HIDDEN HARMONIC FLUCTUATIONS OF ANNUAL RIVER FLOW: THE POSSIBILITY AND EXPEDIENCY OF IDENTIFICATION AND ASSESSMENT

Abstract

The article shows the possibility and necessity of revealing hidden harmonic fluctuations of long-term runoff throughthe example of two rivers in Eastern Siberia.Identification of the harmonic component in the series of annual river flow is necessary for a number of reasons:– to determine the potential statistical predictability of the series;– for a correct assessment of the main trend of the long-term flow dynamics;– to reduce the limits of uncertainty during the assessment of future changes in annual runoff in the absence of long-termforecasting techniques.Finally, the accumulation and generalization of data on the patterns of long-term fluctuations in runoff over the entire surfaceof the Earth is, probably, one of the ways to identify global patterns and the development of hydrometeorological phenomena in general.In the case under consideration, the presence of a harmonic component was revealed grapho-analytically, including by meansof visual analysis of graphs of long-term fluctuations, followed by selection of an analytical expression of the function. Then the qualityof approximation by harmonic and linear functions, as well as by the norm, was compared, which showed the advantage of the former. Along with the grapho-analytic method, the calculation procedures of the autocorrelation function and spectral analysis wereapplied to the calculation series. In both cases considered in the article, these calculations confirmed the presence of a harmonic component with similar periodicity values.It is concluded that the applied methods, despite the limitations and disadvantages characteristic of each method, taken together,make it possible to identify annual runoff series with a pronounced harmonic component.