中国夏季雨日降水量的概率分布

Probability Distribution of Summer Daily Precipitation in China

利用全国174站夏季逐日降水资料估计了雨日降水量的无条件和有条件概率密度函数,并递推得各站1至20 d内最大日降水量的概率分布及10 d、20 d内最大日降水量≥10 mm、≥25 mm、≥50 mm的概率。主要结果是:在无条件和前一天有雨或无雨条件下雨日降水量Γ分布的形状参数α都小于1,且差别不大,而绝大部分站无条件下的尺度参数β大于前一天无雨条件下的0β而小于前一天有雨条件下的1β;无条件和分条件下,雨日降水量的均值和方差的地理分布都是东南沿海地区大于西北内陆地区,且绝大部分站无条件下的μ、σ2分别大于前一天无雨条件下的μ0、σ20,而小于前一天有雨条件下的1μ、σ21;Γ分布能较准确地逼近前一天无雨和前一天有雨两种条件下雨日降水量的样本频率分布;10 d、20 d内最大日降水量≥10 mm、≥25 mm、≥50 mm概率的地理分布,都是东南沿海地区大于西北内陆地区,与同样等级的样本频率的地理分布非常接近。广西西部、云南东部一带为高值区,安徽南部、江西北部一带为次高值区。

The unconditional and conditional probability density functions of daily precipitation are estimated by use of the 1961-2000 summer daily precipitation data of 174 stations in China, and the probability distributions of maximum daily precipitations, and of the maximum daily precipitation greater than or equal to 10 mm, 25 mm, and 50 mm within 10, and 20 days for each station are derived, respectively. The main results show that the differences of the Gamma distribution shape parameter α of daily precipitation under no condition, and the condition of a wet/dry preceding day at different stations are not too large, and all a are smaller than 1. While the scale parameter β of the F distribution, to the overwhelming majority of stations, the unconditional βis greater than the dry preceding day β0 and less than the wet preceding day day-β1. Both unconditional and conditional μ and σ2 in the southeast coastal region are greater than those in the northwest inland area;and for the overwhelming majority of stations, the unconditional μ are greater than the dry preceding day/.to and less than the wet preceding day μ1 ,and the same to the variance of Fdistribution. Γ distribution can accurately approximate to the sample frequency distributions of daily precipitation under the conditions of a wet or dry preceding day. The probability distributions of the dailymaximum precipitation greater than 10 mm,25 mm,and 50 mm within 10 days,and 20 days in the southeast coastal region are all greater than those in the northwest inland area, respectively, approaching to thegeographic distributions of the sample frequency of the same rainfall order. The high value area of probability lies in the west of Guangxi and the east of Yunnan ,and the secondary high value area in the southof Anhui and the north of Jiangxi.