Trend test and change-point detection for the annual discharge series of the Yangtze River at the Yichang hydrological station

The trend test and change-point analysis have been carried out on several annual discharge series of the Yangtze River at the Yichang hydrological station, including the discharge series of the annual maximum, annual minimum and annual mean during the period 1882-2001. The results of both the Mann-Kendall and Spearman's rho trend tests show that, at the 5% significance level, the annual maximum flood series did not have any statistically significant trend, but the annual minimum flow series and the annual mean discharge series exhibited a sign of decreasing trend. For single change-point detection, a Bayesian model was established to study the abrupt change in the mean levels of the time series. Given the observed hydrological data, the Bayesian model can estimate the posterior probability distribution of each change-point location by using the Monte Carlo Markov Chain (MCMC) sampling method. The results of the Bayesian model show that, during the past 120 years, the mean levels of both the annual minimum discharge series and the annual mean discharge series have decreased by 8% and 6% respectively. Further analysis suggested that, for the annual minimum discharge series and the annual mean discharge series, both the trend term and the abrupt change term are very closely related and very hard to distinguish from each other.