Variations of Daily Danube Discharge at 16 Gauging Stations

Abstract

AbstractThe river discharge is the main source of freshwater for large surface areas. Its deep minima are connected with drought events, while its maxima – with floods. The time series of river discharge consist of significant seasonal variations, modulated by long-term oscillations. The seasonal, interannual and decadal cycles of Danube river discharge are studied by time series of mean daily data from 16 stations. The data from Orsova station started in 1840. Three stations started in 1900, and the rest – in 20s of the last century. Time series of maximal discharge and seasonal amplitude are created. Their variations in narrow frequency bands are analyzed by the Method of Partial Fourier Approximation (PFA) and compared with the corresponding cycles of the solar activity. The amplitudes of seasonal harmonics from the PFA are compared for all stations. The time delay of the 11-year solar signals to the reaction of river discharge at used stations, is determined from the phase differences. The solar influence on maximal Danube daily discharge is manifested by synchronous 10.6-year cycles of station discharge and sunspot numbers, where the river reactions are delayed to the solar signals in the frame of 0–3 years. New models of river discharge, based on solar cycles and lunar tides, are proposed. Possible forecast of periods with maximal river discharge is discussed.KeywordsRiver dischargeSeasonal variationsSolar cycles