where Mi is the half-month rainfall erosivity (MJ mm ha−1 h−1 yr−1) and Dj is the effective rainfall for day j in one half-month. Dj is equal to the actual rainfall if the actual rainfall is greater than the threshold value of 12 mm, which is the standard for China's erosive rainfall.
Otherwise, Dj is equal to zero (Xie et al., 2000). The term k is the number of days in the half-month. The terms α and β are the undetermined parameters: