Evaluating the Non-Stationary Characteristics of Annual Streamflow in China for the Period 1960–2000

Abstract:

We analyzed key features of annual flows (mean, variability and skewness) and their changes during the past 50 years at 510 hydrological observation stations in China. Regional statistical features of annual flows were explored by empirical relationships between hydrologic characteristics and relevant independent parameters, e.g. mean annual flow vs. standard deviation of annual flows, coefficient of variation of annual flows vs. catchment area, and mean annual flow vs. catchment area. Changes of the statistical features were analyzed by comparison of these features before and after change points of the annual flow series, which were identified using a statistical method and the relationship between the annual streamflow and precipitation. The results indicate that: 1) the relationship between the statistical features and the relevant independent parameters shows the separation of the two curves, representing north China (arid and semi-arid regions) and south China (humid regions). 2) The annual flows and their statistical features were changed significantly at nearly 70% of the observation stations during the period 1960–2000. The annual mean streamflow decreases in north China; however, the increasing trends occur in south and southwest China. 3) The annual streamflow over most areas of China is fed by precipitation, however, the decline in streamflow is faster than the decreases of precipitation since 1970s in arid and semi-arid of north China. Thus the annual streamflow presents a non-stationary change over time and space due to the precipitation variations and the strong influence of human activities.