The Effect of Madden - Julian Oscillation (MJO) on the Variation of Reference Evapotranspirationin Southern Regions of Iran

Frequent anomalies on air pressure and atmospheric circulation patterns sometimes impose their impacts on a location far from its starting point. This kind of atmospheric disturbance is known as andraquo;Teleconnectionandlaquo;. Madden-Julian Oscillation is a teleconnection pattern and dominant form of tropical and sub-tropical intra-seasonal variations that plays an important role in atmosphere-ocean cycle system. Since, climate change causes changes in meteorological parameters; therefore, reference evapotranspiration and in general, crop water requirement might change accordingly. Having considered the issue of water scarcity in Iran and importance of evapotranspiration irrigation management, the impact of different MJO phases on reference evapotranspiration in several southern sites of Iran (during 1979 to 2008) was evaluated by different statistical methods in this study. The daily ET0 values were estimated by REF-ET software and Penman -Monteith FAO-56 method. The MJO data, according to Wheeler and Hendon (WH) definition, were obtained from National Oceanic and Atmospheric Administration (NOAA) database. The ET0 and MJO statistical pairs, in different phases and months were sorted for each study sites accordingly. Using Pearson and Spearman correlation methods, linear regression and selection of forward method, the impact of MJO signal on ET0 for each month and all WH phases was extracted. Results indicated the significant effect of MJO signal on ET0 values for the study stations. The maximum number of correlations was observed for Bandar-e-Lenge station. In addition, the larger effects were obtained for phases close to southern coasts of Iran. In this regard, the phases 1 and 8 showed the highest significant correlation coefficients and largest mean andbeta; values. It was found that the all-site average of correlation coefficients between the statistical pairs of MJO- ET0 is 0.26. During the course of the year, the highest and lowest significant impact of MJO on ET0 was occurred in July and March respectively.