Climatic Characteristics Of Short-duration Rainfall Events In Hunan Province

Based on the1981-2010self-recording precipitation data at97stations of Hunan Province, analysis the temporal and spatial distribution and annual、season changes for the frequency of short duration heavy precipitation,the Annual、Quarterly lh,3h,12h Maximum hourly precipitation series were established at each rainfall station.The extreme value distribution of each lasted maximum rainfall probability distribution patterns are studied by the Pearson-Ⅲ distribution,Lognormal distribution,Gumbel distribution,Weibull distribution and Kexi distribution methods, Regional distribution derived best fit model, And use the model to estimate the given return period rainfall extremes, further analysis of the regional characteristics of the distribution fitting and precipitation extremes. Look forward to provide evaluation assessment data and the basis for a major engineering design, which caused by rainfall such as floods、landslide and debris flow、city waterlogging and other weather disasters.The results showed that:(1)In recent30years, The frequency of heavy precipitation events of short duration in Hunan showed unobvious increase in the overall trend, which sub-period between1991-2000short duration highest frequency and biggest increase of heavy precipitation events.1h,2h,3h precipitation extremes were unobvious downward trend and4h,5h,6h,12h is unobvious upward trend. Seasonal analysis showed:The frequency of heavy precipitation events of short duration is highest in summer and lowest in autumn, the largest increase in the summer and the minimum increase in autumn; Comparison researches on the frequency and increase of heavy precipitation of the presummer rainy season and second rainy season,both were the former higher than latter flood season. Comparative analysis between day and night, data for nearly30years in Hunan Province from March to November.The frequency of short duration rainfall events in day less than in night and the change trend of frequency is also day less in night by1hour,but day more than in night by3and12hours. The frequency of short duration rainfall events in spring is day less than night,and in summer just the opposite,and in autumn Little difference between them.The increase of1and3duration in spring and autumn, day less than in nights and in summer day is greater than the night.The day and night increase of12hours is the opposite of1h,3h hours. The frequency and increase of heavy precipitation of the presummer rainy season which in day is less in night,and in second rainy season is the opposite.(2)From the regional point of view which the short duration frequency and increase for the last30years heavy precipitation events,the frequency is maximum in Southeastern of Hunan and minimum in Southwest.the increase data is largest in Northwestern and minimum in Southwest. The starting time of the short-time strong rainfall, the regional multi-appeared in the evening to the morning, while most05-08h more concentrated.(3)The frequency of short duration rainfall events beginning time shows bimodal,1hour,3hours often start at5:00-8:00,and12hours at11:00-14:00.(4)Gumbel distribution is the optimal distribution of short duration precipitation extremes in Hunan Province.