A Comparative Analysis of Runoff and Soil Loss Characteristics between "Extreme Precipitation Year" and "Normal Precipitation Year" at the Plot Scale: A Case Study in the Loess Plateau in China

The highest annual precipitation in Ansai during the past 60 years was observed in 2013. Studying the effects of such extreme annual precipitation on soil erosion can deepen similar research and help predict environmental damage under future extreme rainfall. We selected the runoff plots (area: 4 m x 10 m) of three land-use types: cultivated land (C), wild grassland (W) and switchgrass (S). We monitored corresponding indices in the extreme year (2013) and normal year (2010-2012). The results were as follows: (1) The rainfall parameters (rainfall amount, EI30, EI60) in the extreme year were all higher than those in the normal year, especially in July; (2) In July and August, the runoff and soil loss of cultivated land in the extreme year increased by 1492.5% and 538.2%, respectively, compared to those in the normal year. The silt content of sediment was the highest generally, but the sand content increased relatively in the extreme year; (3) The effect of rainfall on soil erosion was the smallest in W; (4) In the extreme year, the same EI30 generated more runoff and soil loss than those in the normal year. The high antecedent precipitation which would cause high antecedent soil moisture was one of the reasons. The threshold value (100 MJmmha(-1)h(-1)) of EI30 related to extreme erosion risk was proposed.