Purpose

A comprehensive investigation of rainstorms and its impact on soil erosion on hillslope are important, but field observed data are rare worldwide. We aimed to assess and quantify the magnitude of soil erosion and its subsequent influence on hillslope with different land use pattern under an extreme rainstorm.

Methods

We studied an extreme rainstorm on July 26, 2017 in Zizhou county on the Loess Plateau, China. 218 mm rain fell within 15 h with a maximum intensity of 52 mm h⁻¹ for 1 h. In rainstorm core, we investigated soil erosion characteristics on six hillslopes with different land use patterns which composed of sloping farmland (SF), grassland (GL), woodland (WL) and pasture (PA) on different slope positions. Three soil erosion types (rill, slope failure and gully incision) along the six hillslopes were measured in each land, respectively. The stream power was calculated to quantify the erosion effectiveness of rainstorm. The subsequent alteration of serious gully and slope failure were measured after two years.

Results

The soil erosion intensities of hillslopes were in range of 6.94 × 10³-95.89 × 10³ t km⁻². Soil erosion intensities on hillslopes with sloping farmland were several decuples larger than that on the hillslopes with woodland and grassland. Gully incision and slope failure supplied the most sediment of hillslope while rill erosion cannot be ignored only in sloping farmland. The scarce vegetation cover, the concave surface, side slope with large height, unreasonable drainage ditch and weeding were the main reasons for the serious erosion under this storm event. The gully incision thresholds of stream power were about 175 W m⁻², 370 W m⁻², less than 35 W m⁻² and more than 460 W m⁻² for PA, GL, SF and WL, respectively. Almost all the sediment of gully transported from hillslope into downslope channel. The risk of gully incision increase 5 fold and decrease to 14 % in fallow farmland and farmland under cultivation after rainstorm.

Conclusions

Woodland and grassland with high vegetation coverage stood the erosion test of this extreme rainstorm due to high anti-erosion ability instead of runoff reduction and sediment interception. Reasonable agricultural management, such as avoiding weeding before extreme rainstorm and filling gully after erosion reduced decuples of erosion risk. Natural recovery of slope surface is not expected in these fragmentized slopes during a short period.