Temporal/Spatial Characteristics Of Interannual And Interdecadal Anomalies Of Extreme Precipitation In The Pre-flood Period Of South China And Research On Influencing Factors During The Recent 40 Years

Using the NECP/NCAR reanalysis and daily precipitation data of 89 representative stations from 1969～2008, provided by the National Meteorological Information Center, we have investigated the spatial and temporal variable characteristics of extreme precipitation for pre-flood season (April-June) in South China, at the same time, the proper SST index we have defined is applied to forecast extreme precipitation for pre～flood season in South China, at last, Harmonic Analysis are applied to winter sea surface temperature,850hPa circulation field and precipitation field, and then, Pairwise analysis coupled mode of the annual and interdecadal variations among them. The results are summarized as follows:(1)The precipitation intensity, heavy precipitation amount, and rainstorm days, the spatial distribution of which are basically in agreement with the distribution of the total precipitation in South China during the pre-flood season, may well reflect extreme precipitation for pre-flood season in South China.(2)The temporal variation of extreme precipitation indices are of good indicating significance to the area averaged total precipitation, a significant increase in area averaged total precipitation is closely related t o that of heavy precipitation amount, its frequency and rainstorm days since the 1990s for the pre-flood season in South China; the anomalies of extremely heavy precipitation are significantly enhanced since the 1990s.(3)The proper SST index, we have defined, is a good index to forecast extreme precipitation for pre-flood season in South China, has a good negative correlation with annual variation of extreme precipitation in South China, SST index has been lower(higher) than normal years, then next year, extreme precipitation would stronger(weaker) than normal in South China.(4)In the interannual scale, if El Nino(La Nina) phenomenon occurs in winter, then extreme precipitation for pre-flood season (April-June) in South China would be more stronger(weaker), El Nino phenomenon occurs in winter, SST anomalies will be more weaker, with Lasting impact of SST, a strong cyclone system exists In the north of 30°N,in the west of which the Northeast cold air flow transportes to south of 30°N. South China Sea,Western Pacific Region are in he control of anti-cyclonic circulation,West of which,the southwest air flow transports warm and moist air to southern China.Northeast of the previous flows at this intersection, resulting in extreme precipitation above normal in southern China.(5)In the decadal scale,Interdecadal anomalies of the total rainfall for pre-flood season in South China are obviously different from the other extreme precipitation index. Since the early 80s SST of west wind drift region is cooler than normal in winter, the corresponding total precipitation for pre-flood season in South China is below normal,however, Since 1994, SST of west wind drift region is cooler than normal in winter, SST anomalies will be more weaker, with Lasting impact of SST from last winter pre-flood season in South China, Northeast Pacific, controlled by the cyclone, in the southwestern tip of which,east of Hainan Island exists an anti-cyclonic circulation, at the same time,South China, Hainan Island and the Japanese archipelago are in the control of a strong cyclonic circulation, low-level air flow convergence increased, resulting in extreme precipitation for pre-flood season in South China.