We have analyzed the statistical characteristics of riverflow variability in the Odra River basin in southwestern Poland. In particular, we have examined the daily discharge time series recorded at 15 sites from November 1971 to October 2006. The skewness and kurtosis values of the time series are computed to determine if the empirical distribution of the data follows a normal distribution. The empirical distributions of all the time series are found to be non-Gaussian. The kurtosis values are interpreted in terms of intermittency, and together with skewness they are found to be significantly correlated with morphometric properties of the subbasins. In addition, several theoretical probability distributions are fitted to the riverflow data at each site. Among them, the 5-parameter Wakeby distribution is found to provide the best overall fit. Subsequently, the Wakeby distribution is used to calculate the return periods. Finally, the trend and stationarity around a trend of the various riverflow time series are assessed using the Cox-Stuart and Phillips-Perron (Dickey-Fuller) statistical tests. A decreasing trend is found in the daily discharge data at all sites, but there is no evidence of nonstationarity around the trend over the time span of the data record. A good understanding of the statistical characteristics of riverflow fluctuations in the Odra River basin is essential for water resources planning and management, including flood control and prediction in SW Poland.
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