Determination of Dominant Periods in Rainfall and Runoff Time Series (Case Study: Ardabil Plain)

This study analyses the trends in runoff and rainfall data at monthly timescales observed at three rainfall and one runoff stations of Ardabil plain in 1350-1394 period. The purpose of this study is to analyse the trends in runoff and rainfall time series using MK1, MK2 and MK3 tests. Also, in order to determine the dominant periodic components applied hybrid Wavelet Transform and MK1 test. The results of MK1, MK2 and MK3 tests showed that decreasing trend is prevalent in rainfall (P1) and runoff (R1) of Samian station and positive trend in rainfall of Gilandeh (P2) and Kozatopraghi (P3) stations. Also, rainfall time series have not shown non-significant trend. But runoff time series were shown significant trend. The results of MK after removing the effect of all significant serial correlation (MK3) showed the value of trends decreased in comparison to MK1 parameters. Generally, short-term periods were important in the involved trend at original time series. Thus, the rainfall data showed short-term periods of 2 months (A+D1) in monthly scales, respectively. In the runoff time series, wavelet-based detail at level 3 plus the approximation (A+D3) time series was conceded as the dominant periodic component.