Wavelet analysis of the annual discharge records of the world’s largest rivers

The determination of the temporal variability of water resources is of high importance with respect to long-term water policy. This contribution provides a wavelet-based global analysis of 55 large river discharge fluctuations located on the five continents. It shows that large river runoff records should be considered as valuable climatic proxies (such as temperature or precipitation records) since discharge series integrate intermittent 4-year and longer processes. Effectively, continuous Morlet wavelet analysis allows to identify statistically significant bands of intermittent fluctuations from interannual 5–8-year to decadal, 12–15-year, bidecadal, 28-year fluctuations and 4–70-year considering the longest time series available in Europe and North America. Reasonable physical relationships between land–water cycle oscillations and climate forcings (such as ENSO or NAO) are documented and investigated but all these results should later on be more systematically confirmed by cross-wavelet analyses.