Water erosion response to rainfall and land use in different drought-level years in a loess hilly area of China

Due to rainfall variation and poor land cover, water erosion in the loess hilly area is severe and experiences high temporal fluctuations, which increase the difficulties of erosion quantification, prediction and control. In this study, 15 runoff plots were implemented in Dingxi, a typical loess hilly area of Gansu Province since 1986. Three typical years representing WY (wet year), NY (normal year) and DY (drought year) were firstly filtered based on the consecutive rainfall-erosion data and an aridity index. Then, water erosion dynamics involving five land uses (cropland, alfalfa, scrubland, woodland and grassland) in the three typical years were analyzed. The following results were found. Firstly, the most severe annual erosion rates did not appear in WY, but in DY. Moreover, the rates in DY were far higher than those in NY and WY. Secondly, although total rain depth and number of events were in the order of WY > NY > DY, mean maximal intensity of erosive rainfall however, was in the order of DY > NY > WY. This finding is important for erosion control. Namely, we cannot judge water erosion degree just from annual rainfall. More attention should be paid to the specific rainfall variables and distributions. Thirdly, different land uses played an important role with sea buckthorn reducing water erosion in contrast to spring wheat cultivated on steep slopes. Lastly, regardless of different drought-level years, only a few number of events with high intensities were responsible for the majority of annual soil and water loss.