Environment: Urbanization of tropical hillsides can increase landslide risk

A landslide underneath the large, rapidly-growing city of Bukavu, Democratic Republic of the Congo has accelerated in recent years according to a study published in Nature Geoscience.  This findings suggest this may be due to unplanned urban sprawl modifying surface and subsurface water flows.

Landslides are common throughout the tropics and represent a growing hazard to human health and infrastructure as cities expand up landslide-prone hillslopes. Deep-seated landslides, which occur tens of metres below the surface can gradually modify large areas over many years. The behaviour of deep-seated landslides is closely tied to the pressure of water within hillslope soils, though it has been unclear whether urbanization impacts the hydrological balance and increases landslide risks.

Antoine Dille and colleagues analysed satellite radar data from 2015 to 2019, alongside 70 years of aerial photos, to explore the role of urbanization on changes in the motion of a deep-seated landslide beneath Bukavu, Democratic Republic of the Congo. They found that some sections of the landslide are moving up to three times quicker than in the 1970s, and suggest this is not as a result of precipitation changes or earthquakes. They show that the fastest sections — currently moving on average 0.7 metres each year — are those that urbanized most rapidly. Instead, destabilization of the landslide is most acute in areas where the re-routing of surface runoff and leaky underground infrastructure have combined to increase soil water saturation.

The authors conclude that effective, community-based management of groundwater infiltration, and understanding of how anthropogenic activity influences surface processes, is critical to mitigating landslide risks in Bukavu and many other growing cities in the tropics.