Investigation of scaling properties in monthly streamflow and Standardized Streamflow Index (SSI) time series in the Ebro basin (Spain)

Scaling behaviors in monthly streamflow and Standardized Streamflow Index (SSI) of 11 gauging stations in Ebro basin (Spain) were analyzed: four located in the mainstream and seven in tributaries. The time span is from 1950 to 2005. The methods used are the power spectrum and the detrended fluctuation analysis. All the streamflows are signaled by the presence of the yearly oscillation, which also plays the role of crossover between two regions: for frequencies smaller than the yearly cycle (or timescales higher than 1 year) the dynamics is approximately random, while for frequencies higher than the yearly frequency (or timescales smaller than 1 year) the dynamics is persistently correlated. The SSI shows approximately similar characteristics, although the annual oscillation is not evidenced. Except for a few peculiar features, the power spectrum and the detrended fluctuation analysis (DFA) have shown similar results for all the streamflow and SSI time series, indicating a universal scaling behavior over the Ebro basin.