Analysis of the change frequency distribution of daily precipitation APHRODITE database in Iran

Analysis changes in characteristics of daily precipitation is important in water resources planning and planting patterns. In this research، the changes most fitting frequency distribution and its parameters over time were examined. For this purpose، we used daily precipitation data gridded precipitation APHRODITE database 0. 2 *0. 25 degree longitude/ latitude in the Middle East. Daily precipitation data from this database within time interval of 22. 03. 1951 –20. 03. 2007 (equals 20453 days) was extracted with Grads software. To track changes over time، the data was divided into two periods of 28 years. First period from 22. 03. 1951 to 20. 03. 1979 Precipitation data were inserted in an array with dimensions of 10226*2491 and the second period from 21. 03. 1979 to 20. 03. 2007data in an array with dimensions of 10227*2491 (days on rows and pixels on columns). For fitting the frequency distribution the Kolmogorov-Smirnov test were applied. With Scripting by Matlab software were fitted distribution functions in normal and gamma type of each pixel with precipitation. Only gamma and exponential distributions were statistically able to obtain the conditions required for the test as the most suitably fitted distribution in Level of confidence 95%. Changes in the spatial and temporal frequency distribution precipitation it is not confirmed as one of the components of climate change tracking. The most fitting indicates calculated using linear momentum distribution indicates slight changes in the spatial distribution pattern of these parameters. But this change does not follow a specific pattern. The standard deviation indicates the parameter mapping in most area of central Iran and the West in recent decades has reduced confidence in the precipitation.