Massive Fissures Erupting in the Earth's Crust Present a Novel Geohydrological Peril for Cities

In a concerning development, a new study published in the journal Nature has identified over 2,900 large urban gullies in the Democratic Republic of Congo (DRC), some large enough to swallow houses and roads. These gullies, deep channels caused by erosion, are spreading rapidly due to a combination of factors, including rapid urbanisation, unstable soils, unregulated construction, and a lack of drainage systems.

The researchers warn that urban gullies could soon be recognised as one of the defining urban hazards of the Global South. Intensive rainfall events, a main driver of gully formation and expansion, are becoming more frequent due to climate change, further aggravating the problem in the DRC. Future projections indicate a potential 10 to 15 percent increase in rainfall intensities in tropical Africa over the coming decades.

The situation is likely to get worse over the coming decades due to urbanisation and increased rainfall. The populations of many African nations are booming and experiencing a rapid shift to urbanisation. In the DRC, the number of people living in areas threatened by expanding gullies doubled from 1.6 million to 3.2 million from 2010 to 2023.

The researchers argue that the absence of infrastructure to safely channel and store rainwater is helping gullies spread like open wounds through urban neighbourhoods. Prevention may be key in addressing the issue of urban gullies, as stabilising existing gullies is costly and complex. Simple engineering solutions, like shallow drainage channels and "swales", could make a difference in preventing urban gullies.

Another tactic is to redirect runoff away from erosion-prone slopes to prevent new gullies from forming. The team believes that the problem of urban gullies is a challenge that many countries need to start taking seriously. The study suggests that the problem of urban gullies is likely to be a problem facing many countries across the Global South, including sub-Saharan Africa and South America.

Countries in the Global South likely facing similar problems with urban artisanal mining as in the Democratic Republic of Congo include various African nations such as Somalia, Namibia, Zimbabwe, Mozambique, Liberia, and Lesotho. These countries share challenges of underdevelopment, poverty, and resource dependency that often accompany informal mining activities.

The gullies have displaced an estimated 118,600 people between 2004 and 2023, forcing families to abandon homes and communities. The continent is becoming increasingly wet and prone to freak rainstorms, which could exacerbate the problem of urban gullies. The team urges governments and international organisations to take urgent action to address this growing threat.

Massive Fissures Erupting in the Earth's Crust Present a Novel Geohydrological Peril for Cities