Probabilistic occurrence of the average autumn rainfall in Iran related to ENSO events

The average rainfall is considered as an essential threshold for the evaluation of climatological condition in a particular year. The influence of the El Niño-Southern Oscillation (ENSO) phenomenon on the probabilistic occurrence of average rainfall (POAR) was explored for the period 1951–1995. The study has been carried out for autumnal rainfall in both seasonal and monthly time-scales. It was found the POARs have increased (decreased) during warm (cold) episodes for the most parts of Iran. However, for the eastern parts of the Caspian Sea coasts, warm (cold) incidents induce a significant decline (improvement) in POAR values. Successful seed germination, early growth of crops, less autumnal air pollution, more than usual water storage in dam reservoirs and increase in soil water content are expected during intense warm episodes.