The Simultaneous Effect of ENSO and Persian Gulf SSTs on the Occurrence of the Drought and Wet Condition Over the Western and Northwestern Parts of Iran

Seasonal prediction of dry and wet spells is critical for competent management of water resources in the rain-fed wheat region in western and northwestern parts of Iran. The present study has evaluated the effects of the Persian Gulf Sea Surface Temperatures (PGSSTs) on precipitation variability of these regions during warm (El Nino) and cold (La Nina) phases of the El Nino - Southern Oscillation (ENSO) phenomenon. The results indicated that, compared to single variable, the composite effects of the PGSSTs and ENSO enhances the prediction of winter precipitation. When warm ENSO phase is coincided with below normal PGSSTs, the probability of winter drought varies from 0.50 and 0.7. This probability drops to less than 0.33 if the PGSSTs are warmer than usual. Therefore, as El Nino is approached, above and below normal PGSSTs imply less and more frequency of dry spells, respectively. The coincidence of La Nina and colder than usual PGSSTs promises the prevalence of wet condition (for winter) over most parts of the study area and a productive situation is anticipated for the rain-fed crops. On the other hand, these crops encounter a high risk of water shortage if La Nina concurs with warm PGSST epochs.