An interrogation of research on the influence of rainfall on gully erosion

Gully erosion is a major soil degradation problem in many parts of the world. Assessment of this process and its contributing factors are becoming increasingly important, especially in terms of climate change. Rainfall runoff is known to initiate and exacerbate gully erosion processes. In this paper, research over the past two decades focussing on the influence of rainfall on gully erosion is explored. A common notion is that gully erosion increases with higher rainfall intensities. However, there is some debate on the role of rainfall on gully development, with some studies suggesting large influences of extreme rainfall, while others show limited impacts. Although the rainfall factor started receiving more attention in gully erosion studies in recent decades, there is still a need to determine the influence of rainfall on gully erosion at different temporal scales. Single- and multiple events over varying temporal scales, including periodicity of extreme rainfall events, ENSO periods, and aspects such as antecedent moisture, are highlighted as areas that should be expanded in research. The interplay between gullies, rainfall, and vegetation and the risk of climate change has potential to affect these events is also underscored. The use of new advancements in technologies for gully erosion research, namely the applications of outdoor rainfall simulators, unmanned aerial vehicles and photogrammetric/digital surface modelling, has become increasingly prevalent. The advent of these technologies offers considerable potential to assess the influence of rainfall events on gully development, especially in data poor countries.