Determining the influence of catchment area on intensity of gully erosion using high-resolution aerial imagery: A 40-year case study from the Loess Plateau, northern China

Gully erosion can be a serious threat to ecologic and socio-economic stability. Although gully erosion intensity is highly impacted by catchment area changes, few studies have focused on the relevant mechanisms. This study presents a new approach to studying this issue by combining historic aerial photography and recent unmanned aerial vehicle (UAV) imagery to determine changes in gully morphology over 40 years on China's Loess Plateau, one of the world's most erosion-prone regions. Aerial photographs from 1976 were matched with UAV imagery taken in 2017 to compare gully and surface conditions in two study areas over time. Next, a new method was developed for calculating changes in gully volume and erosion moduli based on the UAV-derived digital surface model. Finally, the impacts of catchment area change on gully erosion moduli over the study period were analyzed. The results showed that the catchment areas decreased by 0.71-77.88%; greater decreases resulted in lower gully erosion moduli (with an exponential correlation) and reducing catchment area effectively slowed gully development. In addition, regional agricultural terrace construction has reduced the catchment areas, in turn reducing the amount of runoff entering gullies and thus reducing incision. Therefore, the management and maintenance of abandoned terraces should be strengthened by local governments and stakeholders to reduce runoff-induced gully erosion and sediment loss from upslope areas. The methodologies and results of this study have the potential to provide significant scientific references for the conservation of runoff and sediment in erosion-prone regions of China and elsewhere.