Exploration on statistical methods for analyzing correlations between rainfall and sediment discharge in base period by hydrologic method in the Xinshui River Basin, Shanxi Province of northern China

  Objective  This paper analyzes the trend and relationship between rainfall and sediment discharge in the Xinshui River Basin in Shanxi Province of northern China from 1958 to 2015 based on the daily rainfall and sediment discharge data, aiming to select the best statistical method according to the effects of rainfall spatial distribution and six statistical criteria of rainfall on calculating the relationship between rainfall and sediment discharge used for the “hydrologic method” in base period. The six statistical criteria of rainfall included the annual rainfall, the flood season rainfall, the erosion rainfall, the mild sand-producing rainfall, the moderate sand-producing rainfall and the heavy sand-producing rainfall.

  Method  Mann-Kendall method was selected to analyze the trend of rainfall and sediment discharge, double mass curve was applied to determine the base period of “hydrologic method”, and Pearson correlation analysis was used to compare the results of correlation between rainfall and sediment discharge.

  Result  There was no significant changing trend of annual rainfall in Xinshui River Basin, but the annual sediment yield showed a significant decreasing trend. The Pearson correlation coefficients between rainfall and sediment yield under the six statistical standards were ordered from high to low as follows: the heavy sand-producing rainfall, annual rainfall, the erosion rainfall, the moderate sand-producing rainfall, the mild sand-producing rainfall and flood season rainfall. The contribution of rainfall with low intensity but high amount on sediment was small. The correlation coefficient between rainfall and sediment yield can be enhanced by eliminating the invalid rainfall for sediment. The correlation coefficients between rainfall and sediment discharge of Wucheng, Huangtu, and Puxian rainfall stations were higher, and the results of Daning, Sang’e rainfall stations were lower.

  Conclusion  The change of annual sediment yield is directly related to the human activities such as the Three North Protection Forest Project and the construction of check dams. Sediment discharge is mainly caused by heavy rainstorm in summer and autumn. The heavy sand-producing rainfall can be used to analyze the relationship between rainfall and sediment discharge, and the flood season rainfall is not suitable for the analysis of the relationship between rainfall and sediment discharge. Invalid rainfall for sediment will increase the deviation of the correlation coefficient between rainfall and sediment discharge. Rainfall with short time duration and high amount should be selected to analyze the correlation coefficient between rainfall and sediment discharge when rainfall intensity data are scarce. The relationship between rainfall and sediment discharge is influenced by the spatial distribution of rainfall stations at the watershed scale.