Fig. 4
Local wavelet power spectra normalized by 1/σ2 (σ expressed in m3 s−1). The shaded contours are at normalized variances (m3 s−1)2. The left axis is the period (in years). The bottom axis reports the time (in years). The thick black contour encloses regions of greater than 95% confidence for a red-noise process with a lag-1 coefficient of 0.72. a The yearly averaged discharge rates from 1922 to 2021 showing the long-term periodicity of ca. 10 years from 1942 to 2002 (green circle); b the monthly averaged discharge rates from February 2000 to December 2021 showing the intermediate-term periodicities of ca. 3.5 from 2007 to 2017 (green circle; c the weekly averaged discharge rates from 2000 to 2021 showing the short-term periodicities of ca. 1 year (dotted green circle), ca. 6 months from 2011 to 2014 (green dotted circles) and ca. 3–4 months during 2001–2003 (dotted green circles). It is worth noting that 1 year periodicity is also detected in b During 2001–2003 and 2011–2014. The global wavelet power spectra are shown on the right side of each plot. The orange dotted line represents the best-fitting red-noise spectrum at the 95% confidence level