Analysis Of Preciptitation Concentration Degree Changes In Hunan Province

In this paper, the daily precipitation data from 1961 to 2007 of 84 meteorological stations in Hunan province, explore the temporal and spatial variation characteristics of the Precipitation Concentration Degree (PCD) and Precipitation concentration period (PCP) in Hunan province, and use the PCD and PCP determine their role in Hunan flood, the circulation factor of PCD and PCP.Through these studies, conclusions as followed:(1) Interannual variability of annual precipitation, annual PCD and PCP is increasing year by year in Hunan province, both occurred sudden rise in the early 1980s and 1990s.Spatial distribution are apparently decrease from northwest to southeast and northern PCD is most likely abnormal. The relationship between precipitation and PCD,PCP is little in flood season over southwest Hunan and southeast Hunan, the likelihood of floods is relatively small, precipitation of wet year is more concentrating than dry year, and wet year has a greater chance to get flood disasters. WPSH strength and west end of the ridge is the main circulation factor affecting the annual PCD.(2)The precipitation of Hunan became increasingly uneven, and there’s little change in rainfall concentrated time. Spring precipitation and PCD are mutated rise in the 1990s.The spring PCD and PCP has a significant regional difference in the spatial distribution, Northwestern spring precipitation is more concentrated and easy to be abnormal, Southern spring rainfall is uniform and stable. The more concentrated of the spring precipitation, the more easily of the spring floods, and the maximum precipitation occurs later, the flood disaster is more likely to happen. India Burma trough has the greatest influence on spring precipitation.(3)The summer PCD will experience a concentrated to a uniform process in 30 years, summer PCP has a about 32 year period, experienced 4 cycle alternating from less to more. PCD and PCP in summer has a obvious spatial distribution, Northeast and Middle East of Hunan precipitation get a relative concentration, and other regions has a homogeneous distribution of precipitation. Summer PCP has a little change, PCD and PCP in summer are abnormal happening around the Dongting Lake, and both of them are normal in Southwest. The Western Pacific subtropical high is the direct atmospheric circulation that affecting the summer PCD.(4)The fall PCD and PCP annual variation is small, the drought level in autumn showed an increasing trend. Autumn PCD has the best correlation with cold air, the convergence of cold and warm air in the central area of Hunan Province is good for Middle west precipitation.The cold air forces are stronger, the autumn precipitation concentration is larger, and so is the rainfall duration.