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The Madden-Julian Oscillation (MJO) and El Niño Southern Oscillation (ENSO) are known as the primary modes of large-scale climate variability in the equatorial parts of the Indian and Pacific Oceans, respectively. The present study has made an effort to analyze interactions of these two oscillations during boreal autumn and the feedback of these interactions on the occurrence of dry or wet periods in Fars province. Cold and warm phases of ENSO (La Niña and El Niño, respectively) are then classified according to the size of the SOI. Then positive and negative phases of the MJO were defined according to the algebraic sign of the real-time multivariate MJO series 1 (RMM1). Daily values of October-December precipitation data of 9 synoptic stations of Fars province were obtained for the 1974-2013 period. Precipitation amount and the occurrence probability of precipitation were investigated for La Niña, El Niño MJO positive phase, MJO negative phase and other four combinations of these phases. Since the impacts of ENSO or MJO phases on precipitation variability had been studied previously, the present study mainly motivated to investigate precipitation characteristics for the episodes that El Nino or La Nina events were concurrent with the MJO positive phase (El-P or La-P, respectively) or MJO negative phase (El-N and La-N, respectively). The characteristics of atmospheric circulation and vapor transport over the ocean waters and the Middle East are then investigated to justify the obtained results. Some parameters including precipitation, intensity and occurrence probability of a rainy day were computed for all phases, separately. The ratio between these parameters during opposite phases was computed and spatially mapped to evaluate the effects of the interactions. The results indicated that the frequency of the positive and negative MJO phases is significantly associated with the ENSO condition. Differences between the frequency of the positive and negative MJO phases during the El Niño events were found to be insignificant. Contrariwise, during the El Niño events, the frequency and occurrence probability of the positive MJO phase are about twice than corresponding statistics during the MJO negative phase. It was found that ENSO and MJO have a significant influence on autumnal precipitation in Fars province. During El Niño or negative MJO phase, the mean occurrence probability and intensity of precipitation were significantly greater than the corresponding values during La Nina or positive MJO in Fars. For almost entire parts and for the periods of El Nino, precipitation has significantly enhanced or suppressed during the negative and positive MJO phase, respectively. On the other hand, such differences are not significant when the opposite phases of the MJO have concurred with the La Nina events. Compare to El-P, mean precipitation during El-N has increased by about 300% in the southeast and about 70% in the eastern districts. When the El-N phase has prevailed, the autumnal precipitation intensity has increased about 40-110% and 4-40% over the southern and northern area of Fars, respectively. [ABSTRACT FROM AUTHOR]

Flood forecasting and the study of the factors involved in flood events form important issues of concern in water resources management. In recent years, the influence of large-scale global climate phenomena on flood peaks has attracted more attention. In this paper, the effect of El Nino-Southern Oscillation (ENSO) is investigated on annual maximum flood (AMF) in Iran’s southwestern basins. The basins are located upstream of Dez and Karun-I dams. ENSO effects on probability, magnitude, and intensity (probability times magnitude) of AMF in the Esfand-Farvardin (March-April) period are examined. The results indicate that following El Nino, the probability of an AMF occurrence larger than the AMF corresponding to neutral ENSO conditions is higher in the study period. The opposite is true for La Nina conditions. It is also seen that El Nino effects are more intense than those of La Nina period.