Effect of ENSO phenomenon on irrigated and rain-fed grape yield of Iran

The yield of agricultural crops is one parameter closely correlated to weather features. The ENSO phenomenon is a climate parameter that affects weather, climate and agricultural production. Iran is one of the top producers of grapes in the world. With the large area of cultivation and high grape production, this product can be exported. In addition to grape yield importance, the effects of ENSO on agriculture that has been confirmed by researchers, and the lack of similar studies on the grape plant especially in Iran, the purpose of this investigation is to evaluate the effects of ENSO in El Nino and La Nina phases on grape yield.
In this study, for evaluation of the effect of ENSO phenomenon on grape yield, irrigated and rain-fed grape cluster weight information as a yield of 27 different provinces during 1999 to 2015 was used. For assessment, the effect of ENSO, the information of nine different indices of ENSO including SOI¡ PNA¡ NOI¡ NINO 3.4¡ NINO 1¡ NINO 3¡ NINO 4¡ MEI and TNI were provided. Pearson correlation coefficient was used for the determined relation between ENSO indexes and yield amount in SPSS software. Finally, the zoning maps with considering irrigated and rain-fed grape yield in El Nino and La Nina phases were drowned.
The results showed that NINO 1 index in April was the most effective of the ENSO indices on irrigated grape yield and PNA index in August had the highest correlation with rain-fed grape yield. Comparing the correlation between ENSO and grape yield indicated that the effect of ENSO on irrigated grape yield was more than the rain-fed yield (.633 against -0.534). The comparison of average grape yield in each of El Nino and La Nina phases showed that La Nina phase led to an increase of 24.5% in irrigated grape yield. The average yield for irrigated grape in La Nina was 11,822 kg/ha, and in El Nino was 9,490 kg/ha. While the average rain-fed grape yield during La Nina was 2,401 kg/ha, and during El Nino was 3,552 kg/ha, which indicated increasing rain-fed grape yield during El Nino to La Nina with a value of 47.9%. These results were in line with the studies of Zareabyaneh and Bayatvarkeshi (2012), Yousefi and Hajjam (2012), Khorshiddoust and Ghavidel Rahimi (2006) and Moron and Plaut (2003).
In total, the effects of the ENSO phenomenon on irrigated and rain-fed grape yield in the country was confirmed. The effect of ENSO on agriculture productions, however, depends on the type of plant, kind of cultivation and study area. It can be expected that the results of the ENSO effect on each agricultural plant are not generalized. Moreover, further study of each crop in each region is needed.