I_ep and rainfall ratio have a weak increasing trend, and R_{5 d} and extreme precipitation frequency have a weak decreasing trend.(4) The urban development speed changed the spatial distribution of R and their local distances, trend coefficients and climate tendencies. With the urbanization in Hubei, the pattern of "rain island effect" has changed. D_ep, P_ep, I_ep, R_{5 d} and vary from obvious north-south difference to obvious east-west difference. D_ep, P_ep, I_ep, and R_{5 d} increased in Jianghan Plain and east of Hubei, but decreased in southwest of Hubei. The number of stations whose trend coefficients pass the significance level test becomes more. The absolute values of climate tendencies are generally increased, while the changes at most of stations are negative.(5) Extreme precipitation in Hubei has obvious urban effect, extreme precipitation thresholds at metropolitan-representative stations with faster urbanization are more than that of the matching small city-representative stations. The interannual variation of average D_ep, P_ep, I_ep, and R_{5 d} of two kind of representative stations are consistent, while I_ep and R_{5 d} at metropolitan-representative stations are generally more, and the trend of extreme precipitation is more obvious.