Estimation of Maximum Possible 24-Hour Precipitation Using Local spatial Variations in Southern Kohgiluyeh-e-Boyerahmad Watersheds

To design water constructs, such as spillways, canals and many other water structures one needs to estimate probable maximum precipitation (PMP). Since climate variability and spatial variations affect PMP estimation selection of proper statistical method, which provides better estimation is important. Based on general frequency equation, Hirschfield method has been proposed for this purpose, but it overestimation makes it unfavourable. Therefore, the aim of this research is to estimate PMP24 of Kohgiluyeh-e-Boyerahmad region using frequency factor. The PMP trend was calculated using long term meteorological data. Data of 3 out of 31 stations showed trends, which were omitted from further processing The simulated statistics of the 28 selected stations shows that the 3-factor log-normal is the best model to fit the data. The homogeneity factor (H1) is -1.61, which shows a slight non-homogeneity in the region. Therefore, the biggest frequency coefficient could be used to estimate PMP24 in all stations, which were 4.45. Using these criteria the calculated PMP of all stations were used to draw isohyet and reveal special rainfall distribution.