Urban areas at greater risk for landslides due to the effects of precipitation

A new study indicates that urbanized areas are more prone to landslides caused by precipitation than rural areas.

Annually, landslides are one of the most severe natural disasters that causes numerous fatalities and financial damage of millions. Generally, the majority of landslides are triggered by precipitation, although plenty of other factors can contribute simultaneously to slope destabilization, especially in urban areas. Due to the fact that urbanization is increasing rapidly and the amount of precipitation is expected to intensify even more in the future, it is important to take into account the influence that precipitation has on urban landslides, also as a consequence of climate change. 

The study took into consideration and analyzed data from the NASA Cooperative Open Online Landslide Repository, a big database of landslides across the Pacific coast of the U.S. This region was considered suitable because of its orography and weather variations. Using panel regression with fixed effects, the influence of precipitation characteristics and changes was differentiated.  The researchers tested factors, such as slope steepness and wildfires, to result in the fact that for the same increase of precipitation in urban and rural areas, the urban ones have 10 times higher probability to be affected by a landslide, showing the profound connection between precipitation and landslides in cities.

Although the majority of the landslides due to precipitation took place in non-urbanized areas (65%), the number of landslides relative to the area they occurred was significantly higher in urban areas. This big difference between the two areas seems to have resulted from the human alterations to the urban areas, intervening to the normal impact of precipitation on slopes stability. The conditions under which urban landslides occur, are influenced by the intrusive changes in the topography of the cities area and mainly by the lack of vegetation. Precipitation usually causes landslides by weakening the slopes and washing away surface materials, which in combination with human technical works, such as road constructions and retaining walls, as well as due to climate change, future increase of rainfall, can lead to unforeseen results, catastrophic for densely populated areas.

The authors of this study point out, for the first time, the strong connection of precipitation-triggered landslides and urbanization, by quantifying the difference between urban and rural landslides. Through this research, the prediction of landslide hazards can be enhanced in cities, depending on the specific land use of each region, expanding the use of the models developed. In addition, by quantifying the amount of precipitation in each region and by the general correlation between the two parameters, it may be easier to understand when a landslide is about to occur. As a result, the observation of this phenomenon could be useful in improving hazard assessments and indicates the importance of the interactions between urbanization and natural disasters and how people can adapt to them and be more aware.