Determination of time probability distribution pattern of storm rainfall in Sistan & Baluchestan Province (Iran)

The first step in many commonly used methods for estimation of design floods is choice of a design rainfall. Design rain has some characteristics such as time distribution of rainfall in rain period. In this research, the data of nine rain gauge stations in Sistan & Baluchestan province has been used. In this method, in every time duration based on this fact that in which quarter the maximum rain has happened the first, second, third and fourth rainstorms were defined and the related charts with 10 to 90% probability were prepared. The results show that: the maximum abundance of rainstorms in short-term duration is related to first quarter rainstorms and in all stations except Khash, Kahir and Sarbaz stations the 1, 2, 3 and 6 hours durations are the main first quarter rainstorms. In 9, 12, and 18 durations the rainstorms in each four quarters is distributed and in 24 hours duration except Kahir station, the others are in second quarter rainstorms. In Sistan and Baluchestan province about 80% of rain happens in short-term durations, in first and second rain quarter and in long-term durations it happens in third quarter.