Comparison of Probable Maximum Precipitation with Annual Maximum Daily-frequented Rainfall on Hamadan Region

In this paper, the probable maximum precipitation (PMP) has been compared to annual maximum daily-frequented rainfalls in the Hamadan Province. In this regard, the 24-h PMP of 14 meteorological stations of Ghamasiab and Ghara-Chay hydrological basins, situated in the Hamadan and Kirmanshah provinces have been estimated based on the Hershfield method. In each station, the PMP value was compared with the annual maximum daily rainfalls calculated from 2 to 10000 years return periods. The result show that the PMP of region varies from 151 to 485 mm. It has an average of variation of 29% present. The annual maximum daily rainfalls present the coefficient of variations between 22 and 50% (26% on average). These variation increases with return period increasing, especially after 100 years return period. The ratio between the annual maximum daily-frequented rainfalls and the PMP values are vary between 0.12 and 0.50, with an average variation of 14%. This ratio increases with return period increasing. The average regression coefficient between the PMP value and this ratio is different. The best coefficient concern the 10000 years return period annual maximum daily rainfall that is about 0.70. The results also show that the 10000 years (return period) annual maximum daily rainfall is about 50% of the PMP value. These results present a simple methodology for control of PMP estimation, especially in the cases that the sufficient data are not available.