Change Characteristics of Precipitation Concentration Degree (PCD) and Precipitation Concentration Period (PCP) in the Flood Season in Pi River Valley
淠河流域汛期降水集中度和集中期的变化特征

Precipitation Concentration Degree (PCD) and Precipitation Concentration Period (PCP) could quantificationally represent the spatial-temporal inhomogeneity of the precipitation. Analysis of precipitation concentration in flood season is of great importance to taking precautions against and fighting natural adversities in Pi River Valley. With the daily precipitation data between 1956 and 2010 from 12 rainfall stations in Pi River Valley and the definitions of PCD and PCP, this paper analyzed the temporal and spatial distribution characteristics and change rule of precipitation in flood season during the past 55 years. The results show that the precipitation and PCD in the flood season in Pi River Valley have large variation range. The average precipitation is 611.4mm and the maximum (1089.6mm) is 5.4 times of the minimum (202.7mm). The PCD varies from 0.11 to 0.69 and the average is 0.31. As for the PCP, it varies from 37 to 45 pentads and the average is 40.38. Climatic Trend coefficients of precipitation, PCD and PCP in flood season are 0.182, 0.178 and -0.118 respectively. The increasing trend of PCD in flood season is very significant with a marginal value of 0.10, while the PCP exhibits a non-significant decreasing tendency. This could lead to increasing frequency and intensity of flood and waterlog in Pi River Valley. The increasing jump of precipitation in flood season occurred in 1983 and PCD occurred in 1962. On contrast, there isn't any abrupt change in PCP. The two major periods of precipitation variation in Pi River Valley during the past 55 years are 4 years and 9.5 years respectively and the two major periods of PCD are 7 years and 4 years respectively. As for PCP, the major period is 3 years. Thus it can be seen that the oscillation period of 3-4 years are noticeable in all precipitation, PCD and PCP series. Furthermore, there is 7-10 years periodic oscillation in precipitation and PCD. The relevant analysis indicates that there will be more rainstorms and earlier PCP with larger precipitation and PCD.