Effects of rainfall patterns on runoff and soil erosion in field plots

Soil erosion processes during a storm are strongly affected by intra-storm variations in rainfall characteristics. Four storm patterns, each with a different rainfall intensity variation were separated. The storm patterns were: (1) increasing rainfall intensity (2) increasing then decreasing intensity (3) decreasing intensity (4) decreasing then increasing intensity. After each erosive rainfall (12 events), Runoff and suspended sediment samples were collected in each plot׳s tank which is located on hillslopes of the basin of Khamsan. Main storm characteristics and soil losses were plotted and equation of the line of best fit were selected. Analysis of variance (ANOVA) was used to determine response of runoff and soil erosion to storm patterns. Results showed that in lower rainfall intensities a linear function fits the relationship between soil loss and rainfall intensity whereas this function tends to be non-linear at higher intensities. Also a strong non-linear relationship was found between different quartiles of storm and soil loss. Statistical analysis revealed significant differences in total runoff, soil loss and sediment concentration across four storm patterns (P<0.001) but no differences in the runoff coefficient. In particular, storms with increasing rainfall intensity yielded highest quantities of eroded sediments, total runoff and highest sediment concentrations followed by increasing then decreasing, decreasing then increasing and decreasing intensity, respectively.