Abstract: Rainfall erosivity is an important index used to characterize the intensity of rainfall erosion, which is of great significance to the research on potential risk of soil erosion in the study area and for model predictions. To analyze the spatiotemporal variation trend of rainfall erosivity in the Nandu River Basin, based on the daily rainfall erosivity model, daily rainfall data recorded at 13 meteorological stations in the basin and its surrounding areas from 1971 to 2020 were used to systematically study the rainfall erosivity at different spatiotemporal scales. The research methods included the application of the Mann-Kendall nonparametric trend/mutation test, wavelet analysis, and inverse distance weighted interpolation to determine the spatiotemporal variation trends of rainfall erosivity. The results show that the average annual rainfall erosivity in the Nandu River Basin from 1971 to 2020 ranged from 11 841.33 to 23 692.14 MJ·mm·hm^-2·h^-1, with an average value of 16 497.67 MJ·mm·hm^-2·h^-1, and the interannual variations reflect four stages, with an overall trend of rising fluctuations. The results indicate that the potential risk of soil erosion increased gradually over the study period. The annual rainfall erosivity has a change cycle of 30 years, and no obvious abrupt change occurred during the study period. Affected by the monsoon climate, latitude, elevation, spatiotemporal distribution of rainfall erosivity and erosive rainfall distribution, the rainfall erosion force was mainly concentrated in the period from July to September, accounting for 51.26% of the annual rainfall erosivity. Therefore, it is necessary to strengthen the prevention and control of soil erosion in this period, especially when rainfall erosivity peaks in August. Rainfall erosivity showed upward trends in summer, autumn and winter, but in spring, rainfall erosivity showed a downward trend. The spatial distribution of the annual rainfall erosivity decreased gradually from south to north. The variation coefficients of the meteorological stations ranged from 0.24 to 0.43, showing high regional variability. The variation coefficient of the northern region was relatively large, while that of the southern region was relatively small, and the overall trend gradually decreased from north to south. Rainfall erosivity in the Nandu River Basin was significantly and positively correlated with the erosive rainfall and elevation; and the erosive rainfall effect passed the significance test at 0.01, while the elevation effect passed the significance test at 0.05. Certain correlations were found between rainfall erosivity and both latitude and longitude, with correlation coefficients of 0.76 and 0.42, respectively, both passing the 0.01 significance test. This study can provide a reference for the prediction and control of soil and water losses and the envirommental protection in the Nandu River Basin and related typical erosion areas.

Key words: rainfall erosivity, daily rainfall model, spatial-temporal variation, soil and water loss, erosive rainfall, the Nandu River Basin