Variation in frequency and proportion of duration of rainy days in Iran’s precipitation

In any given region, climate change can be manifested in the form of various characteristics of climatic elements. In the present study, the frequency of different duration of rainy days was examined to investigate the precipitation variations as a sign of climate change. To this end, gridded precipitation data were used from 1971 through 2016, and days with more than 1 mm of precipitation were considered rainy days. According to the rainy days’ frequency, it was revealed that during the study period, 1 to 36 days of duration occurred in the country. The 1-day duration had the highest frequencies and covered the vastest areas, while 36-day duration had the lowest frequencies and covered the minor areas. Accordingly, the 1-day duration played the most significant role in annual precipitation. The proportion of these rainfall events in some country’s dry and semi-dry parts was more than 80%. The findings also revealed an increased frequency of short-term, especially 2-day duration, in large parts of the country and a decrease in the long-term duration. The results showed that latitude and longitude had the most significant impact on the frequency distribution of the duration of rainy days. Latitude had a direct effect (excluding the 1-day duration of annual precipitation), and longitude had an inverse effect (except the 1-day duration of annual precipitation) on the precipitation duration.