Climatological Perspectives on the Rainfall Characteristics Associated with Landslides in Western North Carolina

Abstract

Landslides are a significant hazard in the mountains of North Carolina. While previous studies have estimated the critical instantaneous rainfall rates that may trigger a landslide, very little is known about the climatology of rainfall events associated with landslides. The rainfall climatology of a sample of landslide events in western North Carolina from 1950 to 2004 is presented in two parts. First, the two-day concurrent and cumulative antecedent (from 4 to 90 days prior to slope movement) rainfall totals are assessed climatologically by ranking them relative to all heavy precipitation events observed in western North Carolina over a 55-year period. Second, the storm types responsible for the rainfall associated with each landslide event are determined using a manual weather map classification scheme. Forty-seven percent (47%) of the landslide events are connected with concurrent rainfall totals that exceed a one-year return period. In almost half of these cases, the heavy rainfall is associated with a tropical cyclone passing through the region. The other major storm types connected with landslide events (i.e., synoptic and cyclonic-type events) generally display lower rainfall intensities and longer durations compared to tropical cyclones. Landslide activity shows the strongest relationship with antecedent precipitation totals over a 90-day period, which is the longest time period examined in the study. In many cases, a tropical cyclone produced heavy rainfall over the landslide location between 30 and 90 days before the event.