Drought
Iran suffers from droughts with a typical return period of every one to three years1. The occurrence of drought in Iran correlates closely with El Nino Southern Oscillation (ENSO) events in the Pacific. When a vigorous La Nina event prevails the chance of dry conditions occurring are high and the probability of a severe autumn drought is intensified. In contrast, during winters of warm ENSO phases, the north-western and south-eastern districts of Iran tend to suffer from drought2.
1 Abbaspour, M & Sabetraftar, A. 2005. Review of cycles and indices of drought and their effect on water resources, ecological, biological, agricultural, social and economic issues in Iran. International Journal of Environmental Studies. Vol. 62, pp 709-724
2 Nazemosadat, M.J & Ghasemi, A.R. 2004. Quantifying the ENSO-related shifts in the intensity and probability of drought and wet periods in Iran. American Meteorological Society.