Long term variability of the Danube River flow and its relation to precipitation and air temperature

- Monthly series from the Danube River are analysed by wavelet analysis and coherence.
- Discharge, precipitation, air temperature time series are examined.
- Long cycles are present in discharge and precipitation time series.
- No significant long cycles are present in the air temperature time series.
- Precipitation and discharge spectra are correlated in low frequency intervals.

SummaryIn this work the long cycles and long range dependence of monthly discharge, precipitation and air temperature time series from the Danube River during the years 1901-2006 were analysed using wavelet analysis, with emphasis on wavelet coherence and cross wavelet spectra. All time series were deseasonalized prior to the analysis. Long cycles with 11-15 year periods during almost the whole observed period in discharge and during 1935-1975 in precipitation were found. Furthermore a reappearing four year cycle was found in all discharge time series. No significant long cycles were found in the temperature time series, which on the other hand display long term persistence. The cross-wavelet spectra and the wavelet coherence show strong correlation between the precipitation and discharge spectra in the low frequency intervals. Furthermore, a convolution of precipitation and catchment response function was used to examine the propagation of long cycles from precipitation to discharge. The results show, that the long range dependence in precipitation propagates into discharge and that the precipitation lead in the cross-wavelet spectrum increases with the increasing response time. The results indicate that especially mean monthly precipitation could be used as input variable in order to improve stochastic discharge modelling.