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Possible influences of North Atlantic Oscillation on winter reference evapotranspiration in Iran

Abstract:

The North Atlantic Oscillation (NAO) is known to be responsible for most of inter-annual atmospheric variability over the Northern Hemisphere, particularly in Europe and the Mediterranean basin. Owing to the importance of reference evapotranspiration (ET<inf>o</inf>) in irrigation planning, water resource monitoring and management, we assessed the impact of the NAO on the ET<inf>o</inf> variability during the winter months from December to March in Iran. The Penman-Monteith FAO 56 method was applied to estimate ET<inf>o</inf> based on meteorological data from 41 synoptic stations during a period of 40years (1966-2005). The correlation between the monthly NAO index and the ET<inf>o</inf> time series was computed using the Spearman's rho test for time lags from 0 to 6months. The simultaneous and lag correlation analyses demonstrated that the winter ET<inf>o</inf> series over Iran had negative correlations with the NAO index at almost all the stations. The highest negative correlation of 0.53 was observed between the January ET<inf>o</inf> series and the August NAO at Tabriz station located in the northwest of Iran, whereas the highest positive correlation of 0.55 was found between the January ET<inf>o</inf> series and the simultaneous NAO at Bandar-Lengeh station which is situated on the northern coast of the Persian Gulf. Averaged over the 41 stations, the winter ET<inf>o</inf> values during the negative phase of the NAO were about 3% higher than those during the positive phase. © 2014 Elsevier B.V.