The objective of the study was to investigate the El Nino forcing on the discharge of Kor River located in Maharloo-Bakhtegan basin in the Fars province of Iran. Thirty-one-year (1965–1995) and twenty-year (1975–1995) monthly mean river discharge data recorded at two stations, namely, Chamriz and Dehkadeh-Sefid, respectively, were chosen in the present study. Fourier analysis was used to extract harmonic information of time series data such as amplitude and phase angle to show the maximum effect and the time of effect of El Nino on river discharge. The study revealed that El Nino events caused increase of discharge in Kor River by 15% to 20% and the maximum influence was in the months of February and March in El Nino years. 1. Introduction In normal condition, the temperature of ocean surface in the east of southern Pacific Ocean is lower than the temperature of surface water in the west of southern Pacific Ocean. Therefore, a high pressure zone and a low pressure zone dominate in the east and the west of the southern Pacific Ocean, respectively [1]. The difference between high and low pressure zones causes wind blowing, namely, trade wind or easterlies. The direction of wind is from the east to the west of Pacific Ocean. Therefore, trade wind causes the movement of surface warm water in equatorial region from the east to the west. During El Nino period, the temperature of surface water in the west is lower than the temperature of surface water in the east of southern Pacific Ocean. This large-scale pressure seesaw in Pacific Ocean is called Southern Oscillation (SO). Therefore, the direction of trade wind and also warm water changes from the west to the east. Existing warm water pool in the coast of Peru and Southern Ecuador is the sign of El Nino [1, 2]. The two phenomena, El Nino and Southern Oscillation, together are known as ENSO. The relationship between El Nino and some parameters such as temperature, rainfall, and discharge was investigated in different parts of the world. Their results have showed that El Nino causes floods and droughts on different parts around the world [3, 4]. Cayan and Peterson [5], Kahya and Dracup [6], Zhang et al. [7], Ward et al. [8], Cahoon [9], Osman and Abdellatif [10], Mu？oz-Salinas and Castillo [11], Wang and Eltahir [12], Simpson et al. [13], Kahya, and Karab？rk, [14], and many other researchers conducted the impact of El Nino on the discharge. Cayan and Peterson [5] predicted discharge anomalies in the Western United States in two seasons by using Southern Oscillation Index (SOI). Zubair [15] investigated the
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