Temporal Trend in Landslide Occurrences in Post-fire Areas over the Past Two Decades

Abstract

Analyzing the effects of forest fires on sediment dynamics is essential to establish effective mitigation measures to reduce the risk of fire-related sediment disasters, such as landslides, debris flows, and hyperconcentrated flows. The objective of this study was to investigate the temporal trend in landslide occurrences after a forest fire based on the statistical data of forest fires and landslides recorded over the past two decades. The results suggested that the landslide occurrences in the post-fire area increased the most in 1 - 5 years after the fire. Typically, landslide occurrences in the post-fire area decreased as the burnt slopes were covered with grass and shrubs within five years after a fire. However, our data showed that the frequency of landslide occurrences revealed relatively higher value until 6 - 10 years after the fire. This result was considered owing to the decrease in relative resistance to landslides initiated by root decay in the burnt slopes. Overall, the risk of landslides after forest fires is presumed to be higher than the pre-fire condition for the period that the root system of burnt slopes is regrowth and recovery (10 - 20 years or more after the fire).