Floods

The occurrence of flooding in Iran is closely related to El Nino Southern Oscillation (ENSO) events. During the warm phase of an ENSO event, the intensity and frequency of autumnal wet periods, especially for the southern districts of Iran, increase and often lead to flooding¹.

Precipitation in Iran is confined mainly to the winter season, and mostly falls in short bursts when there is little vegetation to intercept it. High intensity storms are also common in the summer months, and may trigger devastating flash floods as a consequence of the top layer of baked soil promoting rapid runoff of large volumes of water².

According to UNDP in Tehran, in the 1950s there were 195 recorded floods in the country. This number rose to 233 in the 1960s, 431 in the 1970s, 904 in the 1980s and 1,351 in the 1990s², illustrating a serious and growing problem.

¹ 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.

² Irin. 2002. Iran: Flash floods set to continue.
http://www.irinnews.org/report.asp?ReportID=29590