[Spatial and temporal distributions of rainfall erosivity in the Yanhe River Basin].

Rainfall erosivity (R) is a measure of effects of the rainfall factor on the potential capacity for soil water erosion. The characteristic of spatial and temporal of R value is the basis for soil erosion prediction. The spatial and temporal distributions of rainfall erosivity were analyzed using daily rainfall data collected between 1980 and 2003 from 22 rainfall stations located across the Yanhe River Basin. The results showed that the seasonal distribution of R values formed a single peak, concentrated between May and September and accounted for 91.61% of the total annual R value. The changes in annual average rainfall erosivity followed a similar trend to those for the annual average rainfall and erosive rainfall. The average annual R value was 1580.58 MJ x mm x (hm2 x h x a)(-1), the maximum annual rainfall erosivity (1981) was 2417.70 MJ x mm x (hm2 x h x a)(-1) and the minimum (1999) was 585.29 MJ x mm x (hm2 x h x a)(-1). The variation coefficient of annual rainfall erosivity was the medium with a value of 0.32. The annual rainfall erosivity was the greatest at the Shaofangbian station with a value of 2190.33 MJ x mm x (hm2 x h x a)(-1), while the least erosivity was found at the Liandaowan and Yangshan station with values of 1151.37 MJ x mm (hm2 x h x a)(-1) and 1146.87 MJ x mm x (hm2 x h x a)(-1), respectively. The annual average R values had a similar trend of spatial distribution with annual average erosive rainfall. The annual changes in R values increased at the rainfall stations of north, while those were found to decrease at other stations of Yanhe River Basin. Overall, the annual rainfall erosivity tended to decrease in the Yanhe River Basin with the trend coefficient value of -0.004.