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Urban areas more likely to have precipitation-triggered landslides, exposing growing populations to slide hazards

Urban areas may be at greater risk for precipitation-triggered landslides than rural areas, according to a new study that could help improve landslide predictions and hazard and risk assessments. Landslides cause thousands of deaths and billions of dollars of damage annually. With over half of the world’s population in urban areas, and both urbanization and…

Urban areas may be at greater risk for precipitation-triggered landslides than rural areas, according to a new study that could help improve landslide predictions and hazard and risk assessments.

Landslides cause thousands of deaths and billions of dollars of damage annually. With over half of the world’s population in urban areas, and both urbanization and precipitation extremes expected to increase in the future, understanding how urban landscapes are affected by precipitation-triggered landslides is a pressing need.

The new study used a large database of precipitation-triggered landslides across the Pacific coast of the U.S. and isolated the influence of precipitation changes using a specific type of computer model. When the researchers controlled for other factors, like slope steepness, rock type, and wildfire, they found that urban landslide hazard was up to 10 times more sensitive to variations in precipitation than in rural areas. That means that the same increase in rainfall in rural and urban areas could be 10 times more likely to cause a landslide in a city.

The new research is published in the AGU journal Geophysical Research Letters, which publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

“There’s a much stronger relationship between precipitation and landslide likelihood in urban versus rural areas,” said Elizabeth Johnston, a geomorphologist and lead author of the new study. “Precipitation impacts slope stability. We’re concerned about precipitation because it’s likely that it will intensify, and this intensification could lead to greater landslide hazard in some areas. But the extent to which it increases landslide hazard isn’t known.”

While the majority, 65%, of precipitation-triggered landslides in the database occurred in rural areas, when Johnston looked at the number of landslides relative to the area in which they occurred, urban areas had an outsized number of landslides.

Johnston was surprised by the strong divide. “I didn’t set out to study urban versus rural hazards, but the urbanization signal was the strongest in preliminary models,” she said. “I recognized something was there.”

The discrepancy is likely due to human-made changes to topography and vegetation loss in urban areas, which can weaken slopes and make them more prone to landslides. Quantitatively demonstrating higher landslide likelihood in urban areas can inform hazard mapping and help guide hazard-response funding.

Urbanization as a landslide predictor

Precipitation can cause landslides by percolating through soil and bedrock, which weakens slopes, and by washing material at the surface downhill. While other events, like earthquakes, can also cause landslides, precipitation-triggered landslides are the most

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