Impacts of El Nino Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) on the Olive Yield in the Mediterranean Region, Turkey

Turkey ranks the 5th in the world in terms of total olive fields, and the 4th in terms of olive production. Although this ranking varies over the years because of the periodicity feature of the olive, Turkey is an important olive producer country in Mediterranean. The olive tree (Olea europaea L.) is a member of the maquis community that is involved in the natural vegetation of the Mediterranean climate. It is accepted as a bioindicator that characterizes this zone because of its good adaptation to the Mediterranean climate. According to the report of the World Meteorological Organization (WMO), the year 2016 was determined as the year with the highest global average temperatures (1880-2018). It is considered that the variability in climatic conditions and the increasing frequency of extreme weather events (extreme precipitaion, floods, extreme temperatures, heat waves, hail, etc.) that have been occurring frequently in recent years are associated with the changes in the large-scale pressure and wind circulation and atmospheric oscillations (with direct and indirect effects, e.g. NAO-North Atlantic Oscillation, AO-Arctic Oscillation and ENSO-El Nino Southern Oscillation, etc.). In this study, the effects of Southern Oscillation (El Nino/ La Nina) and North Atlantic Oscillation (NAO) on the olive yield in Turkey will be examined. The objective of this study is to a.) determining the statistical relationship between climatic conditions and atmospheric index values during the phenological periods of olives, b) determining the effects of oscillations on yield by examining the years of strong atmospheric oscillation indexes and yield values on the line graph. To do this, the phenological periods of the olive were determined. Daily average temperature data of 48 years covering the years 1970-2017 for Adana, Osmaniye, Kahramanmaraş, Antalya, Mersin and Iskenderun meteorological stations, and daily average total rainfall data were used as the climatic data. Nino 3, Nino 3.4, Nino 4 and ONI indexes representing the El Nino activities and effective during the 1970-2017 period and the NAOI index representing the North Atlantic Oscillation were used. The relationship between the monthly average temperatures which were effective in the phenological period of olive and the atmospheric index values was statistically analyzed according to Pearson correlation coefficient method. As a result of the analyses, statistically significant relationships varying between 40-64% were found between average temperatures during the flowering and first initiation of fruit period among the phenological periods of the olive and Nino 3.4 and Nino 3 indexes. Statistically significant relationships varying between 38-60% were found between total rainfall and Nino indexes. In addition, no statistically significant relationship was found between North Atlantic Oscillation Index (NAOI) and climatic conditions. In order to determine the effect of the oscillations on yield by determining the yield values on the line graph with the years with strong atmospheric oscillation indexes, yield values of the olive covering the years between 1991-2017 were used. According to this, the yield of olive was below the average in the strong El Nino years, which were determined as 1991, 1997, 2009, 2015 and 2016. These years in general correspond to the periods when drought was experienced in the area including the Mediterranean Region in Turkey.