Maryam Mansuri - irrigation and drainage, Department of irrigation, Science and research branch,Islamic Azad University, Tehran, Iran
kazem khosravi - Professional in Water & Soil at Jihad Keshavarzi(Agricultural Crusade) of fars Instructor in Azad Islamic

Introduction:Probable maximum precipitation is the quantity of precipitation which occurs probably in a station, region or aquiferous zone. Probable maximum precipitation is one of the most important factors to assess probable maximum flood, and is very important because main hydraulic structures such as dams are designed and instructed according to it. An accurate assessment of probable maximum precipitation has a significant role to achieve desirable level of security and to reduce expenses of such these plans.Material and method:In this research, the maximum precipitation is calculated statistically during 24 hours by means of some data including maximum precipitation during 24 hours in 16 stations inside and outside of Fars aquiferous zone. This data is collected among Stations of Meteorology Organization and Ministry of Power during a 25-year period.Result and discussion:Studies showed that probable maximum precipitation during 24 hours is 4.17 times more than maximum observed precipitation during 24 hours along the statistical period. A comparison between the PMP amounts during 24 hours and monthly and annual maximum precipitation shows that the maximum probable precipitation is respectively 1.44 and 0.74 times more than observed monthly and annual maximum precipitation during a statistical period. The statistical assessed quantities have not algebraic and determination base and stand on some parameters such as km coefficient and standard deviation. As km coefficient is not an exclusive parameter for Iran and is unknown for precipitations continued for more than one day, and standard deviation is not able to introduce capabilities of a region for precipitation, assessed PMP in a statistical method is surely approximate and can not be merely relied while designing great aqua structures such as dams which are allocated a big amount of costs and credits. So it is suggested to refer to meteorological methods to calculate and control most of these parameters.

Probable maximum precipitation, Probable maximum flood, 24-hours maximum precipitation, statistical method