The Study and Analysis the Clusters of Heavy Rainfall Threshold in Iarn

The aim of this study is to analyze the areas of heavy rainfall thresholds in Iran. For this purpose, daily rainfall data of over 50 years were produced from Esfezari database. In continue, percentile was used to determine the heavy precipitation threshold. In order to study and zoning the thresholds, the analysis of harmonic means has been used. By implementing cluster analysis on heavy rainfall, four zones as the following were recognized. First, the zone with great heavy rainfall threshold and coefficient of very great changes, second, zone with medium heavy rainfall threshold and coefficient of medium changes, third zone with very great heavy rainfall and coefficient of very low changes and the fourth, zone with too low heavy rainfall and coefficient of very great changes. Among the zones, the third zone, i. e. the Caspian coast has had the highest heavy rainfall threshold, while a great deal of areas in the central part of Iran has had low heavy rainfall threshold. The results of the analysis in the four zones indicate that except in the third zone, which the medium term is dominant, in other areas, the short term cycles is dominant on the Iran's heavy rain fall threshold.