The Prolonged Influence of Urbanization on Landslide Susceptibility Estimates

Landslides pose a threat to life, property, and economic developments but are also influenced by urbanization processes that are sometimes associated with such developments. Processes such as urban expansion, and the associated land-use changes and road construction can reduce vegetation cover, displace sediments, and modify surface and subsurface hydrology. These changes can affect the susceptibility of hillslopes to landslides and thus quantifying the influence of urbanization on landslide occurrence can help design sustainable development efforts. Although landslide susceptibility has been shown to increase immediately after urbanization, the prolonged effect of urbanization on landslide susceptibility remains largely unquantified. To quantify this effect, we analyzed landslide occurrence in Southwestern Pennsylvania, where urbanization mostly occurred multiple decades ago. We used road density as a proxy for urbanization, divided the study area into regions of high and low road density, and estimated landslide susceptibility in these regions based on a landslide inventory digitized from landslide maps produced by the United Stated Geologic Survey in the 1970s and 1980s. We examined and compared the association of different anthropogenic, geologic, and topographic factors with landslide occurrence in these different regions based on both random forest and conditional probability analyses. Results are consistent between analysis methods and show that the primary factors that are associated with landslide occurrence differ between areas of different degrees of urbanization, and that the association of landslides with anthropogenic factors is stronger in urbanized areas. Overall, our findings suggest that urbanization continues to enhance the susceptibility to landslides for multiple decades.