中国科学院水利部水土保持研究所机构知识库

Obtaining practical thresholds for erosive rainfall plays a crucial role in calculating rainfall
erosivity and predicting water erosion. Nevertheless, the study of thresholds on subwatershed and
watershed scales remains scarce. Given this, we presented the critical rainfall that generated the
outflows of subwatersheds and watersheds as the threshold of sediment-generating rainfall. On the
basis of the observation of twelve nested topographical units at the Peijiamaogou watershed in the
Loess Plateau of China, we fitted regression relationships between rainfall indexes (rainfall amount,
maximum 30-min intensity, maximum 60-min intensity, rainfall amount multiply maximum 30-min
intensity, and rainfall amount multiply maximum 60-min intensity) and the proportion of cumulative
sediment yield to the total sediment yield. We determined the thresholds of sediment-generating
rainfall and explored the variabilities of thresholds across di erent spatial scales. Moreover, the
covering area proportion (CAP) with rainfall indexes higher than the thresholds was also employed as
thresholds at the subwatershed and watershed scales. The thresholds of CAP for P and I30 were 50.5%
and 47.6% at the subwatershed scale, while 31.0% and 30.3% at the watershed scale. The thresholds
of P and I30 at the subwatershed scale were higher than those of hillslope scale, while the threshold
of I30 at the watershed scale was smaller compared to the other scales. In general, I30 was viewed
as the best threshold among single rainfall indexes across di erent spatial scales, while P was not
recommended as a practical threshold. This study can improve the prediction accuracy of water
erosion across di erent spatial scales and develop the spatial scale e ect of sediment yield in the loess
hilly areas.