The frequency of landslides in the Pittsburgh region is often determined by the amount of rainfall experienced.
Since landslides involve the movement of an unstable mass or rock and unconsolidated earth or debris down a slope, rain as well as other water sources can serve as a landslide trigger. These landslides can be a result of both natural occurrences and of human alteration of the land and its topography.[i]
During 2018 the Pittsburgh region experienced record rainfall. Previous to 2018 the wettest year on record for Pittsburgh was 2004, when the city experienced 57.41 inches of rain. By early October, 2018, the Pittsburgh region had received nearly 46 inches of rain, about 16 inches above the normal yearly precipitation average.[ii] This suggests that it is almost certain that 2018 will become the record year for precipitation. The region also experienced the second greatest daily precipitation on record on September 9, 2018, when it received 3.73 inches of rain.[iii]
The Pittsburgh region has long been recognized as an area of major landslide activity as we have discussed and during 2018 the region experienced a record number of landslides. The city Department of Mobility and Infrastructure has counted more than 24 slides this year that caused major street and property damage. In addition, slides have damaged more than 19 county roads and 78 slides impacted state roads in Allegheny, Beaver and Lawrence counties. Landslides have also damaged or destroyed numerous private residences, apartment and commercial buildings, and various infrastructures.[iv]
There is wide-agreement among climate scientists that climate change and warming of the climate system will almost certainly increase precipitation.[v]
The Pittsburgh region is a prime candidate for such an increase. Higher temperatures mean that the atmosphere can hold more moisture and probably result in heavier bursts of rainfall. Such heavier bursts have marked the rainfall the Pittsburgh region experienced this year, affecting the stability of natural and engineered slopes and leading to an increase in the number of landslides and floods. Most forecasters foresee a continuation of this precipitation pattern due to climate change. Pittsburgh geologic conditions and past landslide history in the context of climate change suggest that the region must take precautions to guard against damages from a reoccurrence of this year’s damaging and costly landslide experience.[vi]
[i] DCNR, Landslides in Pennsylvania, 3d printing, Harrisburg, 2006, p. 1.
[ii] National Weather Service, “NWS Pittsburgh Climate Data: Precipitation Records,” at https://www.weather.gov/media/pbz/records/prec.pdf/
[iii] NWS, “Greatest Daily Precipitation on Record,: Precipitation Records,” at https://www.weather.gov/media/pbz/records/prec.pdf/
[iv] Adam Smeltz, “Slipping downhill: Are Western Pa.’s proliferating landslides just the start, Pittsburgh Post-Gazette, Oct. 11, 2018, http://www.post-gazette.com/local/city/2018/10/10/Pittsburgh-Allegheny-County-landslides-PennDOT-budget-rainfall-records-Bill-Peduto/stories/201810080141
[vi] Stefano Luigi Gariano and Fauston Guzzelli, “Landslides in a changing climate” Earth-Science Reviews (Nov. 2016) V. 162, 227-252.