Earth Science Malaysia (ESMY)

This study uses the Frequency analysis of the maximum daily and annual rainfall recorded during the period 1976-2020 at eight rain-measuring stations in the Ha’il region: Jubbah (106H-196), Baqa’a (103H-193), Simirah (105H-793), Uqlah Ibn Jibrin (208H-508) and Faydat Ibn Suwaylim (108H-198), Al Ha’it (111H-797), Al Ghazalah (215H-812) and Ha’il (101H-191), currently supervised by the Ministry of Environment, Water and Agriculture (MEWA). These stations were selected due to their locations in the Hail region, which is in great urban development causing an increase in demand for water resources to meet the growing population in urban centers. This paper compares four probability distributions (Normal, Log Normal, Gumbel and Exponential) using the rainfall data recorded in eight rain stations located in Ha’il area. Sets of data cover a period of about 45 years. Therefore, this study aims to estimate the maximum daily and annual rainfall by applying 4-four probability distributions, which are the Normal, the Log-Normal, the Exponential, and the Extreme Values-type 1, using the (Chow) model estimation. Results showed that Gumbel (EV 1) distribution has the least critical values in the tests. Hence, it is considered the best fit distribution for annual rainfall in Simirah and Baq’a. Furthermore, based on the results, it is evident that the exponential distribution is the best in Al Ha’it, Faydat Ibn Suwaylim, Al Ghazalah, Ha’il, and Jubbah. Whilst, the log normal distribution is the best in Al Uqlat. The results also showed that Gumbel (EV 1) distribution has the least critical values in the tests. Thus, it is regarded as the best-fit distribution for the maximum daily rainfall in Simirah and Ha’il, and the normal distribution is considered the best for the rest of the rain stations.