investigation of proportion of Daily Maximum precipitation to Annual precipitation in Iran

The proportion of daily precipitation to the annual precipitation (PDPAP) is a criterion to recognize the intensity of daily precipitation. The high proportion demonstrates that it is possible for the annual precipitation to occur only in a few days. The high proportion reveals that having heavy and showery precipitation is normal. In contrast, the low proportion shows that there are moderate precipitation and more precipitation days. In the present research, data of the highest amount of daily precipitation of 46 Iranian synoptic stations from 1976 to 2005 were collected from the country meteorology organization to measure the proportion of daily maximum precipitation to annual precipitation. In the first, statistical methods including correlation tests, simple and multiple regressions, analysis of variance and the Friedman, nonparametric tests were used to measure the impact of independent factors of height, geographical longitude and latitude on that proportion and to judge the significance of the proportion changes of daily maximum precipitation to annual precipitation during the statistical period as well. Then, charts and maps were used for visual assessing and finally by using the Ward, s clustering method, the continental survey of the stations under study was presented based on the proportion of precipitation. Measuring the impact of geographical latitude on the proportion of daily maximum precipitation to annual precipitation of Iran showed that the proportion is increasing with latitude declining. Evaluating changes of the proportion of daily maximum precipitation to annual precipitation during the statistical period in the stations showed that those changes were significant only in the case of the Sanandaj station. Those changes of the proportion throughout Iran (46 station) made it clear that the first decade did not have any significant relationship with the second one, but changes in the third decade had increased in a significant way in comparison with the first one. The results also manifested that there was a significant relationship between the maximum amount of daily precipitation of the stations and their annual precipitation. Eventually, the continental survey of the stations illustrated 5 continental classes based on the proportion of daily maximum precipitation to annual precipitation in Iran.