Spatiotemporal variation and cause analysis of rainfall erosivity in the Yangtze River Basin of China

The Yangtze River Basin has been the largest area of soil and water loss in China. The precipitation can induce rainfall erosivity, and soil erosion. It is necessary to determine the trend and major causes of annual rainfall erosivity in this area. In this study, a linear regression and Mann-Kendall significance test were applied to analyze the long-term trend of annual rainfall erosivity, erosive rainfall, rainy days, and rainfall intensity in the Yangtze River Basin and the 12 secondary water resources divisions. The daily precipitation data was collected to be homogenized during 1961-2017. A Spearman's rank partial correlation analysis was conducted to determine the major factors that caused the trend of annual rainfall erosivity, in terms of the erosive rainfall, rainy days and rainfall intensity. General Extreme Value (GEV) distribution function and revision coefficient were used to analyze the erosivity in the rainfall event under the 10-year return period. The difference in the two periods of 1961-1990 and 1961-2017 was used to reflect the possible impact of the extreme rainfall on soil water erosion. The climatic risk of soil water erosion was also addressed comprehensively from the perspective of the overall trend and extreme changes of annual rainfall erosivity. The results showed that: 1) There was an increasing trend in the annual rainfall erosivity, erosive rainfall, rainy days, and rainfall intensity during 1961and 2017, indicating the significant trend of rainfall intensity. The spatial distribution of trends was quite different among the four elements. The mean annual rainfall erosivity was larger than the normal during the 1990s and 2011-2017 period, indicating a peak value during 2011-2017. 2) There was an increasing trend in the annual rainfall erosivity of the most secondary water resources divisions, particularly on the three divisons of Dongting Lake Basin, the main stream below the Huko, and Taihu Lake Basin. Only Minjiang and Tuojiang Rivers Basin showed a significant decreasing trend. It infers that there was a different changing trend of rainfall erosivity in each division. The increasing trend of annual rainfall erosivity in most divisions was attributed to increasing the trend of erosive rainfall and rainfall intensity. Specifically, there was a leading role of intensity as a result of the significant increasing trend in many divisions. The annual erosive rainy days were one of the main influencing factors in individual districts, indicating a less effect than the other two factors. The significant decreasing trend of the Minjiang and Tuojiang Rivers was caused by a similar trend of erosive rainfall and intensity. 3) There were 71.6% stations with an increasing trend of annual rainfall erosivity. The increasing ratio of erosivity rainfall event was 61.2% in the 10-year return period between the two periods of 1961-2017 and 1961-1990 to the total stations. 4) One or both of the above two conditions can bring about the climatic risk of soil water erosion. Generally, the increasing climatic risk areas of soil water erosion were widely distributed, where the proportion of stations reached 81.5%. Particularly, the proportion was 51.1% under both increasing conditions, which was very unfavorable to the prevention and control of soil water loss. This finding can provide a strong reference for eco-environmental protection, sustainable development, targeted and refined water, soil protection, and watershed management in modern agriculture. © 2022, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.