Abstract: El Nino phenomenon is a strong signal of global weather change, and it only occurs in the Equator Pacific Ocean. However, its effect exceeds far away. According analysis to historical data El Nino phenomenon has appeared 14 times in this area since 1950's, in which the one taking place in 1997 is the strongest in the 20th century. Affected by the El Nino phenomenon in1997, it happens in 1997-1998 that the climate of the areas between from the Northern Hemisphere to the Southern Hemisphere, from Africa to Latin America changed sorely. To a great extent, the floods of the Yantse River happened in 1954 and in 1998 have some relations with the El Nino phenomenon occurred in 1951-1953 and in 1997-1998. Because of the Yellow River and the Yantse River both originated from the northeast Tibetan Plateau, then what are the responses of the precipitation and runoff in the Yellow River to El Nino phenomenon? We conclude that El Nino Phenomenon should have a close relationship with the precipitation and runoff in the Yellow River basin, and El Nino Phenomenon is the main reason bringing on the runoff in the Yellow River decreasing continuously during the period from 1920 to 1930 and since 1990 based on a large of measured data. So the influence of El Nino phenomenon to the runoff in the upper Yellow River above the Tangnag Hydrometric Station and the climate features at Tibetan Plateau are analyzed and discussed. The results show that El Nino phenomenon is one of the main factors affecting runoff in the Yellow River above the Tangnag, undoubtedly. As a result, studying the responses of runoff to the El Nino phenomenon is of very important significance to long-term runoff prediction and water resources use etc for all. In the upper Yellow River if El Nino phenomenon occurs in winter of last year or in spring of this year, the probability happening the low-flow is large in the year; if El Nino phenomenon occurs in summer, the high-flow year may be happen, and the probability happening low-flow in the next year is larger. The longer the continuous period of El Nino, the lower the runoff is. If El Nino ends in spring, the probability happening dry year will be larger. If El Nino ends in summer, the high-flow year may happen in this year. If La Nina phenomenon occurs in this year, the high-flow year may happen, and perhaps the larger floods will occurs in this year or the next year.

Key words: El Nino Phenomenon, La Nina phenomenon, the Upper Yellow River, high flow or low flow