In the sprawling urban landscapes of the Democratic Republic of the Congo (DRC), a silent yet formidable geological evolution is reshaping neighborhoods and threatening livelihoods. Recent research led by a team of Congolese and Belgian scientists has meticulously documented the rise and intensification of urban gullies across 26 cities in the country, revealing a dramatic environmental and humanitarian crisis that has largely escaped public attention despite its profound consequences.
Gullies, defined as large and deep incisions eroded into the terrain by concentrated surface runoff during heavy rainfall, represent a geomorphological phenomenon of considerable scale and impact. These erosional features develop where water flow exceeds the soil’s capacity to resist, carving out channels that can span hundreds of meters in length and several meters in width. Unlike minor erosion forms, gullies disrupt urban infrastructure by bisecting roads, neighborhoods, and essential services, thus fracturing the fabric of daily life and urban mobility.
The formation of gullies is a natural hydrogeological process intensified under specific landscape and climatic conditions, but in the DRC’s urban context, human activity plays a predominant role. Unplanned expansion of cities onto vulnerable terrains, especially steep slopes, combined with inadequate drainage systems and poorly maintained roads, magnifies water concentration and soil destabilization. These anthropogenic factors amplify the frequency and magnitude of gully formation, transforming a natural hazard into an escalating urban disaster.
Leveraging advances in spatial technology, the research team utilized ultra-high resolution satellite imagery with ground resolutions at or below one meter, enabling the precise identification and mapping of individual gullies across vast urban expanses. This was complemented by extensive field validation encompassing over 400 sites to verify the remote sensing data and to understand the local geomorphic contexts. The integration of demographic data allowed for a comprehensive assessment of human exposure and displacement associated with these erosional features.
Between 2004 and 2023, the study identified nearly three thousand urban gullies, resulting in the displacement of over 118,000 residents, a figure that alarmingly escalated after 2020. Historical aerial photographs from the mid-20th century juxtaposed with recent data illustrate that before the country’s accelerated urbanization, only isolated gullies existed, predominantly in less developed road corridors. The spatial correlation with modern road networks implicates infrastructure development without sufficient erosion control as a significant driver in gully genesis.
The environmental and social repercussions of urban gullies extend beyond immediate displacement. These incisions accelerate sediment transport, degrade soil quality, and interrupt water catchment functions, undermining urban resilience to climate variability. Gully expansion can render areas uninhabitable, provoke secondary hazards such as landslides, and impose enormous economic burdens on communities and municipalities struggling with repair and mitigation.
Despite the severity of these impacts, urban gullies have received limited attention compared to other geohazards like earthquakes or floods. This lack of recognition is partly due to their gradual progression and localized visibility, earning them the description of “silent disasters.” However, given their rapid proliferation in rapidly urbanizing African cities, there is an urgent need for a paradigm shift in urban risk management strategies to incorporate erosion hazards.
The research posits prevention as the most effective approach to counter the scourge of urban gullies. Engineering solutions currently employed to stabilize established gullies involve exorbitant costs, often exceeding one million US dollars per site, which is financially unsustainable for many local governments. Alternatively, integrating erosion risk into early urban planning and road construction standards promises a cost-efficient pathway to safeguard communities by mitigating gully formation before it reaches critical stages.
Implementing effective prevention requires recalibrating urban design principles to account for the intricate interplay of topography, hydrology, and anthropogenic pressures. This includes reimagining drainage infrastructure to enhance water retention and dispersion, enforcing land-use policies that avoid construction on susceptible slopes, and adopting erosion-resistant road designs. By doing so, cities can significantly reduce runoff concentration and soil exposure, arresting the initial stages of gully development.
Furthermore, the development of predictive geospatial models based on historical and real-time data can empower planners and emergency responders to identify high-risk zones proactively. Such models leverage variables including rainfall patterns, soil types, land cover, and urban expansion rates to forecast areas susceptible to gully initiation. Early intervention strategies—ranging from bioengineering to targeted infrastructure maintenance—can then be deployed, halting erosion processes before they inflict severe damage.
Importantly, the methodology pioneered through this research in the DRC is inherently transferable. It offers a replicable framework for mapping and monitoring urban gullies in other rapidly expanding cities of the Global South, many of which face similar socio-environmental challenges. By harnessing satellite imagery, demographic analytics, and field surveys, cities can establish erosion inventories that inform sustainable development and disaster risk reduction policies.
As urbanization continues unabated across sub-Saharan Africa, the phenomenon of urban gullies is poised to become a widespread geohydrological hazard with potentially catastrophic effects. The study encapsulates a critical message for policymakers, urban planners, and scientists alike: acknowledging the scale of erosion threats, integrating them into regulatory frameworks, and prioritizing preventative measures are essential steps to avoid transforming city streets into destructive canyons.
In sum, these findings underscore the intricate nexus between human-induced landscape changes and natural geomorphological processes, revealing a complex hazard that reflects broader challenges of sustainable urban growth. Mitigating the threat posed by urban gullies demands a multidisciplinary, forward-looking approach grounded in innovative mapping technologies, informed urban planning, and community engagement—transforming silent disasters into manageable urban risks.
Subject of Research: Quantification and impact assessment of urban gully erosion in the Democratic Republic of the Congo
Article Title: Mapping urban gullies in the Democratic Republic of the Congo
News Publication Date: 27-Aug-2025
Web References: http://dx.doi.org/10.1038/s41586-025-09371-7
Image Credits: Mathias Vanmaercke / KU Leuven
Keywords: urban gullies, erosion, geomorphology, hydrogeology, Democratic Republic of the Congo, satellite imagery, urban planning, displacement, risk management, sustainable development, geospatial analysis, urbanization
