I have used wavelet analyses to investigate the long term (1929-2005) changes in regular patterns of monthly discharge of the River Dee, Scotland (data courtesy of SEPA Aberdeen). There were two significant patterns represented by the red patches on the wavelet power sprectrum: annual pattern due to summer low flows and winter high flows following predominant rainfall periods and six-month pattern due to spring snow melt and late summer drought. Nothing surprising, it fits what we know about the system. Yet, over the past century it is clear that these expected patterns came and went without any apparent trends.
Further work cross-wavelet analyses will try to link those patterns to underlying drivers and the method will be applied to long-term river flows in England to see how regional those changes in flow patterns may be.