The study of daily precipitation probabilities and distribution in Hamedan meteorological station

In Iran some crops are often grown using irrigation to supplement the rainfall. Therefore, in order to achieve good cultivation we studied the water requirement of crops for a week. It is not known how much rain would fall during the week, or the beginning of each week. Therefore, precipitation records could be examined to estimate the amount of expected water. Some studies using a simple model suggest that the amount to allow for cultivation should be 30% of point distribution of total precipitation for that week. Hence, this study considered that there was 30% of total rainfall for each week. The data available were daily records for 45 years (1961-2005) in Hamedan meteorology station. Weekly total precipitation was calculated. Two different methods of estimating 30% of data through the year were considered. The first method merely involves calculating the observed 30% of data and then, 'smoothing' the original estimates and fitting gamma distributions. Results show that in this station there is two precipitation periods (in 1-21 weeks and 45-52 weeks) and have one dry period (22-44 week).