Improvement in Intensity-Duration-Frequency Relationships of Rainfall in Iran

Rainfall intensity with different frequencies is needed for many hydrologic models. Rainfall intensity–duration–frequency relationships (IDF) have been investigated for different regions using previously recorded data. Iran Meteorological Organization has prepared IDF curves for 66 stations in Iran since which are the most updated data. Comprehensive IDF relationships were developed for these data. The results showed remarkable changes when compared with previous studies of Iran. This may be due to a change in parameters of probability distribution function as a result of increased record length of stations. Some relationships were also developed for ten year-hourly ( P6010) rainfall estimation from some parameters such as average annual rainfall and average maximum daily rainfall. Such a relationship was made for all stations and also for different classifications of regions (based on average annual rainfall and apparent climatically divisions). The validity of all relations was analyzed for eight independent stations with suitable spatial distribution. It was shown that all relationships are nearly valid as far as a suitable region is choosen. The previous relationship for Iran is not useful at present.