Probability Distribution of Summer Daily Precipitation in the Huaihe Basin of China Based on Gamma Distribution

The probability distribution of precipitation in the Huaihe basin (HB) is analyzed with the shape and scale parameters of a Gamma distribution. The summer daily precipitation records of 158 meteorological raingauges are applied over the HB during the period of 1980–2007, and the precipitation samples are classified into unconditional rainy days and conditional rainy days which have a dry or wet preceding day over the years. The Kolmogorov-Smirnov (K-S) test and the comparison between the Gamma distribution probability density function and the sample frequency of daily precipitation records of five representative stations are conducted and analyzed. The results show that the HB is a “scale-dominated” region characterized with large scale parameters of the Gamma distribution, where rainfall is likely to exhibit large variability leading to extreme wet or dry conditions. Further analysis shows that the confluence area of Sha River and Ying River within the stream between Wangjiaba dam and Bengbu station, the eastern branch of the Huaihe River (HR) between Bengbu station and the Hongze Lake, and the downstream area below the Hongze Lake, are all the areas with a high probability of large precipitation under the condition that the rainy day has a dry preceding day. The eastern part of the Yishu River watershed and the region near Wangjiaba dam are the center of a high probability of large precipitation under the condition that the rainy day has a wet preceding day. Moreover, the day following a dry preceding day has a greater probability of small rainfall. The probability distribution of summer daily precipitation of the HB is significantly skewed. The probability distribution could be more applicable if the rainy days are preceded by a dry or wet day.