Urban Expansion on Mountain Slopes Increases Risk from Slow-Moving Landslides

As cities expand into mountains, the threat from slow-moving landslides—often overlooked in risk assessments—could endanger hundreds of thousands of people worldwide. A groundbreaking study published in Earth’s Future has uncovered a growing risk associated with slow-moving landslides, particularly in urbanizing mountainous regions.

Slow-moving landslides, which can advance at a rate as low as one millimetre per year to several meters annually, often go unnoticed. Despite their seemingly gradual movement, these slides can cause significant damage to infrastructure and may accelerate suddenly, especially in response to heavy rainfall. This sudden acceleration can lead to severe consequences, including fatalities in rare cases.

KEY FINDINGS

The study, led by Joaquin Vicente Ferrer from the University of Potsdam, is the first global assessment of slow-moving landslides and their impact on urban populations. The research involved mapping 7,764 large slow-moving landslides across regions deemed high-risk by the Intergovernmental Panel on Climate Change (IPCC).

The findings reveal that 563 of these landslides are located in inhabited areas, affecting hundreds of thousands of residents. The highest densities of settlements on slow-moving landslides were observed in north-western South America and south-eastern Africa, with significant populations also in Central Asia, northeast Africa, and the Tibetan Plateau.

The study underscores that as urban centres expand, they often encroach upon these hazardous slopes. In poorer regions, where alternatives are limited, new developments are frequently built on unstable ground, exacerbating the risk.

CLIMATE IMPACT AND URBANIZATION

The research also examines the link between climatic conditions and slow-moving landslides. Intense precipitation and shifts from dry to wet conditions are known to trigger and accelerate these slides. Increased flooding, which forces people to relocate to higher ground, often results in more settlements on unstable slopes.

Regions experiencing heightened flooding, such as western North America and southeast Africa, were found to have a stronger association with settlements on slow-moving landslides. The study calls for improved landslide mapping and monitoring, particularly in poorly documented areas like the Hindu-Kush Himalayas and the East African Rift.

RECOMMENDATIONS AND FUTURE RESEARCH

The study highlights the need for enhanced landslide detection and monitoring efforts, especially in regions with limited data. Ferrer emphasizes the importance of ramping up mapping and monitoring in high-risk areas to better understand and mitigate the risks posed by slow-moving landslides.

“Our research provides a comprehensive global assessment of slow-moving landslides, offering valuable insights into their impact on urban populations and the need for improved monitoring,” Ferrer said.

Despite limitations in landslide inventories, the study’s findings are crucial for addressing the risks associated with urban expansion on unstable slopes and ensuring safer development practices in mountainous regions.