Hidrológiai Közlöny 1990 (70. évfolyam)
6. szám - Haidu Ionel–Tilinca Zeno–Szőcs Francisc: A lefolyás vízhozamainak idősor-elemzése Románia nyugati részének folyóin
HAIíDU I. et al.: A lefolyás Idősor-elemzése 333 Spectral Analysis of the Multiannual Flow Variations of the Rivers in the West of Románia Hairtu, I., ITilinca, z f, Szőcs, F Abstract Thepresent paper inaimed at the causal decomposition of the spectruin of the multiannual flow variation and the isolation of the components of the dynamic series shown in the relation (1). The data utilized refer to the average annual diseliarge of the rivers in the West of Romania and inside the Carpathian arc, recorded during the period 1950—1984 in more than forty hydrometrie stations (Fig. 1). Wehadinviewthe determination of the generál trend (Fig. 2), of the optimál periods and amplitudes of the cyclic components, (figs. 4 and 5) outlining the final cyclic component and the aleatory component (Fig. 6). A working method is employed which performs the spectral analysis of a dynamic series through the following stages: the determination of the generál trend by a polynomial adjustment (relation 2), the flattening of the fluctuations using the shifting average, the identification of the optimál periods by means of the autocorrelation coefficient (relation 4, fig. 3) and by means of the spectral intensity (relation 5, fig 3), the representation of the partial cyclic components (fig. 4, 5) and of the final cyclic component (fig. 6) by a Fourier series (relation 6). The final cyclic component results from the addition of the cyclic components specific to the optimál periods determined. For the multiannual flow variation in the west of Romania, periodicities of 11—12 years and of approximately 5 years are identified (table 1), and the existence of periodicities about 2—3 years is supposed. Bystudying the variation of a dinamic series during oneyear, somé periodicities of less than one year will be pointed out, representing the mode of manifestation of the seasonal factors. In the case of the multiannual variation, the factors which induce the variation of the phenomenon during the year counterbalance reciprocally, therefore the series of the annual average values will contain only those factors which determine the variation of the phenomenon from one year to another. Weconsider that the systematic component of the flow (u(í)-fv(í)) is brought about by certain generál factors of atmospheric circulation, whereas the aleatory component e(í) results from the totalized experisson of the local physical-geographical conditions of the hydrographic basin in the situation of variability of the atmospheric circulation from one year to another. Another scope of the paper refers to the identification of the influences exerted by the size, average altitude and geographic position of the basin relatíve to the particularities of the atmospheric circulation, upon the multiannual flow variation. The paper f urther presents critical considerations regarding the procedure for the decomposition of a limited multiannual dynamic series exhibiting substantial variations from one year to the other. Beyondtheoreticalresults,the methodology utilised provides, from a practical point of view, the possibility for the elaboration of prognoses. Koywords: spectral, flow, multiannual, Fourier, periodicity, prognose.
