ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 40 Issue 7 > 2014,40(7):787-795. DOI:10.7519/j.issn.1000-0526.2014.07.002 Prev Next
Study on Probability Distribution of Warm Season Hourly Rainfall with Γ Distribution
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Abstract:
Climatology and probability distribution of hourly rainfall are very important for the operational probabilistic short duration heavy rainfall forecasts. By adopting the maximum likelihood estimation, the shape parameter α and scale parameter β of 518 stations are obtained with observed warm season (May 1 to September 30) hourly rainfall data from 1991 to 2009, and Γ distribution function of every station is uniquely determined. The fitted Γ distribution and the distribution of relative frequency of observed hourly rainfall are well matched. For stations with maximum and minimum α and β, the probability distribution and the accumulative probability of hourly rainfall exceeds 0.1 mm are analyzed, and the probability distribution exceeds given thresholds are studied. The results show that the correlation coefficient of α and β gets up to 0.975, and highly dependent on the altitudes. Extreme rainfall probability that could not be revealed by observation data is well displayed by Γ distribution. Distributions of observed hourly rainfall are well depicted, and better continuity obtained. The coastal region of South China has the largest probability to have stronger hourly precipitation and the accumulated probabilities of hourly rainfall exceed 10.0 mm, 20.0 mm and 30.0 mm are 8.0%, 2.0% and 0.7%, respectively. Another remarkably high probability area is the intersectional region of Shandong, Jiangsu and Anhui, which is noticeable during the severe convective forecast. The 95% CDF hourly threshold increases from 5.0 mm at the Northwest to 20.0 mm at the Southeast of China with the maximum hourly rainfall threshold located at the south of Guangxi. Both α and β are highly affected by terrain, the relation between α and altitude can be well fitted by an exponential function with the correlation coefficient getting up to 0.709, which indicates the decisive effect of terrain on hourly rainfall distribution.
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