The Analysis of Trend and Cycle Between Rainfall and Discharge in Ghaleroudkhan Basin

3 Abstract: The type and time and cycle of discharge changes in relation to rainfall in the Ghaleroudkhan basin (Iran) have been analyzed for the period '1966-2002' by applying the Man-Kendal test trend and spectral analysis. The obtained results show that time series had trend and abrupt change in monthly, seasonally and annually scale. Especially the discharge of winter, spring and summer was also seen a significant descending trend. In other words, autumn in relation to other seasons had least gradient in descending trend. In sum, with investigation to obtained diagrams, the trend of tails u of rainfall have been identical with discharge during i period which is representative of high dependence of discharge changes in relation to rainfall variable. Also, the results of spectral analysis showed that there are non sinus cycles in seasonal scale and non sinus cycles of discharge is more important and found clearer cycles for summer and autumn. The monthly rainfall and discharge cycles are weaker than seasonal cycles. Finally, in rainfall the '2-2.2', '2.7-3.8', '4.2-5.6', '7.7-9.5', '20' year sinus cycles and in discharge the '2-2.4', '2.9-3.8', '7.7-9.5' year sinus cycle are meaningful, respectively.