The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
In many steeply-sloping areas of the world, agricultural terraces are used to enable farming. Terraces change the shape of the slope, but also alter the distribution of the soil and they greatly modify the hydrology. I think it is generally considered that well-maintained and well-designed terraces are good for the mitigation of shallow landslides, although a failure to maintain them can have disastrous consequences. There is, however, a lack of high quality studies to understand this properly in many parts of the world.
There is a very interesting new paper (Sibomana et al. 2025) in the journal Catena that examines the role of agricultural terraces in landslide occurrence in NW Rwanda. The study examines a mountainous area in which extensive terracing has recently been introduced. This area has been the subject of three large rainfall events; the research examines the occurrence of landslides in terraced areas, and compares this with that of areas that have not been terraced.
The Google Earth image below, from August 2020, shows a part of the study area (centred here on [-1.75804, 29.516922]). This image was collected after an intense rainfall event in 2020:-
The image shows a landscape that has been extensively, but not exclusively, terraced, but also multiple shallow landslides, some of which are quite large and destructive.
The terraces in this area are surprisinglyrecent, with many of the terraces having been constructed since 2010. Unfortunately, the area has been impacted by three disastrous rainstorms – in 2016, 2018 and 2020, which have betweeen them have led to 70 fatalities. The three rainstorms affected different areas of the study region.
Sibomana et al. (2025) have constructed inventories for the landslides triggered by these three rainstorms – 4,687 failures in total. These are mostly shallow landslides consisting of soil and debris. Intriguingly, landslide occurrence on areas with terraces was about three times that of unterraced land. However, there are other differences in the populations. Most notably, landslides on terraces tend to be slightly smaller.
This result has important implications for the management of the landscape of this area of Rwanda. This is a critically important agricultural area for Rwanda, and terraces are an essential part of the development of farming. The study asks whether the style of terraces that are being constructed is appropriate – perhaps a change in the design could reduce the occurrence of failure? In addition, it perhaps suggests that changes are needed to the way in which water is being managed on the terraces, in particular during heavy rainfall. Many mountainous areas with terraces have evolved over decades or even centuries, and thus the approach has been honed through hard-won experience, whereas the terraces in Rwanda are comparatively modern. Perhaps there are still lessons still to be learnt?
This area will undoubtedly suffer significant rainstorms in the future, so further work is needed to understand how best to manage these key agricultural areas. As moving away from terracing is not an option, trying to reduce the failure rate is essential.
Reference
Sibomana, P. et al. 2025. Effects of agricultural terraces on landslide occurrence: Insights from a tropical mountainous region (Rwanda, Africa). Catena, 253, 108898.
https://doi.org/10.1016/j.catena.2025.108898.