Investigating the trend pattern analysis of the monthly heavy rainfall threshold happening in Iran during the last half century

This study aims at analyzing the temporal and spatial changes of the happening of monthly heavy rainfall threshold in Iran. To do so, daily rainfall data from Asfrazydatabase provided by Dr. Masoudian in Isfahan University, were applied. These dada are from the beginning of the establishment year up to 1383. In order to complete the data from 1383 to 1390, the daily rainfall data for 459 stations were extracted from meteorology organization and by using the same method and the interpolated technique were added to the database of priMarchy data. To perform calculations and to do graph processes, the programming facilities in software environment of Matlab and Surfer software were respectively applied. To analyze the trend pattern, Moran spatial index was used. The findings showed that the variability coefficient of monthly heavy rainfall threshold is very high in Iran, such that the most variable coefficient of monthly heavy rainfall threshold has been happened in the warm months of the year in south and south east of the country, and due to the entrance of rainfall mass to Iran in cold months, it has been happened in the south and south west. Nevertheless, in warm months of the year, southeast areas of the country enjoy high threshold due to the influence of seasonal rainfall. So, it can be mentioned that the increase or decrease of heavy rainfall threshold, in addition to being influence by local factors is extremely influenced by measure macro factors and external factors. The results of trend pattern analysis of thresholds indicate that the spatial self-correlated pattern in cold months enjoy a low cluster pattern and decreasing trend. The positive spatial self-correlated pattern in the warm months and cold months of the year are respectively in decreasing and increasing trend.

Keywords:

thresholds , variability coefficient , trend , Moran index , Iran