Investigation of the Effect of ENSO Hot Phase on the Instantaneous Floods in Two Climates of IRAN

Considering the casualties and economic damage of flood, the study and analysis of this phenomenon is of great importance. Many studies demonstrated the effect of climate signals on the intensity, duration and timing of meteorological variables. In this paper the effects of positive phase (El Niño) of the South fluctuations of Pacific Ocean on the occurrence of floods in the Gorgan-Rood Gharesu basin (as a Wet and Mediterranean Climate) and also Tashk Bakhtegan Maharloo (as a Dry and Semiarid Climate) are investigated, using the Oceanic Niño (ONI) index. For this purpose, the “extreme value distributions of the Gumbel” and the “Time Variation Analysis” in two phases “neutral” and “the occurrence of El Niño” were employed. Results of Gumbel distribution and Maximum instantaneous discharge showed that there are influences of El Niño with 23 and 8 events in the Gorganrud-Gharesu basin and the Tashk-Bakhtegan-Maharlo basin, respectively. The results also showed that the effect of El Niño on time variation in the Gorganrud-Gharesu basin is greater than of Tashk-Bakhtegan-Maharlo basin. Moreover, the ONI positive phase in the maximum instantaneous flood of the Gorganrud-Gharesu basin is more effective than the Tashk-Bakhtegan-Maharlo Basin.